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13g1 ELECTRONICS

PROJECTS

from ELECTRONICS,

A FAWCETT BOOK

LARRY EISINGER

GEORGE TILTON

SILVIO LEMBO

HAROLD E. PRICE

NUMBER 649

EDITOR -IN -CHIEF

MANAGING EDITORART EDITOR

ASSOC. ART EDITOR

W. H. Fawcett, Jr. President

Roger Fawcett General ManagerGordon Fawcett Secretary -Treasurer

Roscoe K. Fawcett Circulation DirectorDonald P. Hanson . . . Assistant General ManagerGeorge H. Allen Vice PresidentRalph Daigh ' Vice PresidentR. Bruce Besten Production DirectorAl Allard, Ralph Mattison Art Directors

JOSEPH PIAZZA EDITOR

Mike GaynorAlex SantiagoMel Skriloff

STAFF ARTISTS

Bill Kuch

John SelvaggioHerbert JonasPaul Howard

Catherine S. Carr Production EditorClaire Herman Assistant Production Editor

BEST ELECTRONICS PROJECTS FROM ELECTRONICS ILLUS-TRATED, Fawcett Book 649, is published by Fawcett Publica-tions, Inc., Greenwich, Connecticut. Editorial and AdvertisingOffices: 67 West 44th Street, New York, New York 10036.General Offices: Fawcett Building, Greenwich, Connecticut06830. Printed in U.S.A. Copyright © 1966, 1967 by FawcettPublications, Inc. BEST ELECTRONICS PROJECTS FROM ELEC-TRONICS ILLUSTRATED is registered in the U.S. Patent Office.

Printed by Fawcett -Haynes Printing Corp., Louisville, Ky.

Fawcett Publications, Inc., is a member ofAmerican Book Publishers Council, Inc.

CONTENTSTonics for Tape Recorders 4Flip Flop 10In -a -Socket Dimmer 13How Do You Do It? 16Those Multiplying Cells 19

Add a Monitor Head toYour Recorder 22

Super -Speed Strobe 24FM Guitar Broadcaster 30The Easy Way to Install

CB in Your Car 34Crystal -Controlled

SW Signal Generator 37A Sizable Speaker System 41

The Secret of theNew Electric Cars 43

2 Meters on 2 Tubes 47Automatic Telephone

Answering Service 51

Vest -Pocket Modulation Scope 627 Steps to Better Tapes 67Char -Analyst for Batteries 71

Band -Switched VHFer 75CB Alignment Generator 79Try an Attic Antenna 84Gate -Dip Oscillator 87Probe -Size Signal Injector 91

Stamp Out Mobile Noise 94All Purpose Audio Mixer 97CB Control Console 102Pocket CB Converter 107The Case of the Buried Treasure 110

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The "Edu-Kit" offers you an outstanding PRACTICAL HOME RADIO COURSE at arock -bottom price. Our Kit is designed to train Medic A Electronics Technicians, makingse of the most modern methods of home training. You will learn radio theory. construe -ion practice and mrvicing. THIS IS A COMPLETE PADIO COURSE IN EVERY DETAIL.

You will learn how to build radios, using regular schematics; how to wire and soldera professional manner; how to service radios. You will work with the standard type of

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You will receive training for the Novice, Technician and General CI of F.C.C. RadioAmateur Licenses. You will build Receiver, Transmitter, Square Wave Generator, CodeOscillator, Signal Tracer and Signal Injector circuits, and learn how to operate them. Youwill receive an excellent background for television, Hi-Fi and Electronics.

Absolutely no previous knowledge of radio or science is required. The Edu-Kit" is theproduct of many years of teaching and engineering enperience. The "Edu-Kit.. will provide.you with a basic education in Electronics and Radio, worth many times the low priceyou pay. The Signal Tracer alone is worth more than the price of the Kit.

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PROGRESSIVE TEACHING METHODThe Progressive Radio "Edu-Kit" is the foremost education

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You begin by examining the various radio parts of the "Edufunction, theory and wiring of these parts. Then you nuild a siset you will enjoy listening to regular broadcast stations, leaand trouole.shooting. Then you build a more advanced radio, I

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3

By SURE, it may haveHERMAN BURSTEIN seen better days andplayed sweeter music. And it probably couldboast that enough tape has passed its headsto reach the moon. It has aged quite a bitsince it was unpacked but, like most old taperecorders, it just won't lie down and die. It'spooped -out, all right, but a shot or two in thearm will give it new life.

Heads go askew, dirt accumulates in thewrong places, the drive mechanism faltersand tubes give up the ghost. It's an easymatter to rescue a recorder long beforesounds get soggy. All it takes are sharp ears,a few accessories, plus a VTVM and anaudio generator.

PreliminariesEven if your machine still produces good

sound, a bit of routine maintenance will helpkeep it that way. Most important thing is tokeep the heads clean. Swab away bits of dirtand tape oxide with a Q -tip moistened in tape -head cleaner. Remove deposits from theerase, record and playback heads as well astape guides, rollers and posts. And all thosemetal parts that contact the tape also shouldbe demagnetized at this time. If your machineuses drive belts, replace them if there aresigns of stretching. Replace all rubber that's

worn flat or is made rock hard by ageing.Gently move the connecting cables be-

tween input and output connectors and themachine's electronics while making a testrecording. Do the same with leads to theerase, record and playback heads. If humlevel changes or there's noise, look for abroken or loose connection. Lubricate the ma-chine exactly as explained in the manufac-turer's instructions. Don't squeeze the oilcan too hard, and wipe away all excess oil-especially if it's near the rubber parts. Checkall tubes on a tube tester.

Playback ResponseThose preliminaries will take care of small

but nagging things that cause general deg-radation of performance. If you want tocheck the results of your efforts, run a fre-quency -response test. The setup to use isshown in Fig. 1. A test tape (such as AmpexNo. 31321-04) is required to provide a seriesof constant -level signals from 50 to 15,000cps. If the machine has good playback re-sponse it will reproduce each tone equallywell, as indicated on the VTVM.

The procedure is to use the tape's 1,000 -cps frequency to first establish a referencelevel on the VTVM. The machine is doingfine if the meter indicates that frequencies

4

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This is one of America's fastest growing indus-tries! It offers higher pay, more job security andmore job opportunities than most other f, elds. Ifyou are 18 or over and want an exciting, big pay

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from 50 to 15,000 cps are reproduced within2 or 3 db of the reference -tone's level. (That'sfor a tape speed of 71/2 ips. At 33/4 ips, don'texpect the same high -end response.)

Test tapes cost plenty-as high as about$20 for the Ampex we specified. One way toget around this expense is to check responseby ear. It's a cinch if you taped a new recordwhen the recorder was unpacked and in mintcondition. Play that tape now and compareit with the sound from the disc. The testisn't an end all, but it can offer valuable in-formation about playback quality.

A similar test requires a few dollars forsuperior -quality prerecorded tape and a discrecording of the same musical selection.When new tape and disc are played backsimultaneously on comparable -quality equip-ment you should be able to make a reasonablygood comparison.

Most common fault during playback is lossof high -frequency, or treble, response. Thiscould arise from a worn playback head,which, of course, can be replaced. But if acomponent in the machine's electronics(other than a tube) is defective, the repairmight require the skill of a service technician.Another treble killer is poor head alignment,which we'll get to in a moment.

Record/Playback ResponseIf the recorder passes playback tests, there's

still no guarantee it will make it on a recordtest. An ear test is helpful. Copy a brandnew record on tape, then compare discagainst tape at playback.

You can make a more critical appraisal ifyou have an audio generator and VTVM.The test setup is shown in Fig. 2. Begin byrecording frequencies from 50 to 15,000 cps.Make sure the output from the generator iskept constant (using the switch, connect theVTVM to the recorder's input) and well

Fig. 2-Setup for measuringrecord/playback response ofa machine. You record audiosignals from 50 to 15,000 cps,then measure the playbacklevel with the VTVM. Purposeof the switch is to connectthe VTVM to the recorder's in-put when making the tape.This enables you to keep thelevel of input signal constant.

OUTPUT

AUDIOGENERATOR

Fig. 1-For playback frequency -response test.measure the machine's output with a test tapethat has constant -level tones from 50.15,000 cps.

below the recorder's overload point. Playback the recorded frequencies. The VTVMwill indicate how well the recorder performsduring record.

If an audio generator isn't available, nextchoice is a test record with series of tonesthat you copy on the tape. This test, of course,assumes your hi-fi equipment has substan-tially flat response. These frequency testsprovide a valuable profile of how wide andsmooth the machine's response is.

Head AlignmentHigh frequencies will disappear if the tape

doesn't move past the heads at a 90° angle,as shown in Fig. 3. If a head's position shiftsit must be corrected. If your machine hasonly one head for both record and playback-and you never intend to play a tape re-corded on another machine-head alignmentis less critical. The error cancels itself. But ahead that has moved slightly could adverselyaffect the quality of your older tapes. Bestpractice, therefore, is to adjust to 90°.

A test tape on which is recorded a steadyhigh -frequency signal is the best thing to usefor azimuth alignment of a head. Again, theindicator is a VTVM connected to measurethe recorder's output. As you play back thetape, tilt the head very slightly to the left and

OUTPUT

VTVM READSGENERATOR OUTPUT

DURING RECORDING TOINSURE UNIFORM INPUT SIGNAL.READS TAPE RECORDER OUTPUTDURING PLAYBACK TO MEASURE

OVERALL RECORD/PLAY RESPONSE

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Age

Address CountyCity &State Zip No.

Occupation Working Hours.... A.M.. ..

7

right, using the adjustment screws near thebase of the head, until the meter indicatesmaximum output.

If you don't have a VTVM, your ears willdo, too. If the frequency of test tone is toohigh for you to hear, cut the tape speed inhalf. This will make a 15,000 cps tone dropto 7,500 cps. If neither meter nor test tapeis available, you can take a crack at headadjustment while playing a prerecorded tape.Simply listen for best treble response. Thetechnique may appear sloppy, but some audioengineers prefer the ear -only, rather thanthe instrument, approach to aligning a head.

If your machine has separate record andplayback heads, first align the playback head.Then align the record head with reference toit. You do this by recording a high frequencysignal and simultaneously playing it back(usually possible on three -head machinesthat have provision for monitoring whilerecording).

Using the VTVM to monitor the playbacksignal, adjust the record head for maximumindication on the meter. If you cannot getan audio generator, try one of the other meth-ods mentioned earlier: that is, a test record'or judging by ear using music as a programsource.

Bias CurrentThis adjustment isn't for Sunday putterers,

but we'll include it anyway for serious audio-philes. (If your machine does not have a bias-

adjust control, skip over this section.)Bias is a high -frequency signal (usually

between 50 and 100 kc) which is applied tothe record head simultaneously with thesignal being recorded. It improves the signal-to-noise ratio and reduces distortion. Butyou can have too much or too little of a goodthing. Ideal bias for one brand of tape mightcause treble loss in another. If you want toattempt this adjustment, here's the generalprocedure: Find out what the manufacturerof the recorder recommends for the bias testfrequency (usually between 1,000 and 3,000cps). Then record that signal. Play backthe tape and note the playback level.

Record the tone several times each at dif-ferent bias settings. The setting that pro-duces the highest playback level is the correctone. But remember, this setting is for theparticular tape you used. Switch to a differ-ent brand and you should set the bias againfor optimum performance.

Fig. 3-Azimuth angle (angle between tape edgeand gaps in head) always must be 90°. Head'smounting screws are often used for alignment.

A second method of adjusting bias isshown in Fig. 4. You determine bias currentby measuring the voltage drop developedacross a 100 -ohm resistor inserted in one leadof the record head. Using Ohm's Law(I =E/ R) divide the voltage indicated on themeter by 100 and you get bias current. Com-pare this current with the manufacturer'srecommended current and make the neces-sary adjustment to the recorder. If you at-tempt bias adjustment without test equip-ment, you'll have to try for flattest record/playback response. Tape speed should be71/2 ips.

Head HeightThis adjustment is especially critical in

stereo machines, and you can see why in Fig.5. If the head is too highintended for a particular track may pick upsignal from another track as well. The tapeedge should be .001 in. above the upper gap.Head adjustments are much simpler with aspecial alignment tape that tells your ear, notyour eye, when head height is correct. Thetape to use is an RCA No. 12-5-64T. It hasa steady tone recorded across its entire widthexcept for track 3, as shown in Fig. 6. As thetape goes through the machine, you adjustthe playback head's position until you hearthe least signal from track 3.

Another way to make the adjustment is toplay a steady low -frequency tone recorded ona quarter -track tape and visually position the

BIAS

CURRENT

100 OHMRESISTOR

GROUND,s-LEAD

7-- GROUND

VTVM

Fig. 4-Measure voltage drop across resistor con-nected in series with record head's ground lead.then use Ohm's Law (I=E/R) to find bias current.

8

head so it's too high. Then gradually movethe head down until you hear, or note on themeter, maximum output signal. There's anadditional step if your machine has a sepa-rate record head. After aligning the playbackhead, as already described, record a low -frequency tone and simultaneously play itback. Adjust the record head for maximumplayback signal.

Some accessories make recorder trackvisible. There's Magne-See solution and aspecial viewer made by the Minnesota Min-ing and Mfg. Co. (3M). They permit youvisually to adjust record -head height, thenuse the tape as a reference for adjusting theplayback head. These accessories are alsovaluable for determining if the erase headcompletely wipes off the recorded track.Once you've made height adjustments to anyof the heads, chances are that azimuth align-ment will be disturbed slightly. Azimuthshould be rechecked and adjusted if there'sbeen any change.

Tape -Motion ProblemsIf a machine is up to professional stand-

ards, its speed is accurate to within 0.3 percent. This means that in a half hour of play-ing time the tape will run not more than 5.4seconds fast or slow. The best home machinesmay be accurate within 0.5 per cent. Somemodels are within 1 per cent. Fair machinesrun within 2 per cent.

How much your machine deviates fromthe correct speed can be determined with aspecial stroboscope tape or strobe disc (madeby Robins Industries and others). You il-luminate the tape or disc with a lamp oper-ated on 60 -cps house current. If the barson the tape appear to move in the directionof tape travel, tape speed is fast. If the barsmove in the opposite direction, the tape speedis slow. You can tell whether the error isacceptable by observing the number of barsthat move past a point (such as a pencil tip)each minute. Seventy two bars per minutemean a speed error of 1 per cent. Othererrors are proportional. For example, 36bars mean a speed error of 0.5 per cent. Butas long as you're not going to play prere-corded tapes or tapes made on other ma-chines, speed differences aren't too important.Anyway, there's not much you can do aboutincorrect speed.

Other tape motion problems are wow andflutter. You'll have to use your ear to detect

HEAD GAPS HEAD GAPS HEAD GAPSCORRECTLY POSITIONED TOO HIGH TOO LOW

11111:111111110111111MITEM

TRACK 4

TAPE

Fig. 5-Diagram shows relationship of gaps andtracks. U height of the head is incorrect. gap willpick up signal from two tracks instead of one.

them since suitable instruments are extremelyexpensive. One technique is to record andplay back a steady tone of approximately3,000 cps. (The ear is especially sensitive tospeed changes in this region.) Wow, a slow -rate change, is a wavering or souring of thetone. Flutter is a rapid change in frequencywhich imparts a grainy, indistinct quality tothe sound.

These errors in tape motion are usuallyproduced in the tape -transport mechanism.They could be due to slippage, worn or hard-ened rubber parts, mechanical wear, possiblyexcessive force pressure pads againsttape heads. But before you get inside themachine, carefully clean all parts that comein contact with the tape. Even small quanti-ties of dirt can introduce friction and drag.

Final NotesDon't overlook items outside the machine.

Get rid of bent reels that squeak whet) theyturn. They could be ruining the edges of goodtape. Lubricate your old, squeaky tapes witha silicone compound. And a final autumntonic: treat yourself to a new, inexpensive,gadget-like a tape threader to help tran-quilize fumbling fingers. $

Fig. 6-Test tape will aid you in adjusting headheight. You move the head slightly up or down un-til the output from the blank track (3) is at minimum.

l)

FLOP FLIP FLOP FLIP FLOP FLIP

TAKE two transistors, add a half dozenor so standard parts and you have what's

called a flip-flop-the building block of com-puters. On a more down-to-earth level, flip-flops are used to lock your TV picture in withthe signal from the transmitter. To see howone works, we're going to build a flip-flopaudio generator and light flasher.

The first flip-flop we'll talk about is calledan astable (not stable-it operates contin-uously after power is applied) or free -run-ning multivibrator. Basically it is an elec-tronic see -saw in which two transistors worklike a pair of switches-when one is closedor on, the other is open, or off. But before wediscuss how our flip-flop works, let's review afew fundamentals of transistor operation.

The first is that a negative signal on thebase of an NPN transistor becomes a positivesignal at the collector. A positive signal onthe base becomes a negative signal at the col-lector. An NPN negative signal applied to thebase of a PNP transistor turns it on and apositive input signal turns it off.

Take a look at Fig. 1, a simplified sche-matic of a flip-flop along with oscilloscopephotos of signals. When you connect the bat-tery a negative transient signal appears on the

Fig. 1-Schematic ofbasic flip-flop (astablemultivlbrator). Pulses onbase of Q1 (photo atleft) are positive be-cause they're from leftplate of C2 when it dis-charges. Waveform atcollector of Q2 Is col-lector voltage. Flattenedpart near the horizontalaxis is due to the satu-ration of Q2 when it Isin the full -on condition.

base of Q I . QI is now turned on and it sendsa positive signal to the base of Q2. This turnsQ2 off. And as this happens, Q2 sends a nega-tive signal through C2 back to the base ofQ I . Everything is reinforced, that is, QI isdriven further into conduction and Q2 isdriven further off. When Q1 is fully on, thevoltage at its collector is a steady negativeDC. All this happens very quickly, then theaction of the circuit comes to an abrupt halt.

Things don't stay off for long. Eventually,C 1 and C2 come into action again. Remem-ber, capacitors Cl and C2 block DC but willpass a rapidly -changing signal. Such a signalexists when Q1 and Q2 are turning on or off.However, Cl and C2 have been charged bythe voltage at the collectors of Q I and Q2.After Q1 and Q2 have switched, C 1 and C2begin to discharge and reverse the on -off stateof Q1 and Q2.

Consider C2. After Q2 is completely off,C2 begins to discharge and the positivecharge, or voltage, on its left plate is appliedto the base of Q I . This turns Q1 off whichsubsequently turns Q2 on. The circuit thengoes through the same cycle again. Q I andQ2 switch on and off at a frequency de-termined by the value of the components.

C/

0

0 +

FEE084CKE---

10

1-;

FLIP FLOP FLIP FLOP FLIP FLOP FLIP FLOP

Use large capacitors or increase resistancein the base circuit, and you'll reduce thespeed.

Build the flip-flop on a piece of perforatedcircuit board or masonite as in Fig. 3. Notethe values to use for RI, R3, C2 and C3 inthe chart below the schematic in Fig. 2.When power is turned on, you should hearabout a 400 -cps tone. The tone sounds con-siderably fuller than that of a sine -waveoscillator because it is rich in harmonics.

You can produce a lower or higher -fre-quency tone by installing a 1-megohm po-tentiometer (R6) in place of RI. Also install

a 4,700 -ohm resistor (R5) in series with R6to limit Q1's collector current.

To convert the circuit to an electronictimer, just put a 30 p.f electrolytic capacitorin parallel with C3 with the polarity shownThis, in conjunction with R6, slows down thespeed to about a tick every 30 seconds.

To make a flasher, remove the speaker andconnect the lamp (P1) and R4 as shown inthe schematic. (Also change components in-dicated in the chart in Fig. 2.) When poweris applied, the bulb will flash on and off. Tovary the speed, use a higher -value resistor forR1. (If RI's resistance is too low, the lamp

PARTS

B1-9 V battery (Burgess 2U6 or equiv.)C1-.1 µf, 200 V tubular capacitorC2-.02 irf tubular capacitor or 10 id, 15 V

electrolytic capacitor (see chart)C3-.01 itf tubular capacitor or 30 if, 15 V

electrolytic capacitor (see chart)P1-No. 49 pilot lamp (2 V, 60 ma) and holderQ1, Q2 -2N408 transistorResistors: 1/2 watt, 10% unless otherwise indicatedR1-270,000 ohms or 10,000 ohms (see chart)R2-10,000 ohmsR3-150,000 ohms or 10,000 ohms (see chart)

111

0

R5

S/

OPERATION RI R3 C2 C3

SPEAKER 2T0K 150K .02p1 .010LAMP 10K 10K 100 3001

LIST

R4-100 ohms, 1 wattR5-4,700 ohms (see text)R6-I megohm potentiometer (see text)Si-SPST toggle or slide switchSPAR -3.2 -ohm speakerTI-Output transformer, primary: 2,000 ohms;

secondary: 3.2 ohms (Lafayette 33 R 3701 orequiv.)

Misc.-No. 14 tinned copper wire, perforatedphenolic board (7 x 4 in.) flea clips, alligatorclip

P/LAW

NIFig. 2-Schematic of flip-flop audio generator or lightflasher. Values of starred parts depend on whether cir-cuit is to be flasher or audio generator. To vary audiofrequency, install R5, R6 instead of RI. 55 limits Ql'scurrent when all of R6's resistance is out of circuit.

11

P FLOP FLIP awl FLIP FLIP FLOP FLIP

will remain on since its filament cannot cooloff between flashes.)

Monostabk Multivibrator. Another im-portant flip-flop is the monostable. When apulse is applied to the circuit QI and Q2 gothrough one on -off cycle then just sit therewaiting for another pulse. The monostableresponds to nearly any triggering signal andis valuable where such signals may differ instrength or duration.

You can observe this type operation withthe Ian* circuit and with C3 removed. Re-moving C3 opens the closed feedback loop

between Q I and Q2 and prevents continuousoperation. When power is applied to the cir-cuit, the lamp should remain on. Now dis-connect the end of R I that goes to thenegative power buss. Tap the free lead of R Iagainst the negative power buss to apply atriggering signal to Ql. You'll see that nomatter how you tap the resistor lead-for along or short time period-the lamp goesfrom on, to off, to on again. And it repeatsthis in a manner relatively independent ofhow you apply the trigger signal.

-H. B. Morris.

MID

tom

Fig. 3-Parts can be soldered to fleaclips inserted into the perforated

board's holes. install two piecesof No. 14 tinned copper wire along

the top and bottom edges of theboard to provide convenient tiepoints and to serve as the pos-

itive and negative voltagebusses. We didn't use an

on -off switch. Simply clipthe positive lead fromthe battery to the lowerbuss to apply power.

PI

S/ILI/WM

roN12/P0401

0,71 &ono& MY/

12

CI

THREE -way bulbs havean annoying habit of burning ou-

a lot faster than ordinary bulbs. Kceptract of how frequently you replace them,

convert the statistics into dollars and cents andyou'll store your three-way lamps in the aqic. We

don't know why the bulbs are so short-lived 'put theymust be toing something wrong.There's a way to beat the conspiracy. Replace theswitch in the lamp socket with our solid-state dimmer,then use a conventional 150 -watt bulb. Did yicu get that?A complete solid-state full -wave dimmer bu It right inthe bottom of an ordinary lamp socket!Compare prices: a 50 -100 -150 -watt three-xay bulb

costs about 700. An ordinary 150 -watt bath costsabout 350. In no time at all the saving in

bulbs will pay for the dimmer, which willse: you back about $5. And a cirn-

mer will lengthen the life of thebulb because the dimmer appliescurrent gradually. A switchsends a surge of currentthrough the bulb. Besidesall that, our In -A -SocketDimmer is an interest-ing project in itself.

By BERT MANN

RI

TCI

Fig. 1-Diagram shows layout of components inarea of socket formerly occupied by the switch. Put

spaghetti on all leads and wrap tape around TC1's case.

Fig. 2-Dimmer schematic. Because TC1 is bidirectional, it conducts both halves ofAC cycle (full wave) in a way similar to two SCRs connected front-to -back (inverse- A2parallel). Phase -shift network (111,R2 and Cl) causes neon lamp N1.1 to generate vary-ing -amplitude pulses which are fed to the gate of TC1. Pulse amplitude determineshow much of each half of AC cycle TCI conducts. When Ri's wiper is at top, pulseamplitude is greatest. TC1 conducts almost entire AC cycle and lamp is brightest.

Figure 2 shows the complete dimmer cir-cuit. All components except the plug fit inthe socket. Note that there is no on -off switchbecause R1 turns off TC1 and the bulb. TC1is a bidirectional thyristor made by RCA.RCA's name for the device is a Triac. It con-ducts current in two directions, as might twosilicon controlled rectifiers connected front -to -back and in parallel. The range of illumi-nation control is from off to full on.

Construction. We built our dimmer in apush-thru socket, as is found in most lamps.We suggest you build your dimmer in thistype socket because the construction of aturn -knob socket is somewhat different andour illustrations would not be suitable.

There's not a bit of extra space availablein the lamp socket; therefore, you must usethe miniature components specified in theParts List. To avoid shorts and to eliminate

TCIBOTTOM

VIEW

shock hazard, assemble the dimmer exactlyas shown in Fig. 1, using spaghetti on everylead longer than '/8 in.

First, remove the socket from its metalcase or shell. Look down into the base andyou'll see two screws. Loosen them until theswitch falls away from the base. If rivets areused, drill them out. Take care not to losethe tab-the part of the socket that touchesthe bulb's bottom contact.

Replace the screws (or rivets) with No. 2or No. 3 by 1/2 -in. -long machine screws.Fasten together the fiber insulator disc andthe threaded base. Cut one screw at the nutbut do not cut the other because you con-nect one side of the AC line to it.

Solder a 2 -in. piece of No. 22 solid in-sulated wire to the center -contact tab, insertthe tab into the fiber insulator disc, then slipthe base into the cylindrical cardboard in -

14

l',41;t4

C

Fig. 3-If rivets were used to hold the socket to-gether, drill them out. Discard switch assembly (inhand) but save all other parts. Cut short thescrew (No. 2 or No. 3, 12 in. long) indicated bypencil-the one opposite the center -contact slot.

PARTS LIST

C1-.1 µf, 200 V ceramic disc capacitor(Sprague type TH-P10, Allied 43 0 6606. 780plus postage; not listed in catalog)

C2-.02 µf, 200 V microminiature papertubular capacitor (Aerovox type P95ZN,Lafayette 34 C 7327)

NU-NE-83 neon lampR1-50,000 ohm miniature potentiometer

(Lafayette 32 C 7359)R2-2.700 ohm, 1/2 watt, 10% resistorR3-12,000 ohm, 1/2 watt, 10% resistorTC1-Triac, RCA type 40485 (Allied $3.14

plus postage; not listed in catalog)

sulator. Fit the insulator into the socket case.Temporarily install RI in one of the twoswitch slots in the socket case. Check thatneither of the two base mounting screws istouching RI's case (if they are, the socketcase will be connected to the AC line).

If possible, rotate the base so RI is cen-tered between the screws. (If necessary lateron, apply a drop or two of silicon-rubberadhesive between the base and the cardboardinsulator to prevent the base from turningwhen the bulb is inserted.) Route the leadpreviously connected to the center -contacttab against the insulator and connect it toRI's right and center lugs, as shown. Care-fully remove this assembly from the socket.

Cut off the tab on TC1's case and file theedge smooth. Because the A2 lead of TCI isconnected internally to TC1's case, the casemust be wrapped with a turn or two of tape.

Place NL1, pointing toward the base, di-rectly against TC1. Making the shortest pos-sible connection, connect one of NL1's leadsto the G lead from TCI. Then connect leadAl to one side of the AC line cord and to oneof Cl's and C2's leads. Before installing anyother components, solder one side of the ACline cord to the long base -mounting screw.Finally, install R2 and R3.

Limitations and Use. The dimmer canhandle a maximum of 150 watts. Do not usea larger bulb. Rotate RI full counterclock-wise and plug in the line cord. Slowly ad-vance RI until the bulb comes on. (The bulbwill light at a higher brightness level than itsminimum brilliance, obtained when you turnR1 counterclockwise from full on.)

Safety Check. To make certain there's noshock hazard caused by a short to the socketcase, connect one lead of an AC voltmeter(set to indicate more than 125 VAC) to thecase and connect the other lead to a ground.such as a cold -water pipe. Turn the dimmerfull on and note whether the meter indicatesabout 117 VAC. Then reverse the power plugand look for an indication. If the meter failsto indicate either way, all is well. If the meterindicates voltage, there is a short.

Is

Hallo

YOU1)0 IT?

By CHARLES GREEN, W3IKH

Why let sloppy -looking projects

embarrass you when the touch

of the pro is but six steps away?

THE man who said, "Whatever isworth doing at all, is worth doing

well." could have had constructionprojects in mind. It takes only a littlemore effort, but think of the feeling ofpride you'll get from a well-built proj-ect like that amplifier above. The ex-pert's look is just a matter of planningahead with these steps in mind:

Layout the chassis Cut the holes Make brackets and shields Mount the components Wiring Mark the chassis.

STANDARDCHASSIS

OPENEND

CHASSIS

OPENENDCHASSIS

MINIBOX

Four basic chassis are available in unpaintedaluminum or gray hammertone.(available in steel for heavy projects) has four sidesand bottom plate. Open-end chassis have sideaccess. Miniboxes are best for small projects.

the Scrounger that you shouldon the air or an evening venrummaging through a ninkbort

I uning capacitor 4.large one) of a serapacitor. Modify itmoving the tricapacitor stmh t canpurchafor I 1

C:111:11

the tiryeachat r -

Ix mireone hole li ii

evenly. spaced n.I hen cement thkglue in household cc

To scale the chassis, measure the width of thephoto (dividers and ruler) and the chassis. Ifthe photo is 2 -in. wide and the chassis is 6 -in.wide, multiply all of the photo dimensions by 3.

Tape graph paper on the chassis then layout center lines for all holes and identify the hole diameters. And it's a good idea to use a compass tcdraw circles the same size as each of the holes.

After drilling all holes, use a taper reamer toenlarge the tube -socket holes to 34i -in. dia. forthe socket -punch lead screw. Use the reamer forpotentiometer and ariable capacitor holes, too.

Use a centerpunch before drilling and you'll findthe lob a lot easier. Always start off with a smallbit and work your way up. A block under thechassis will prevent the metal from bending.

Socket holes should be cut without removing thegraph paper. You have to put a lot of muscle in-to the wrench so hold the chassis firmly. UseI 8 -in., 34 -in. and 5s -in. dia. socket punches, re-spectively, for octal. 9 -pin and 7 -pin sockets.

Socket mounting holes can be located by usingthe socket itself as a template. Place all othercomponents on the chassis then mark their mount-ing holes on the graph paper. Do not mount anyof the parts until all holes have been drilled.

17

Remove burrs from all holes with either a tapered ream-er, a triangular or a half -round file. Grasp thetool loosely and slant it in hole. Then clean up theedge of the hole on both sides of the chassis.

Large holes can be cut easily with a nibbling tool. Ifsuch a tool isn't available, back up the chassis with awood block and drill a series of small holes. Then use achisel or hacksaw blade to remove metal between the holes.

Chassis lettering can be done easily with a label -maker that prints on strips of adhesive plastic. Youcan also use decals or dry transfer lettering sheets.

Small brackets and shields can be formed byusing a heavy mallet and a vise. Drill allmounting and component holes before bend-ing. And make sure that you use untempered metal that will bend without cracking.

1.

Those Multiplying CellsAM a camera, push the shutter release

and the exposure is perfect every time.Send a space vehicle into orbit and forgetabout the batteries dying since operatingpower will come from the sun. The magiccomponent that makes all this possible? Thesemiconductor photocell.

The examples we've used rely on two basictypes. The first is a photoconductive photo-cell. Since it works just like a variable re-sistor, it also is called a photoresistive cell.The cell's resistance changes in inverse pro-portion to the intensity of the light striking it.The greater the light, the lower the resistanceand vice versa. Thus, the cell is used to con-trol current flow in a circuit.

The other type is the photovoltaic photo-cell. Also called a solar cell, sun battery orsimply a self -generating cell, it generates cur-rent when exposed to natural or artificiallight.

The operation of both photocells is basedon semiconductor action. The material usedin the photoconductive cell is cadmium sul-phide (CdS). The cell's construction and op-eration are shown in Fig 1.

The cell is made by depositing a thin layerof cadmium sulphide, to which electrodes areattached, on a ceramic base as shown in A.During the manufacture of the cadmium sul-phide, an impurity is added to convert it toa N -type semiconductor-a material rich infree electrons.

PROTECT/YE071100,

CADMIUMSUIP11/0E

CERAMICBASE

ELECTRODES

1/611T

%,%,,,,S \\NS, V

(A)

If there's no light on the cell electron ac-tivity is low and the resistance of the cadmiumsulphide, and consequently between the ter-minals, is high.

When light energy in the form of photonsstrike the cell, the cell absorbs energy andelectron activity increases. Assume that thecell shown in Fig. 1-B is connected to a bat-tery. Free electrons now will be attracted tothe positive side.

As the electrons move to the positive ter-minal they leave behind what are called holes.The holes, which have a positive charge, areattracted by the negative terminal.

In other words, light energy stimulates cur-rent carriers within the cell. The more light,the greater the number of carriers and thegreater the current flow. The effect of this,the increase in current, is the same as wouldbe produced by a variable resistor connectedto the battery. Lower the resistance and cur-rent will increase. The cell, load and batterycan be connected without regard to polaritysince the action will take place in either di-rection.

The operation of the photovoltaic or solarcell is more complex. It's made of P -typeand N -type semiconductor materials (eitherselenium or silicon) as shown at the left inFig. 3. This is the way this cell works:

When the P and N semiconductor mate-rials are joined, a potential barrier region isbuilt up. When the cell is in darkness, holes

PROTON

ELECTROK1

N -TYRESEM/COROUCTOR

MATER/41

(B) (C)

OLE \\ACds

CELLLOAD

BATTERY

Fig. 1-Diagram A shows photoconductive coil construction. In B, activity of free electrons is increasedby light which causes them to be attracted by positive external voltage. Holes left behind are at-tracted by negative side. This results in a current flow whose magnitude is determined by light intensity.

19

Those Multiplying Cells

and electrons (circled plus and minus signs,respectively) move toward the junction be-cause of their mutual attraction. This move-ment eventually stops.

When light strikes the junction, photonsforce the electrons and holes across the junc-tion, causing electron -hole pairs to be formed.The activity caused by the combining of theelectrons and holes produces a difference inpotential between the electrodes, which is in-dicated by the meter as a current flow.

To witness the operation of a photovoltaiccell, connect one to a meter as shown in Figs.2 and 3. You now have a simple meter thatmeasures light intensity. The cell to use is anInternational Rectifier type B2M (Allied 7U 876). Connect the cell's red lead to thepositive meter terminal and the black leadto negative terminal. If the meter is a 0-100µa DC microammeter, it will indicate ap-proximately the intensity of light falling onthe cell in foot-candles per square foot. Thetable below converts current to light level.

Meter indication(microamperes)

Foot-candles /square foot

0 0

20 6.440 12.8

60 26.080 52.0

100 104.0

The B2M cell can also be used to power asmall transistor radio. The cell's output in

PHOTON ()HOLESQ aten/OHS

j--r-//NCT/ON

#POTENT/AL

BANK/ER RE6/01/

'METER

Fig. 2-Experimental setup to demonstrate photo-voltaic -cell light meter. You could mount the meterand cell in cabinet for portable applications.

sunlight is approximately 0.4 V at 2 ma. Ifthis voltage is too low, connect cells in seriesto add their voltages. Higher currents can beobtained by connecting several cells in par-allel. A series -parallel arrangement boostsboth voltage and current.

In electronic parts catalogs you will findother cells (silicon) whose output is greater.Some have nearly a 1-V output at over 20ma in sunlight. The International Rectifiertype S5M, for example, has a 0.6- to 0.85-Voutput at 18 to 25 ma.

A cadmium -sulphide photoconductive cellcan be connected in a circuit in the sameway as a variable resistor. But there is oneimportant thing to keep in mind-maximumapplied voltage. If you wish to connect thecell in a 117 -VAC circuit, choose a cell witha 250- to 300-V rating. Lower -voltage cells

Fig. 3-In diagram of photovoltaic cell at left, holesand electrons are caused by light to cross potentialbarrier region and combine. Minority carriers which are created pass through the junction and are ac-tually the current developed by the cell. Diagram at the right is of photovoltaic -cell light -level meter.

it*

O

20

Fig. 4-Photoconductivecell connected in serieswith two 9-V batteriesand a sensitive DC re-lay can be used to turnon lamp as darknessapproaches. Make surecurrent drawn by exter-nal circuit does not ex-ceed rating of the con-tacts. A 10,000 -ohm po-

et tentiometer connectedin series with the re-lay can be used tocontrol the sensitivity.

can be used safely with batteries. The cell'sratings and other important details, such asresistance under light conditions, also willbe listed in parts catalogs.

Another value that must not be exceededis the cell's maximum power dissipation inwatts. If it's not stated in the catalog, it canbe determined by multiplying maximum volt-age and current ratings of the cell.

A simple setup in which a photoconductivecell can be used to control a relay directlyis shown in Figs. 4 and 5. This circuit is use-ful for applications like triggering an alarmor turning on a lamp as when darkness ap-proaches. The cell to use is Clairex typeCL -602 (Allied 7 U 460). It's resistance isabout 3,000 ohms in bright room light andmany times higher in darkness. The relay,(Lafayette Stock No. 99 R 6091) is a sensi-tive DC type (5,000 -ohm coil) that closeswhen the coil current is about 2 ma.

TO CONTROLLEDCKT

With these specs you and out that the re-lay requires 10 volts for its contact to close.Here's how: Using the formula E=IR, wefind that .002 x 5,000=10 V. Since the pho-tocell's resistance is 3,000 ohms when illumi-nated, it will have a voltage drop across it.Thus, if the required current is 2 ma (.002 A)and 'cell resistance 3,000 ohms, the voltagedrop across the cell will be 6 V. Therefore,about 16 V is required to operate the cir-cuit. Two 9-V transistor -radio batteries inseries will do the job.

When using this circuit with 117 VAC, youshould enclose it in a cabinet so you don'tget a shock. Also, an AC relay that will han-dle higher voltage will have to be substituted.However, a better approach is to use a step-down transformer to reduce line voltage toa safer level. Then long leads may be run tothe photocell and other parts with safety.

-H. B. Morris -I-

CdsCELL

/SY

Fig. 5-Schematic of photoconductive -cell control device. Sixteen volts is required to provide currentto cause relay contacts to close. Clairex cell we specify (not shown above) can handle up to 300 Vand can, therefore, be used with AC relay in, line -operated circuits. Cell handles up to 75 milliwatts.

21

ADD A

MONITOR HEADTO YOURRECORDER

By LAWRENCE GLENN

WHAT a blow it is to discover you haveworse than nothing on that tape you

made at the last party! Sure, the level indi-cator was moving and what you may haveheard via something called the monitor jackled you to believe you'd have a good record-ing.

But these clues were misleading becausethey did not reveal whether anything actu-ally was being put on the tape. At best, theyindicated simply that the recorder's elec-tronics was working.

To know with certainty whether you havea tape and how good it is, your machine musthave a monitor head-a third head whichlets you listen to the recording a fraction of asecond after it's made.

There's no need to trade in or scrap yourpresent recorder for a more expensive ma-chine that boasts three heads since you canadd a monitor head to your present machine.

Fig. 2-Nortronics TG -7 tape -guide post, in-dicated by pointer, insures that the tape willwrap around head gently and oxide won't rub off.

Fig. 1-Head mounted at corner of deck. Tape -guide post goes in bracket marked X to keep theoxide from being rubbed off due to tight wrap.

And a four -track monitor head on an oldhalf-track machine will let you play prere-corded stereo tapes, to boot.

The job may take a little ingenuity sinceall machines are not the same as the one weshow here. Matter of fact, the mountingjust may be quite simple because you don'thave to get involved with the existing headmount. The new head is mounted on thedeck itself-the biggest problem may be find-ing space for it.

If your recorder is an older model-thelarge let's -not -crowd -things type, you'll haveno trouble finding an extra square inch or soon the deck for the monitor head. The four -track head we installed is a Nortronics No.1001 (Lafayette 28 C 5715). The head andits mount are supplied with installation in-structions.

If your machine is one of those new com-pacts on which there isn't an extra inch of

Fig. 3-Completed deck installation. Connect-ing block attaches cables to head. Adhesive inthe grommet keeps the cables firmly in place.

Fig. 4-No room on deck means you'll need a Nor-tronics 1.-S (Allied 15 A 8796) bracket. Installit so that the head assembly is even with deck.

deck space you'll have to add the head out-board.

Whether you go inboard or outboard avoidtight, right-angle wrap -around by using atape -guide post (Nortronics TG -7, Lafayette28 C 5761)-a polished metal pole that posi-tions the tape for gentle wrap around thehead.

Using a Nortronics Type QK adjustablehead -mount assembly (Allied 15 A 8891 S)you'll have no problem positioning a tapeguide since the mount is predrilled for besttape -guide position.

For deck mounting, simply install the headmount in any convenient spot. If you haveto go outboard, mount a Nortronics L-5 L -bracket (also Lafayette 28 C 5762) on theside of the recorder as shown in Fig. 4 andthen screw the head mount on the bracket.

Pass leads from the head through a smallgrommeted hole drilled in the deck. You'll

Fig. 5-Leads from extra head can be brought outto jack in side of recorder's cabinet. A four -trackhead will require a three -circuit phone jack.

Fig. 6-Completed outboard installation. Again,a Nortronics connectca is used to attach cablesto head. Don't forget adhesive in the grommet.

probably be tight on space so push all theleads under the deck and then fill the grom-met hole with an adhesive. The leads shouldbe connected to a two -circuit jack mountedon the side of the recorder cabinet. The moni-tor -head output should be fed into the tape -head or magnetic -cartridge input on yourstereo amplifier.

For optimum performance, the monitorhead must be properly positioned. The heightof the head must first be set so the head iscentered behind the tape. If a tape guide isused it also must be positioned correctly.

Finally, the mount's alignment screw-the one that pivots the head in an arc-must be adjusted to get the head in perfectazimuth alignment. This is accomplished byadjusting a screw while monitoring a tape forbest high -frequency response. Again, detailedalignment instructions are supplied with thehead and mount. --8-

Fig. 7-Mount assembly has several provisionsfor head alignment. Screws permit adjustment ofthe height, azimuth and tilt from perpendicular.

SUPER

SPEED

STROBE

CAN

STOP

THIS

ACTION!

AND

THIS!

20

150'

100

60

402

ova:

By JIM KYLE, K5JKX A DROP of milk strikes a surface. The eye andan ordinary strobe flash see nothing but a blur.

But the 1/10,000 -sec. flash of El's Super -Speed Strobe freezes theaction and the milk drop turns into a crown shape in the magnificentphoto shown at the bottom of the opposite page. A stream of waterfalling into a graduate becomes an arresting still-life in the upper photo.

These spectacular photographs could have been taken with a com-mercial strobe-but only with one manufactured a dozen years ago,not with a modern model. Those early models, though fast, were bulky,

had high operating voltages and cost plenty.As strobes developed over the years, size and cost decreased. But,

unfortunately, a price was paid for this-flash speeds decreased. Today.ordinary strobes have speeds that range from about 1/1,000 sec. to1/2,500 sec.

High-speed photography does not require the expensive bulky strobeequipment of yesteryear. The Super -Speed Strobe proves this. Its powerpack is 4 x 5 x 6 in. and it is not much heavier than a dozen or so rollsof film. Best of all, its cost is low. Less than $50 should put it in

your hands.The Circuit. Before we build it, let's take a quick look at the circuit

in Figs. 6 and 7. The power supply is a conventional half -wave voltagedoubler that furnishes 450 VDC to storage capacitor C2. To achievethe 1 /10,000 -sec. flash speed, C2 must be a computer -grade electro-lytic capacitor. The type specified in our Parts List is not expensive($1.12) and you must not substitute an ordinary electrolytic for it.

The charge on C2 is applied to the flash -tube through a connectingcable that should not be longer than 10 ft. After power is turned on,capacitor C3 charges to 225 VDC through R1 and the primary of T2.When the shutter contacts close (SOI's or SO3's contacts are shorted).

Fig. 1-Strobe consists of 4 x 5 x 6 -in. power pack and 63/4-in.-dia. flash head. Flashhead plugs in socket at top of power pack. Socket below is for sync cable to camera.

25

Fig. 3-View of under-side of chassis showswiring to sockets andswitch on cabinet coverplate. Negative lug onC2 is connected to chas-sis with a strap madeof scrap aluminum. Be-fore closing cabinetcheck to make sure lugson Si and SOI don'ttouch edge of chassis.

SUPER SPEED STROBE

Fig. 2-View of chassis shows how transformer ismounted. Capacitor C2 is held in place with home-brew strap using screws which hold terminal strips.Leads to cover should be at least 6 -in. long.

C3 discharges through T2's primary, causingT2 to produce a 3-ky pulse. This pulse is ap-plied to the flashtube and fires it.

Resistors R3 and R4 (Fig. 6) are a voltagedivider for the neon ready -light (NL1). Ca-pacitor C4 causes NL I to blink, indicatingthe unit is ready to fire again. The lower C4'scapacitance, the faster the blink rate. C2'srecharge time and the time it takes NL1 tostart blinking after a flash normally are un-der three seconds.

Construction. Start off with the power sup-ply, which is built on a 2 x 41/2 x 31/2 -in.aluminum chassis as shown in Figs. 2 and3. Mount transformer TI and connect itsleads but do not cut or solder them. Apply117 V to TI's primary and measure voltageacross the red secondary leads. Now inter-change the connections of the 6.3-V (green)leads and measure the voltage again. If it'shigher, solder the leads in place. If the volt-age is lower, reverse the connections of thegreen leads and solder them. Now solder Ti'sother leads.

Next, install CI, RI and R2. When con-necting SR 1 and SR2. hold their leads with

Fig. 4-Back of flash head. Reflector is supplied with holes predrilled for red. white and blackleads from flashtube and screws that hold terminal strip and T2. Detail sketch at eft shows howa 11/4 -in. screw is installed through the reflector to hold the terminal strip and the back cover.

long -nose pliers to prevent heat damage.Mount Sl, SO1 and SO2 on one of the box'scover plates and install a grommet for theline cord. Install the line cord then mountC2 (next to T1) on the top of the chassis (Fig.2) with a homemade clamp. Watch the po-larity when connecting C2. After wiring toSI , SO1 and SO2, attach the chassis to thebox's other cover plate.

Fit the flashtube's glass lead stems throughgrommeted holes in the reflector then put two6-32 x 1 -in. long machine screws throughthe pre -drilled holes (13/4 -in. centers) in thereflector. Run nuts on both screws then slipT2 on one of the 1 -in. screws. Put a ter-minal strip and nut on the other screw asshown in Fig. 4 and 5. (Use a fiber washeron both sides of T2 so you don't damage itswindings.)

When connecting the flashtube's leads tothe terminal strip shown in Fig. 4, use careor you'll break its glass stems. Now installR3, R4, C3, C4 and NLI.

Drill holes in the reflector's back coverfor the cable and for S03. Attach PLI tothe cable making sure the 450-V lead goes

Fig. 5-Back of flash head. Threaded spacer onterminal -strip mounting screw is Ws in. long.The threaded spacer that holds T2 is Vs in. long.

to pin 1 and the 225-V lead goes to pin 2.Put threaded spacers on the ends of the two1 -in. screws and tighten them so that therim of cover touches the back of the reflector.Attach the cover with 6-32 x 1/4 -in. screws.

Checkout. Plug in the line cord and turn

12

44

Fig. 6-Flash head schematic.When shutter is tripped C3 dis-charges through T2's primary.72 steps up pulse to 3 kv. caus-ing flashtube to fire. The SO3 isoptional (shown at lower left).

IPLI C3 -=

+I(

S03

12RED

C4

RED

WHITE

R3

BrITIC

FLASHTUBER4

Fig. 8-For portable operation build thispower supply, which uses 225-V batteries.However, keep in mind that batteries costalmost 58 each and their life will be short

Fig. 7-Power supply. For greater light output but slower speed, add C6 and S2.For high-speed operation leave S2 open. Always turn power off before closing S2.

2.8

1'

Flashtube voltage vs. time -average of 50 measure-ments made with a Tektronic 545-A oscilloscope.

SI on. Ready -light (NL1) should begin toblink within 15 seconds. If it does not, con-nect a jumper across either SO l's or SO3'scontacts and see if there's a flash. If there is,the trouble is in NLI's circuit and is not seri-ous. If you don't get a flash, turn everythingoff and check your wiring. Before you touchanything, discharge C2. If you touch it whenit's charged the shock could be fatal!

Using The Strobe. Connect the sync jackon your camera to the strobe at either SO Ior S03. Operation is the same as that of anyother strobe but exposures are different. Inorder to achieve such high speed we've sacri-ficed light output. As a result, the power rat-ing of the stroke is 5 watt -seconds.

The extremely fast flash affects film differ-ently than does the longer flash of conven-tional strobes or flashbulbs. This means nega-tives will have less contrast. Thus, film shouldbe developed from one and a half to twotimes the normal time for comparable con-trast.

The photographs on the first page of thisarticle were taken with a Rolleiflex and Tri-Xpan film, using an ASA guide number of 20.The shot of the graduate was made with apiece of white translucent screen 6 in. behindthe graduate. The strobe light was placed one

4s'----tTUBE FIRES

LIGHTIN FIRST

OUTPUT1/10Q000 SECOND

END,--TRIGGER

OF

PULSE

LIGHT ENDS

SECONDVOLTAGE

DROPS

AT

TO 50

1/10,000WHEN

350-

1

50

020 40 60 80 100

TIME - MICROSECONDS140

foot behind the screen and the camera was12 in. in front of the graduate.

The shot of the drop of milk was takenwith the camera and light side by side 12 -in.away. In both cases, the diaphragm was setat f.22. The film was developed in Micro-dol-X for about 22 minutes. -$

PARTS LIST

131, B2-180/225 V battery (Eveready 492 orequiv.) Optional, see Fig. 8.

C1-8 of, 450 V electrolytic capacitorC2, C5-40 µf, 450 V computer grade electrolytic

capacitor (Mallory, Lafayette 30 R 5738 orequiv.)

C3-.1 At 600 V tubular capacitorC4-.1 tif to 4µf (metallized paper, not electro-

lytic) 200 V capacitor. See text.C6-525 if. 450 V energy -storage electrolytic

capacitor. Sprague FF-1, Allied 15 Z 726,$13.50. Not listed in catalog.

NL1-NE-2 neon lampPL1-Double contact plug. Amphenol 80-MC2M.

Lafayette 32 R 1920 or equiv.)RI, R6-22 megohm, th watt, 10% resistorR2, R5-300 ohm, 10 -watt resistorR3-1.5 megohm. % watt, 10% resistorR4-3.3 megohm, % watt, 10% resistorSIA, SIB, S1C-3 pole, DT slide switch

(Lafayette 99 R 6166 or equiv.)S2-SPST switchS3A, S3B-DPDT switch

S01, S03, SO4-Chassis mount AC socket(Cinch -Jones 2R2 or equiv.)

S02, S05-Double contact chassis connector.Amphenol 80-PC2F. (Lafayette 32 R 1919 orequiv.)

SRI, SR2-Silicon rectifier; 750 ma, 400 PIV(Allied 39 U 669M or equiv.)

Tl-Power transformer; secondaries: 125 V15 ma. 6.3 V @ 0.6 A. (Allied 61 U 410 orequiv.)

T2-Flashtube ignition transformer; primary:180 V, secondary: 3-5 kv. Amglo ST -25, Allied7 Z 914, $2.50 plus postage. Not listed incatalog.

FLASHTUBE-Amglo HD -1, Allied 9 Z 380, $9.50plus postage. Not listed in catalog.

Misc.-Reflector: Amglo AR -365-0, Allied 6 P 637,$8.00 plus postage (not listed in catalog);flash head back cover: Amglo R -65C, Allied6 P 636, $6.75 plus postage (not listed incatalog); 4 x 5 x 6 -in. utility box (Bud AU -1029or equiv.); 2 x 4% x 3% (Bud CB -1625 orequiv.); terminal strips; wire.

29

FM Guitar BroadcasterBy LAWRENCE GLENN IMPORTANTthing swingers must have to really make thebig scene these days is a guitar. Most every-where you go-the beach, picnics, a ski re-sort, parties-you'll hear the instrumentgoing all the time. The fad has grown tre-mendously.

Many guitar owners lay out quite a bit ofextra cash for an amplifier to soup-up the in-strument's volume. But EI's FM GuitarBroadcaster gives your guitar the big soundand saves you money to boot. The Broad-caster puts out a low -power signal in the FMbroadcast band. This means you can use yourstereo system (provided it includes an FMtuner or receiver) as the guitar's amplifier.

By operating your own popular-musicbroadcasting station (the Broadcaster has aninput for a mike over which you can makeannouncements) you'll always be a step aheadof the other strummers in the crowd. About$10 worth of parts and an hour or two ofeasy work will put you on the air.

Other possibilities? You can serenade thegirl next door even when it's raining. No needto stand under her window and get wet. Justsit in your favorite arm chair and strum. She'llbe able to pick you up on her FM radio.

If you're really good at playing and singing,

you might take the guitar to the beach or lakeand serenade the crowd through their FMportables.

Heart of the Broadcaster is a low -powerFM transmitter module. It's a prewired, en-capsulated FM transmitter and modulator towhich you simply connect a contact mike,battery and switching facility for a mike.

You mount the components on a piece ofperforated phenolic board, or other plasticmaterial, then install the board inside theguitar, as shown. Of course, we don't rec-ommend you hack away at a $100 guitar. Wesuggest you install the transmitter in the $20guitar you knock around at parties.

ConstructionOur transmitter is built on a 21/4- x 3 -in.

piece of perforated board. Note that theboard is only large enough to hold a singlebattery clamp for one penlight cell. One cellwill produce a range of up to about 50 ft.For slightly more distance, connect two cellsin series and use a larger board to accom-modate a larger battery holder.

Before mounting any components drillfour mounting holes-one at each corner ofthe board-for #6 screws. (The mountingscrews should be self -tapping.) Then, on

Broadcaster is built on21/4- x 3 -in. piece of per-forated board. Modelshown has one penlitecell, which will give arange of up to about 50ft. For a slightly greaterrange. use larger board,two penlite cells andinstall a double batteryholder. Note in pic-torial, wire connectedto D on module (FM1).It is an antenna and itslength determines op-erating frequency. Besure to get connectionsto S2 correct. Ml shouldnormally be connectedto module. When S2 ispressed, crystal mikeplugged in 11 is con-nected to the module.

top of the guitar, position the board anomark an outline of it with a pencil or scrib-er. Since hand capacity will detune thetransmitter, position the board as far aspossible from the normal playing positionof your hand and arm.

Drill a 1/2-in.-dia. hole 1/8 in. in from thescribed line at one corner. Using a fine -tooth -blade keyhole saw-preferably a sheet -metalblade-cut out the opening for the trans-mitter board. Note in the photo of the guitarthat the corners are angled so there's supportfor each mounting screw.

Next, position the contact microphone(M ) on top of the guitar near the soundhole and drill a #28 hole for Ml's mountingscrew. When drilling the hole, keep in mindthat the contact mike will be turned overwhen it is mounted inside the guitar. MountMI by passing it through the transmittercutout. Keep MI near the transmitter holeor you'll have to remove the strings in orderto get your hand inside the guitar.

Now assemble the components on the per-forated board. Remember that there will be1/4 in. of wood under the board, so keep thecomponents at least Vs in. in from the board'sedges. First mount the single or double bat-tery holder. Then mount mike jack J1, push-button switch S2 and power switch Si,

Switch Sl is a miniature DPDT type (usethe one specified) whose unused lugs shouldbe cut off. Using a thin layer of silicon rub-ber adhesive, such as GE's RTV or Silastic,

31

PARTS LIST

131-1.5 V penlite cell (see text)FM1-FM transmitter module: Cordover Type

FMG-1. Carl Cordover & Co., 104 LibertyAve., Mineola, N.Y. $3.50 plus postage

J1-Phono jackMI-Crystal contact microphone (Lafayette

99 R 4516)SI-DPDT subminiature toggle switch

(Lafayette 99 R 6162); Modified, see textS2-Miniature SPDT pushbutton switch

(Lafayette 99 R 6218 or equiv.)Misc.-Perforated board, battery holder,

guitar, crystal microphone.

FM Guitar Broadcastercement the FM module to the board, posi-tioning it up against SI and the batteryholder. If you don't cement the FM moduleagainst the switch and holder you'll have toadd wire to the module's leads.

Cut off the excess shielded cable from thecontact mike (M1), leaving about 3 in. pro-truding from the hole. Connect the mike tothe circuit and install the assembly in theguitar. If you don't like the color of theboard, paint it with quick -drying model paint.

Tune UpThe Broadcaster's output frequency is

around 100 mc. Place an FM radio near theguitar, or place the guitar near your stereosystem's FM receiver. Turn on power withSI and tune the FM receiver for the deadcarrier being transmitted. Flick Si on andoff a few times to make certain you've tunedin the right signal.

If the Broadcaster's signal interferes with

Use a fine -tooth -bladekeyhole saw to cut outa section (under hand)of the guitar for thetransmitter board. Posi-tion the contact mikeclose to the cutout andmount it inside the gui-tar with its shieldedcable passing throughthe transmitter hole. Asingle screw holds thecontact mike in place.

MIKEFM1

Schematic of Broadcaster. SI turns on power. S2is shown connecting contact mike to module. WhenS2 is pressed, It connects external mike to module.

an FM station, change its frequency by add-ing a small length of wire-about 1/2 in. ata time-to the module's antenna (wire D).Increasing D's length will raise the frequency.

Now play a tune. You should hear theguitar in the receiver. Plug a mike into J1,press S2, and speak into the mike. Youshould hear yourself, or a horrible squeal( feedback) if the receiver's volume is toohigh. If the Broadcaster fails to operate,check S2's wiring. If the connections are re-versedwhile the contact mike will be switched onwhen you press S2.

For convenience, especially if you planto announce all your numbers, the announcemike may be taped to the neck or frame ofthe guitar enabling you to keep both handsfree at all times. To operate the mike yousimply press S2. When S2 is released, you'reall ready to play.

Okay, standby; 10 seconds. You're on -the -air! -4-

32

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Construction of Osulloscooe Construction of Multimeter.

33

It took 15 minutes to install 2% x 61/4 x 8 -in.Lafayette HB-525 transceiver. Rig is so smallthere's legroom for passenger in middle seat.

Only two No. 8 self -tapping screws were requiredto install bracket for typical solid-state trans-ceiver. You start holes with punch, then drill.

The ratill WayBy AL TOLER REMEMBER the good

old days of mobile CB in-stallations? The dashboard bent under 20lbs. of weight, there were firewall braces,power cables almost as thick as your fingerand the rear seat was out in the gutter so theantenna cable could be snaked through thetrunk. It was great fun.

Then there was the antenna -bracket holein the fender that ended up costing you $100at trade-in time. Or maybe there was a rearbumper mount that was sheared off when theguy behind you kissed bumpers as he pulledout. And did you ever notice how a CB rigbecame a yard wide when you tried to findspace for it under the dash? Or was itstrapped to the driveshaft tunnel where itwould cut your ankle whenever you movedyour right foot from brake to gas pedal?

All these irritations now are history. Themodern mobile CB transceiver-completewith antenna and cables-can sit on the palmof your hand. It requires no new body holesand can be installed without power tools. Allyou need is a punch, open-end wrench, screw-driver and possibly a soldering iron.

First Things First. We'll start with thetransceiver. Solid-state rigs no longer arehigh -price, second-rate performers. A mod-ern solid-state rig, such as the Lafayette HB-525 we show being installed here, contains

Secure transceiver with two gimbal -bracket screws, After removing existing auto -radio antenna, reconnect power cord to any hot wire under dash, move with sandpaper all dirt and rust on under -attach antenna cable and the rig is ready to go. side of fender to assure good ground connection.

to badiell ut *a etaall the important features of the big tubejobs. It has full 23 -channel crystal -controlledcoverage in both the transmit and receivemodes, delta tuning, squelch, a modulation -boost circuit, and the new PA feature. Bestof all, solid-state rigs are priced competitivelywith tube rigs.

You can squeeze a solid-state transceiverinto almost any car-even a sports job.Mounting takes three steps: punch two holesin the underside of the dash (you don't needan electric drill) secure the rig's mountingbracket with two No. 8 self -tapping screws,splice the power cable into any hot lead (suchas the cigarette lighter) under the dash andthe job is done.

CB Antennas Made Easy. A modern CBantenna is even easier to install. There areseveral dual-purpose, CB/ AM antennasavailable. These antennas, such as the An-tenna Specialists M-103 and M-143 or Lafa-yette's 99 C 3060, work both as an auto -radioantenna and as a CB antenna.

They are made specifically to fit in an ex-isting fender or cowl hole; absolutely no body

Attach connector on cable from CB/AM coupler toantenna. A locking bracket snaps into positionwhen the antenna base passes through the hole.

work is needed. Our diagram below showshow they work. When fully extended thelength of the antenna is around 46 in. Ap-proximately 8 in. below the top is a loadingcoil for CB operation. The coil, consistingof relatively few turns, has virtually no effectat the broadcast frequencies; therefore, thefull antenna length-which just about equalsa standard AM antenna-picks up the AMbroadcast signals.

So as far as CB signals are concerned, theantenna is resonant and most sensitive at CBfrequencies. Since the car itself is part of theantenna system, the length of the antennasection above the coil is made adjustable toallow fine tuning of antenna system.

The Magic Coupler. Most natural questionis how does one keep the auto -radio fromshorting out CB signals and vice versa? Theanswer is a CB/AM antenna coupler (sup-plied with the antenna or optional) which isconnected between the antenna, the autoradio and the CB transceiver.

Our schematic on the next page shows atypical CB/ AM coupler-there might be

ADJUSTABLE -LENGTH TIP -11.

27 -MC LOADING COIL --a.

TELESCOPINGSECTIONS

UNIVERSAL COWL MOUNT

COAX CONNECTOR

APPROX.46 IN.

TO CB/AN COUPLER

Combination CB/AM antenna has a universalmount and is no longer than average auto -radio an-tenna. Top loading coil resonates system to 27 mc.

35

71te few Way

k Adam at Yota

Tighten the lock nut on antenna mount with open-end wrench. Do not use pliers. Combination CB/AM antenna is ready to go since it is factory tuned.

Coupler connects single antenna to auto radioand CB transceiver. Incoming signal splits at A.RI keeps transmitter output out of auto radio.

slight variations but the theory is the same.The signal from the CB antenna is fed to pointA, where it sees two paths. One is a series -resonant (at 27 mc) path to the transceiver.The other is a high -resistance path to theradio. Since a series -resonant circuit has alow impedance at the frequency to which it'stuned (LI can be tuned to 27 mc), the CBsignal takes the path of least resistance andgoes to the transceiver input. At broadcastfrequencies, the small value of Cl appearsas a high impedance compared to RI so thebroadcast signals are blocked from going tothe transceiver and go to the radio.

During transmit the C 1 -LI path still is alow impedance; therefore, the transmitter'senergy goes without losses to point A whereit sees the low -impedance of the antennaor the high impedance (500 ohms) of RI.Therefore the signal goes to the antenna.The CB/ AM coupler is efficient and there is

A slight adjustment in the length of the antennasection on top of the loading coil might be re-quired to minimize the antenna system's SWR.

virtually no loss at 27 mc.Installing the CB/ AM Antenna hardly

could be easier. Remove your existing an-tenna and its cable. Pass the antenna leadfrom the coupler up through the fender orcowl hole and connect it to the new antenna.If the hole is too small to pass the coax con-nector attached to the coupler's cable, cut offthe connector, pass the cable through theholes and reinstall the connector. This is alot easier than trying to enlarge the cablehole in the fender. Fit the new CB/ AM an-tenna into the hole, tighten the nut and theantenna is installed.

Connect the remaining coupler cables tothe CB transceiver and the radio. Since mostsolid-state transceivers are factory tuned(usually with sealed tuning adjustments) thetransceiver is ready to go as soon as the con-nector is screwed tight. Generally, the an-tenna can be tuned up with an SWR meter.

Connect an SWR meter between the trans-ceiver and the coupler and adjust the top sec-tion of the antenna for minimum SWR. Theadjustment has a narrow range so don't ex-pect to see a large variation in SWR. As ageneral rule an SWR of 2.5:1 or better, isdesirable. Finally, tune the car radio to matchthe antenna. All car radios have a smalltrimmer capacitor located near the antenna -input jack. Tune in a weak station near thehigh end of the band and adjust the trimmerfor maximum volume-0-

Olt

36

C4)

CRYSTAL -CONTROLLED SW SIGNAL GENERATORBy LAWRENCE GLENN

THE short-wave bands are as jammed as a discotheque's dance floorthese days. With no big holes anywhere, you either tune to a station's

exact frequency right off or waste hours in dial twisting. But with a pre-cisely calibrated receiver, tedious station -hunting becomes a thing of thepast.

While a better -quality, expensive signal generator is capable of doinga reasonably accurate alignment job on your receiver, few experimenter -grade generators have the necessary stability and accuracy.

Most SW receiver alignment (or calibration) procedures require you toskip back and forth several times between the high and low end of eachband. Rare is the experimenter -grade generator that can be reset to, say,exactly 20 mc. But our generator puts you right on frequency every timebecause it's crystal controlled. Sure, it takes a handful of crystals to coverall the bands on your receiver but at least you'll have the equipment to getthe maximum calibration accuracy your receiver is capable of.

The generator is designed specifically for SW receivers. Its frequencyrange is from I to 20 mc on fundamentals. The circuit provides an outputrich in harmonics. This means that a crystal can be used to provide morethan one spotting frequency. For example, using a 2-mc crystal, the gener-ator will deliver harmonics at 4, 6 and 8 mc. Naturally, the higher the har-monic the lower the output. Though 20 mc is the recommended upper limit,a 14-mc crystal will produce a harmonic output at 28 mc. (The oscillatorcircuit is designed for fundamental crystals.)

To prevent feeding too great a signal to the receiver (alignment shouldbe done with the minimum usable signal level) our model's maximum out-put level is approximately 100,000 /iv. However, if you really need a bigsignal, reduce the value of R3 to increase the output level to 2 V (at 1600kc ) . R3 should not be less than 560 ohms.

To permit easy spotting of the signal and to enable you to align by

37

CII

SIA

R2

C4R3

)1 WAN

RI

CS

LI R6

R5

'OUTPUT LEVEL

C6

02L20 R7 4

RIO

9

CE1

Ril S2 RC12 C13

MODULATION0

R13 R12

R

S3

C7

BI

OLORDOT

01,02 03Fig. 1-Signal from RF oscillator Ql is combined with signal from AF oscillator Q3 in mixer Q2. 119controls modulation level; ft7 sets output level. Lowering R3's value will increase ouput to 2 V.

ji

=CIOCUT OFF

CRYSTAL CONTROLLED

SW SIGNAL GENERATOR

adjusting for maximum audio output, an ad-justable -level modulation signal at approxi-mately 1 kc is provided. The modulator canbe turned off if you don't need it.

The generator also can be used as an accu-rate frequency spotter. For example, supposeyour favorite SW station is R. Ivorienne(Abidjan, Ivory Coast) on 11820 kc. Thissignal hardly gets out of Africa's back yard,let alone into your antenna. How can youfind it on a crowded band? Simple. Get acrystal cut for 11820 kc and put it in the gen-erator. To find or spot R. Ivorienne you sim-ply turn on the generator, tune the receiverfor the generator's signal, turn off the gener-ator then wait for the voice of the Ivory Coastto come in.

Our model has three crystal sockets-twoinside the cabinet and one on the front panel.The panel -mounted crystal socket permits anycrystal to be installed immediately in the cir-cuit. Within the allowable interior and front -panel space there is no limit to the number of

PARTS LISTB1-9 V battery (Burgess M6 or equiv.)Capacitors: 15 V or higherC1-1,200 AO silvered micaC2-75 AO silvered micaC3-.05 irfC4-250 AOC5-.001 AfC6,C7,C11,C12,C13-.01C8-.005 idC9-.25 irfCEO -160 irf electrolyticJ1-Phono jackL1,L2-1 mh RF choke (J. W. Miller 70F103A1.

Allied 54 D 1885, 750 plus postage. Notlisted in catalog)

Q1,Q2-2N274 transistorQ3 -2N2613 transistorResistors: '/2 watt, 10% unless otherwise indi-

catedR1-1,000 ohmsR2-220,000 ohmsR3-4,700 ohms (see text)R4-560 ohmsR5,R6-470 ohmsR7,R9-500 ohm linear -taper potentiometer

with SPST switchR8-68,000 ohmsR10-2,200 ohmsR11-470,000 ohmsR12,R13-4,700 ohmsS1A,S1B-2 pole, 3 position, non -shorting

rotary switch (Mallory 3223.1)S2,S3-SPST switch on R9,R7SO1,S02,S03-Crystal sockets (see text)Misc.-3 x 8 x 6 -in. cowl -type aluminum

Minibox (Bud SC -2132. Allied 42 A 8686 orequiv.), knobs

31

Qt

Fig. 2-While it is possible to mountall components on top of perforatedcircuit board as shown, we installedthe following parts on the underside:capacitors C243,C5,C7,C8; resistorsR1,113,114,R5,R6,R8,R11,}112 and R13.

Fig. 3-Photo of top of board showslocation of components. Note howmost of the resistors are mounted onend. Cutout in upper right corner isfor battery. Cutout at lower leftcorner of board is for output jack Jl.

built-in or external crystal sockets you canuse.

Crystals can be purchased ground to virtu-ally any frequency from Texas Crystals, 1000Crystal Dr., Fort Myers, Fla. 33901 and In-ternational Crystal Mfg. Co., 18 N. Lee,Oklahoma City, Okla. Since a crystal's priceis determined by tolerance and holder, wesuggest you write to each company for a cata-log then select what you need. We recom-mend Texas Crystal's FT -241 or FT -243holders or International Crystal's FA -5 hold-ers as they are low in cost running from under$2 to roughly $6, depending on frequencyand tolerance. When ordering, be sure tospecify parallel -resonant crystals.

While some overtone crystals, such as CB

crystals, will work in the generator, keep inmind that the indicated overtone frequencygenerally is not an exact multiple of the fun-damental frequency. For example the funda-mental output of a 27-mc third -overtonecrystal will not be 9 mc (1/2 of 27 mc). Itwill be slightly lower.

Construction. The generator is built in theU -section of a 3 x 6 x 8 -in. cowl -type Mini -box. All parts values are critical; no substitu-tions should be made.

To avoid a parts jam, with resultant im-proper operation, the three circuits (AF os-cillator, RF oscillator, mixer -modulator) arespaced widely on a piece of perforated circuitboard. Since there is enough room inside thecabinet we suggest you follow the pictorial

39

Fig. 4-Controls from left to right are outputlevel, crystal selector, modulation level. Largercabinet permits more front -panel crystal sockets.

CRYSTAI-CONTROLIED

SW SIGNAL GENERATOR

and photographs and do not crowd the com-ponents together. Similarly, install on the un-derside of the board those components notvisible in the photo of the top of the board inFig. 3. Don't put them atop of the board.

Cut a piece of perforated -board so it willjust about cover the bottom of the cabinet.Then trim the board about in. all aroundto clear the cabinet's top -cover mountingflanges. Cut a notch out of one corner of theboard for the battery and another near outputjack J 1.

Before mounting any components, installall of the panel controls, crystal sockets andJ1. Mark the board directly under each con-trol to make certain you do not install anycomponents under the controls.

Crystal sockets S01, SO2 and SO3 shouldmatch the crystal used. In general, the TexasCrystal type SSO-1 socket is preferred sinceit matches the FT -243 and FT -241 crystalholders.

Note in Fig. 3 that several resistors aremounted on end. (For the sake of clarity weshow them mounted flat in the pictorial.)Either flea clips or Vector T28 terminals canbe used for tie points. To avoid soldering heatdamage to the transistors, do not trim theirleads shorter than 3/4 in. and use a heat sink.

Connections to the crystal sockets aremade by soldering No. 22 solid wire to theterminals and passing the wires down and upthrough holes in the perforated board. Theother ends are soldered to selector switch S1after the board is installed in the cabinet. Ifyou want to use more than three crystal sock-ets, substitute for SI a two -pole rotary switchhaving the appropriate number of positions.

Final Assembly. Slide the perforated boardunder the controls and secure it to the cabi-

Fig. 5 --Inside of generator. Note location of bat-tery and how it's held in place. Also notice howboard is raised above bottom of the cabinet.

net with screws at four corners. To preventthe tie points and parts on the back of theboard from shorting to the cabinet, place a1/4 in. spacer or stack of washers between theboard and the cabinet at each screw.

Checkout. Do not plug in any crystals yet.Set output level control R7 and modulationcontrol R9 counterclockwise so their switchesclick off. Connect the battery's negative leadto the generator and connect the positive leadto the positive terminalset to indicate 10 ma or higher. Connect themeter's negative terminal to the battery ter-minal on S3. There should be no meter indi-cation. If there is, check for a wiring error.

Apply power by turning R7 clockwise; themeter should indicate about 5 ma, though itmay be somewhat higher or lower. If themeter indicates more than 10 ma look for awiring error in the oscillator (Q1) or themixer (Q2) circuit. Next, apply modulatorpower by advancing R9; the meter indicationshould rise 1 or 2 ma. If the total meter indi-cation exceeds 10 ma look for a wiring errorin the AF -oscillator (Q3) circuit.

Connect .11 to your receiver's antenna ter-minals through a section of thin coax such asRG58/ U and plug a crystal into any of thecrystal sockets. Set S1 to the appropriate po-sition and tune the receiver until you pick upthe generator's signal. Then check the opera-tion of R7 and R9. Adjusting R7 will vary theamount of modulation.

Receiver Alignment. Since short-wave re-ceivers are all aligned differently, it's best foryou to follow the alignment instructions sup-plied with your model. Because our generatordoes not supply a 455-kc IF signal, you sim-ply align the IF transformers by peaking themon a signal fed to the antenna terminals -0-

te

THE audio scene is changing again. Aftera few years of watching speaker enclo-

sures diminish in size, we're beginning to seethem get bigger. And as the trend continues,an old standby-the large bass -reflex enclo-sure-is coming back into the limelight.

The bass -reflex design is not at all new. Asthings go in the world of audio, it has grownquite a beard since it was patented in 1932.Properly designed and tuned, a bass -reflexspeaker system is capable of delivering excel-lent sound.

Tucked away on page 103 of Lafayette's1967 catalog is a bass -reflex enclosure kit.Available in either a high- or low -standingdesign, it sells for $32.92, unfinished. Its vol-ume is about 5 cu. ft. Though Lafayette saysthe cabinet is made of plywood, it actually isflakeboard covered with white -birch veneer.

The 20 C 0122WX (the stock number)

A SIZABLESPEAKER

SYSTEM

Lafayette Lowboy

kit is supplied with a variety of mountingboards to accommodate almost any speakersystem. Choices are single- (full -range). two -or three -speaker systems. The three -speakersystems can be made up with a 12- or 15 -in.woofer, 6- or 8 -in. midrange and a varietyof tweeters.

The system we built and tested used a$22.95 12 -in. woofer (stock No. 21 C 4720).a $6.50 midrange (stock No. 21 C 4718), a$9.95 dome -lens compression tweeter (stockNo. 99 C 6250) and a $14.95 three-waycrossover network (stock No. 99 C 0022).All told, our system cost $87.30. A 15 -in.woofer costing $23.95 (stock No. 21 C47I9W) is available but we do not recom-mend it for reasons to be discussed later.

What was it like to put together a cabinetwhose parts were said to be precision cut sothey would fit together snugly? The first set

Biggest problem in cabinet assembly is at top corners. Note in photo at lett that excess stock between dadoand mitered edge must be removed before assembly. In center photo, glue is shown being applied to splinegroove. In photo at right, the spline is inserted in the groove, after which it is tapped gently into place.

co +10

+5

0W

2 5O

tf)10(4,tk -15

20 30

15 -INCH WOOFER

50 100 200 500 1KC

FREQUENCY (CPS)

A SIZABLEOf instructions sup-plied with the kit was

SPEAKERvague and somewhatconfusing. We found

SYSTEMit was easier to as-semble the cabinetby referring to an ex-

ploded -view drawing. But the instructionsheets have since been revised and, except forone omission, they are satisfactory.

The omission covers splines (thin woodstrips) which are furnished with the kit. Theyare not mentioned nor are they shown in thedrawings. It would not be surprising, there-fore, for an inexperienced builder to throwthem out since they look like strips of scrap.They are used to align the mitered joints andto prevent the glued surfaces from shifting.

Assembly wasn't difficult. You place thetop panel face down on a flat surface and at-tach the cleats. Spread some glue ( supplied)in the joint, then draw the cleat tight withthe screws. Put some glue in the splinegrooves and insert the splines. The top andsides are assembled with screws. The bottomand sides are screwed together without cleats.

Ready to be closed up. Crossover network ismounted in bottom of cabinet. Midrange- andtweeter -level controls are in cabinet's rear panel.

5 KC 10KC 20KC

Curve in color shows responseof system with 12 -in. woofer.Black curve is response with15 -in. woofer. Poorer low -endresponse with 15 -in. woofer isdue more to speaker than cab-inet. When size of port is re-duced to 21/2 x 5 in.. responsedown to 40 cps with 12 -in.woofer is improved and is bet-ter than with the 15 -in. woofer.

Tuffiex acoustic material is attached withstaples to the top, one side and the rear panel.

We checked the enclosure with two differ-ent 3 -way speaker systems, using the same8 -in. midrange speaker and tweeter with a12 -in. and a 15 -in. woofer. The crossover net-work was wired for 700 cps and 3,000 cps.

Impedance curves for the two woofers re-vealed that the port size was correct for the15 -in. woofer but too great for the 12 -in.woofer. There were no instructions for tuningthe cabinet and there is no convenient wayof reducing the size of the port. ( Lafayettehas advised us that tuning instructions willhe included with future kits.)

Response measurements of the systemwere made with a PML type EC -61A cali-brated condenser microphone. The curvesshown with this article indicate what we con-sider mediocre low -frequency response withthe I5 -in. woofer. But this was due primarilyto the speaker and not the enclosure. Despitethe fact that the enclosure was not at firsttuned for the 12 -in. woofer, much better per-formance was obtained with this speaker thanthe 15 -in. woofer. After we reduced the portsize to 21/2 x 5 in., response with the 12 -in.woofer was smooth down to 40 cps.

We found the 8 -in. midrange speaker to hetoo efficient for the woofer and tweeter andit tended to peak a hit below 600 cps. Bysetting the midrange level control at the 9o'clock position, we improved balance.

The tweeter displayed smooth, clean re-sponse out to 20 kc. The only fault we foundwith the tweeter (for use in this system) wasits 16 -ohm impedance. (The woofer and mid-range are 8 ohms.) However, we balancedthe tweeter by setting its level control at the3 o'clock position.

Three hours after starting construction weput the test equipment and tools aside andsat down to listen for a while. The sound wasgreat-no doubt about it-from the lowestbass right on out to 20 kc.

42.

BETTMANNARCHIVE

Electric cars were the cat's miaowaround 1908 when Kimball made the one

above. Drawing is Ford's idea for updating.

OF THE NEWELECTRIC CARSBy J. K. LOCKE

New batteries challenge the range, speed and cost of gasoline.

ONEDAY last fall in a Detroit laboratory, I watched physicist Neil Weber

hook the leads from a small electric motor to a pair of wires stickingout of a glass bottle the size and shape of a straightened -out banana. As hemade the connection, the motor began to spin.

The bottle was a new type of battery-a sodium -sulfur cell-developedby Dr. Neil Weber and Dr. Joseph Kummer of the Ford Scientific Laboratory.The battery (and the demonstration) looked ordinary enough. But this newsuper -power device, with 15 times the energy -storage capacity of the familiarlead -acid battery that starts your car, could be the most important develop-ment to hit the auto industry since the internal combustion engine. "Withthe invention of this battery," says Dr. Michael Ference, Jr., Ford vice-presi-dent in charge of scientific research, "we have surmounted one of the majorproblems-the lack of a sufficiently powerful battery-that must be resolvedbefore an electric vehicle can become a commercial reality."

Ford isn't the only company working to pack more kilowatts into smaller,lighter packages. Gulton Industries of Metuchen, N.J. (a firm known for its

43

work on the now -common nickel -cadmiumcell that powers most rechargeable cordlessdevices) has a super -high performance unitcalled the lithium cell. And two firms-Lee-sona Moos Laboratories of Great Neck, N.Y.(a firm that has pioneered in fuel cell work)and the General Atomic division of GeneralDynamics-are working on a new gadgetcalled the zinc -air battery.

The impetus for the high-energy effortstoward high-energy battery development hascome largely from efforts to do somethingabout a growing problem: air pollution.Scientists say the air -borne gunk-millionsof tons of it-hanging over our cities is re-sponsible for everything from running nylonstockings to corroding stone statues. Moreimportant, many authorities believe increas-ing pollution is a principal cause of the soar-ing death rates from respiratory diseases. Andmore than half the pollution, say the experts,comes from automobile tailpipes.

Electric automobiles, with exhausts as pureas so many spring zephyrs, seems the obviousanswer. The British have been working inthis direction for several years and a bill topromote research on electric autos has beenintroduced into the U.S. Senate. Electricautos are, of course, nothing new-they en-joyed considerable popularity from the turnof the century to World War 1-and electricutility vehicles are still used today.

But until now the electric has had one giantproblem: range. A car simply couldn't carryenough conventional lead -acid batteries todrive it more than 50 miles or so, althoughM. G. Smith of the Electric Storage BatteryCo., who make lead -acid batteries, has hintedthat his company might team up with othersin a joint development program.

The old standby lead -acid battery has whatengineers call an energy density of 10 watt-hours per pound (wh/ lb.). That means thatevery pound of battery can store enough en-ergy to put out ten watts of power for onehour. A fully -charged ten -pound lead -acidbattery, in other words, can light a 100 -wattbulb for one hour.

Nickel -cadmium batteries, widely used inrechargeable electric gear such as portabletape recorders, have ratings of about 15wh/ lb. Even the prohibitively expensive sil-ver -zinc batteries can store up to 50 wh/ lb.( Yardney Electric Corp. of New York, whomake them, have suggested renting the costlysilver, which is not consumed in use.)

All three of the new systems, by way of

- DILUTESULFURIC ACID

LEAD DIOXIDE

LEAD

DIAGRAM 1- LEAD -ACID CELL

HOW THE NEW BATTERIES WORK:

ALL OF THE new batteries-in common with older bat-teries-work by extracting electrical energy from a chemi-cal reaction. The familiar lead -acid cell (Diagram I) dem-onstrates the principle:

The negative electrode is made of pure lead; the posi-tive electrode is lead dioxide. The two are suspended ina dilute solution of sulfuric acid. In the solution eachsulphuric acid molecule splits into two positively -chargedhydrogen ions and one sulfate radical-a sulfur -oxygenion carrying a double negative charge.

A sulfate ion finding its way to the negative electrodewill combine with a lead atom to form a molecule of leadsulfate-and release two electrons in the process. Mean-while another sulfate ion and the two hydrogen ions, find-ing their way to the positive plate, will combine with thelead oxide to make lead sulfate plus water-this timedrawing two electrons from the electrode in the process.

The important thing about this process is that it is re-versible. Apply a reverse (charging) current and the nega-tive electrode turns back into lead, the positive one againbecomes lead dioxide and the partially depleted sulfuricacid comes back to full strength.

43

a

-SOLID CERAMICELECTROLYTE

7\ LIQUID SODIUM

H- LIQUID SULFUR

DIAGRAM 3-SODIUM -SULFUR CELL

44

NICKEL -FLUORIDE

OR NICKELCHLORIDE

LITHIUM

PROPYLENE CARBONATE WITHHEXAFLUOROPHOSPHATE

OR

DIMETHYISULFOXIDE (DMSO)WITH HEXAFUJOROPHOSPHATE(WITH NICKEL -CHLORIDE

ELECTRODE ONLY )

DIAGRAM 2- LITHIUM CELLClosest in operating principle to the feed -acid cell is

the lithium cell (Diagram 2). During discarge, a fluorideion from the electrolyte combines with ar atom of lithiumfrom the negative electrode to form lithium fluoride, simul-taneously freeing an electron. Nickel fluoride from thepositive electrode combines with two electrons from theexternal circuit to form pure nickel and two fluoride ions,which flow off in the electrolyte. The a ternate reactionusing a nickel chloride positive electrode is very similar.

The sodium -sulfur cell (Diagram 3) pulls a switch byusing liquid electrodes and a solid electrolyte. The liquidsodium (negative electrode) is contained in a ceramictube. The tube, in turn, is suspended in a bath of liquidsulfur (positive electrode). The ceramic material is theelectrolyte. The atomic structure of the ceramic isimpervious to liquid sulfur and liquid sodium. But it willlet sodium ions (sodium atoms with an electron missing)through. When the sodium ions combine with the sulfur

AIRCOMPRESSOR

00

00

00

on the other side of the ceramic sieve they form sodiumsulfide. But the sodium sulfide is incomplete-it has oneelectron missing, hence the positive charge. The other elec-trode is negative because of the electrons left behind bythe sodium hat has passed through the sieve.

The zinc -air cell is somewhat more complicated, as Dia-gram 4 shows. Oxygen (or oxygen -containing air, pumpedinto the electrolyte in this version of the cell through aporous nickel positive electrode) is ionized in the electro-lyte (potassium hydroxide) faking free electrons from thepositive electrode in the process. The oxygen ions travelto the negative zinc electrode. There, the zinc and oxygencombine, forming zinc oxide and releasing electrons.

The circulating electrolyte is vented (to allow excessair to escape) and filtered (to keep zinc oxide from clog-ging the cell). When the battery is recharged the zinc oxideis pumped back and electroplated onto the negative elec-trode once more as metallic zinc

0 00 0

0 0o

POROUS NICKELELECTRODE

ELECTROLYTE

ZINC ELECTRODE

FILTER

ELECTRO-LYTE

RESERVOIR

DIAGRAM 4- ZINC -AIR CELL

45

contrast, show promise of future ability topack in some 150 wh/lb.-15 times as muchas the lead -acid battery.

While all three of the new systems lookpromising, problems remain. The lithium bat-tery, for example, has been built only in smallsizes; scale -up will present engineering andproduction problems that must be solved be-fore it can be made into a commercial prod-uct. The sodium -sulfur battery must operatein the vicinity of 500°F. to keep the sodiumand sulfur liquid. Ford engineers think they'llbe able to design insulated containers to keepthe units hot for weeks at a time. Waste heat

Dr. Weber (left above) holds sodium -sulfur cellhe developed for Ford with Dr. Hummer. who sitsnext to model of 2,000 -watt battery. Prototypeof General Dynamics' zinc -air battery (below)was developed jointly with 14 electric utilities.

should keep temperatures high enough.The main drawback of the zinc -air battery

comes in designing auxiliary pumping andcooling equipment to make it work properly.Leesona Moos (who make zinc -air batteriesfor military electronics) have one novel solu-tion to the recharge problem. When the bat-tery runs down-that is, when the zinc platesare used up-operators will simply slip newones in. Only trouble with this technique foruse in automobiles is that putting in newplates costs more than recharging.

Some of the new super -batteries will beavaliable for use soon, however. A few of theLeesona Moos replaceable -electrode zinc -airbatteries are now on the market. The smallest(25 ampere -hours) is about the size of a tran-sistor radio and weighs less than two pounds.Largest one to date is smaller than a loafof bread (5 x 5 x 7 in.), weighs eight poundsand puts out 100 ampere-hours-as much asan automobile battery weighing some 40pounds. (Like any first -run item, it's expen-sive. A 12 V, 100 -ampere -hour battery costs$570. Large production runs would slashprices substantially.)

The General Atomic division of GeneralDynamics, together with a combine of 14electric companies helping to bankroll thework, will plow $150,000 into rechargeablezinc -air battery development work this year.The company has already built a 28 -kilowattprototype, and is getting ready to build onefour times that size. This second unit wouldbe powerful enough to run a delivery van.

To date. Gulton has built only a half-

pound, 18 -ampere -hour lithium battery. But,says Dr. Robert C. Shair, vice-president incharge of research, if some car maker wereinterested, a car -sized version would be readyquickly: "If some automobile companywould like to do it on a joint basis-if theywould engineer the car while we engineer thebattery-it could be done in a year."

Ford is predicting rapid development, too."We foresee no scale -up problems," says Dr.Jack Goldman, director of Ford's scientificlaboratory. "It should be a straightforwardengineering job. The first step will be a2 -kilowatt, 22 -pound unit, which will beready by this December (1967). Then scale-up to a size big enough to drive an automo-bile will take another year." Adds Dr. Fer-ence, "We have the money, the manpower,and the desire to move ahead as rapidly aspossible." 4-

2 Meters on 2 TubesWith this really basic receiver you can pull in a fascinating

mixture of local OMs and Novices on the most popular VHF band.

By CLARE GREEN, W3IKI IT'S a busy, friendly world up on 2 meters.The high frequency, 144 to 148 mc, means

mostly local contacts, though there are rare DX openings, when signals gohalfway across the country.

Regulars on 2 get to know each other well. There's a lot of local rag -chewing and some hams call the band a big party line. Though in mostareas 2 meters means phone operation, at times you can find a greatervariation in hamming-and hams-than anywhere else in the spectrum.All hams-Generals, Novices, Technicians, everybody-can operate on 2(it's the only band where Novices are permitted on phone) and practicallyanything that oscillates is allowed, including regular CW, modulated CW,unmodulated carriers, facsimile, TV, FM and RTTY.

You also will find a lot of 2 -meter inhabitants who know their onionsand who build their own equipment. Readymade rigs are relatively scarcewhen compared to 10-80 gear. That means a lot of home-brew equipment,which in turn means a fair level of technical competence because VHFcircuitry can be quite tricky and critical.

Besides hams being hams, you also will find CAP stations and MARSnets on and at the edges of 2 meters.

With our cooll 2 -tuber it's an easy matter to listen in on the band. Thereceiver sports a superhet front-end followed by a superregenerative de-tector. Two stages of audio drive a speaker. Headphones can be pluggedin to dig out those weak stations.

.-1410MPIAmmancimem."...,

I 'A

En117 Vic

Because the receiver operates from 144 to 148 me, placement of parts, especially around VI at the right.is critical. And it also is important to install the parts exactly where shown around V2. For the purposeof making things parts smaller than their real -life size.Note the cutouts in the chassis near J2 and between R11 and R9. The cutout at the left is for thespeaker frame; the cutout at the right is for the 23/4-in.-dia. pulley on the back of the slide -rule dial.Circle around T1 is 3/4-in.-dia. hole in the chassis through which leads (soldered on coil's lugs beforemounting) to Ti pass. As parts around VI and V2 are quite close, use spaghetti on the leads to pre-vent shorts. Detailed sketches of coils LI and Ti are shown on schematic on the last page of the article.

2 Meters on 2 TubesConstruction. Our receiver is built on a

7x11x2-in. aluminum chassis. After cuttingall holes, mount the components where shownin the photos and pictorial. Locate the posi-tion for TI's shield, then cut a'/4 -in.-dia. holein the chassis for the leads to the coil's lugs.Make cutouts on the front of the chassis toprovide clearance for the dial's pulley andthe speaker's frame.

Before mounting C4, make sure its shaftlines up with the dial pulley's hub. Alwaysuse lockwashers when mounting the terminalstrips, fuse holder, potentiometers and outputjack J2. Put rubber grommets in all chassisholes through which wires pass to preventthe insulation from being frayed.

The wiring and placement of parts in thefront-end and detector circuits are critical.

If leads are too long the receiver may tuneout of the band or may not work at all. Useshort, direct leads when installing all com-ponents. Slip spaghetti on all leads that crossor are near each other. Before mounting T1,solder leads to its lugs since it will be difficultto get to the lugs through the hole in thechassis after the coil is in place.

Alignment and Operation. Turn on the re-ceiver and allow it to warm up a few minutes.If a signal generator is available, set it foran 8-mc modulated output and connect it toJ1. With volume control R11 full clockwise,turn up regen control R9 until you hear thetypical superregen hiss. Adjust T1 for maxi-mum output. Set tuning capacitor C4 so thedial pointer is opposite 20 on the loggingscale.

Set the signal generator for a 144-mc mod-ulated output. Adjust L2 (starting with theiron core all the way in) until you hear thesignal. Set the signal generator for 145 me

tr

and tune C4 until you hear the signal. AdjustLI for maximum signal amplitude whilerocking C4 back and forth to keep the signaltuned in. Calibrate the rest of the dial withthe signal generator. We used transfer type tomark the dial's scale at 1-mc irrervals from144 to 148 mc.

If you don't have a signal generator, set

Best place to start con-struction is around VIat the right. Fit everypart in carefully andkeep leads short anddirect. Then work yourway left to Tl.V2 andthe power supply at theextreme left. Install con-trols, dial and speakerlast. lust becausethere's a lot of emptyspace doesn't mean youcan spread parts ouLKeep them tight aroundthe tube sockets. UseNo. 14 buss wire tohook the antenna con-nector at lower right toterminal strip near VI.

TVs slug -adjustment screw so it is 1/4 -in. outof the top of the form. Set Ll's and L2's slugadjustment screws so they are 3/8 in. out ofthe form.

Wait until evening when the 2 -meter handis most active and connect an antenna to J 1.(The best antenna for this receiver is a high -gain multiple -element beam.) With the dial

PARTS LISTCapacitors: 1,000 V ceramic disc unless otherwise

indicatedC1,C9-47 µpi C2,C3-4.7 µAiC4-3-15 ppf variable capacitor (Bud MC -1850.

Allied 13 Z 530; $1.82 plus postage. Not listedin catalog)

C5-10 1.10 C6-500 #11.(fC7,C8,C13,C15,C18,C22-.001 AlfC10-100 AO C11-.25 if 200 V tubularC12,C16,C19,C21-.005 ifC14A,B,C-50/30/20 jilf, 150 V electrolyticCI7-8 Af, 12 V electrolyticC20-.05 uf, 400 V tubularF1-1 A fuse and chassis -mount holderGIMMICK-Capacitor made of two turns of hook-

up wire (see text)A-Chassis mount coax connector (Amphenol

83-1 R)J2-closed-circuit phone jackL1,L2-0.1 j4hy adjustable RF coil (J.W. Miller

20A107RB1. Lafayette 34 R 8944)L3-1.72 jahy RF choke (J.W. Miller RFC -144. La-

fayette 34 R 8973)L4-1 mh 3 -section RF choke (J.W. Miller 4652.

Lafayette 34 R 8829)Resistors: V2 watt, 10% unless otherwise

catedR1-1 megohm R2-22,000 ohrritR3.R16-33 ohms R4-10.000 ohms

R5,R6,R12-4,700 ohmsR7-6.8 megohms R8,R10-120,000 ohmsR9-250,000 ohm linear -taper potentiometerR11-1 megohm audio -taper potentiometer with

SPST switch (S1)R13,R14-220,000 ohmsR15-100 ohms, 2 wattsR17-1,800 ohms, 2 wattsR18-15,000 ohms. 1 wattS1-SPST switch on R11SPKR-4-in., 4 -ohm speakerSRI-Silicon rectifier; minimum ratings: 500 ma,

400 PIVT1-1.7-5.5 mc RF coil (J.W. Miller B-5495-RF.

Lafayette 34 R 8715. Shield for above, J.W.Miller S-33. Allied 62 Z 571; 51¢ plus postage.Not listed in catalog.)

T2-Power transformer; secondaries: 125 V @ 50ma, 6.3 V @ 2 A (Allied 61 G 411 or equiv.)

T3-Output transformer; primary: 10,000 ohms.Secondary: 4 ohms. 5 -watts. (Allied 61 U 448or equiv.)

V1-6BL8 tubeV2-6AF11 compactron tubeMisc.-Slide-rule dial (J.W. Miller SL -16. Allied

60.090; $6 plus postage. Not listed in catalog),7 x 11 x 2 -in. aluminum chassis, 7 x 11 -in.aluminum chassis bottom plate, 9 -pin tubesocket, compactron tube socket, terminal strips.

4

R3 TI

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Receiver schematic. Signal from antenna and os-cillator V1B go to grid of mixer VIA; 13-mc mixeroutput goes to superregen detector V2A. Audio isfed to audio amp V2B then to output pentode, V2C.Wind 1 turn of #22 solid wire on LI between low-er lug and base. Space wire to prevent a short.

2 Meters on 2 Tubesset to 40 on the logging scale (145 mc), ad-just L2 until you hear signals. Adjust LI formaximum volume.

Most 2 -meter signals are polarized hori-zontally so vertical whip and ground -planeantennas will not be effective. However, you'llbe able to get good results with a TV an-tenna. In normal operation, turn up regencontrol R9 until you hear a hissing, then tunefor stations.

How it Works. Take a look at the sche-matic. Signals from the antenna are fed di-rectly to LI, which is broadly tuned to 145mc. The signals then go via Cl to the grid ofmixer VIA. Oscillator VI B, whose output iscoupled via the gimmick capacitor (twotight -wound turns of hookup wire) to V1A'sgrid, operates 8-mc below the incoming sig-nal. The oscillator is tuned by C2/ L2 andC3/C4.

The resultant 8-mc IF signal at VI A's plateis fed via T1 to the superregenerative de-

"

R14

9

2

R

C2I

20'

VIEWED FROM LUG ENO

BLU

O

REDIll

[PHONES]

2

SPust.

LI

Top view of chassis. Note cutouts in the frontfor slide -rule dial pulley and speaker frame. In-stall 7 x 11 -in. aluminum plate in chassis bottom.

tector, V2A. R9 controls regeneration.The detected audio signal is connected via

the low pass filter (RIO/C15) to volume con-trol RIO then to the grid of the first AF am-plifier, V2B. The amplified audio is fed byC19 to power amplifier V2C. The signal iscoupled by output transformer T1 to thespeaker. When phones are plugged into J2.the speaker is automatically disconnected.B+ and the tube heater power are suppliedby T2, SRI and the filter circuit comprisingR17, R18 and CI4A,B,C. -to

TUBE VOLTAGESPin I 2 3 4 5 6 7 8 9 1011 126BL8 80 -4.5 90 0 6.30* 100 0 0 -3.5 - - -6AFI I 0 150 0 58 0 -2* -1.7 72 2.3 132 0 6.3**

Measured wi h a VTVM. ±20% R9 full clockwi e. **AC

If the receiver doesn't work prop-erly, first thing to do is measurevoltages on tubes to turn up a wir-ing error or defective component.All voltages must be measuredwith a VTVM and not a VOM.

5i

Automatic Telephone Answerino SetYou'll never miss a phone call with our electronic secretary on the job.

By FRED BLECHMAN, K6UGT "HELLO, this is the Blechman residence. No oneis home right now. This s a recording. If you'd

like to leave a 4G -second message, please start it at the sound of the tone.B -e -e -p."

This is what you hear if you call when we are out. Forty seconds after thefirst tone you hear another tone, then a dick as the phone is hung up. Whenwe arrive home we are able to listen to your message as well as about 15 others.

Designed to be built for about $50, the Automatic Telephone Answering Set(TAS) will do the same job as commercial message recorders that might setyou back a few hundred dollars.

The TAS has been designed around two inexpensive battery tape recorders.One recorder answers the telephone with a pre-recorded message. The otherrecorder tapes the caller's message for 40 seconds.

The timing of all operations is controlled by a 1 -rpm motor which drivesfour poker -chip cams which in turn operate microswitches. Each microswitchcontrols a separate function. The phone is coupled inductively to the TASfor ring -sensing and message recording. Direct connections to the telephoneline are not necessary. The answering message is acoustically fed to the hand-set's mouthpiece.

How it Works. Take a look at Fig. 4, a schematic of the TAS. When thetelephone rings, a pickup coil (L1) near the telephone base, picks up thebell's magnetic field and feeds a signal tc the two -transistor ring amplifier. Arelay ( RY I) at the output of the ring amplifier then starts the 1 -rpm timing

Fig. 1-The ring ampli-fier is built on a smallpiece of perforatedboard which is mountedon the inside of thechassis' rear paneL Usespacers between theboard and the chassisto prevent parts fromtouching the chassis.

WO Mein Aunts Set

motor. During the third ring, cam 1, whichcontrols solenoid L2, turns and trips micro -switch Si which energizes L2. L2 lifts a

spring -loaded lever which latches (S6) thetiming motor and lets the telephone -cradlepushbutton rise. This "answers" the phone.

One second later recorder 1 is energizedby cam 2 which closed microswitch S2. Thisplays the pre-recorded answering messageinto the answering speaker (SPKR 1) whichis located underneath the telephone handsetmouthpiece. Recorder 1 stops after about 14seconds and the tone is started by anothermicroswitch, S4. The tone sounds throughSPKR 1 for a fraction of a second.

Next, recorder 2 records the caller's mes-sage via handset -earpiece coil L3. Thirty-seven seconds after recorder 2 starts, the tone

TOBP2

TOBPI

Fig. 2-Ring-amplifier schematic. Ring signal atphone is picked up by LI, fed via shielded wireto Q1, amplified and fed to Q2 which closes RY1.

sounds again, recorder 2 stops and 2 secondslater L2 is released. This causes the spring -loaded arm to press down the telephonecradle pushbutton. When L2 is released, RY Iis unlatched and the motor stops turning.

If you cannot obtain the tape recordersshown in our model, use any battery -operated

31 41 56

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0 91

TO 02-C

TO334 -3

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TO TS4-5

01.02

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TO 154-6TO TS4- 4

Fig. 3-Pictorial of ringamplifier. We used socketsfor transistors in our model,but you could solder Q1'sand Q2's leads directlyinto circuit. Flea clips willserve well as tie points.Sketches at the top shownumbers we have assignedto the lugs on relay RY1.

52

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Fig. 5-Underside ofcontrol chassis. Liberaluse of terminal stripssimplifies wiring andkeeps everything neat.Partially visible at bot-tom are tone generator(left) and the ring am-plifier (right) boards.

Automatic Telephone Answering Set

transistor tape recorders. But be sure theirmotors operate on 1.5 V and their amplifiersoperate on 9 V. These requirements are veryimportant as the TAS is designed to supplythese voltages only.

The schematic of the ring amplifier isshown separately in Fig. 2. The 1.5 V for therecorder's motors is obtained from a 2.5-V

Fig. 6-Underside ofcontrol chassis. Usespacers between thechassis and tone -gen-erator module and ring -amplifier circuit board.

transformer (T1), rectified (SRI), filtered(C4) and is controlled by S2 and S3 (cams 2and 3).

The power to operate L2 is obtained byrectifying (SR2) and filtering (C5) 117 VACand is controlled by Si (cam 1). Diode SR3suppresses arcing across S7A's contacts whenL2 is deenergized. Function switch S7A,B,Cis a 3 -pole 4 -position rotary switch, used formaking the master answering tape and toallow rewind and playback of each recorder

TO.

FROMTI

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FROMTI

TO 5d-9

01

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BP. .-1111111111,....

IrtmiSRI

153

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FROM 9,/POWERSUNNY

FROMMOTOR

TO

TO R

i4

independently of the timer and the solenoid.Pilot light NL2 comes on when power is ap-plied to the TAS. A green light (NL1) comeson when solenoid power is applied.

Since components are located in the cabi-net and on the chassis, a multi -conductorcable is used to connect the two. The cableis equipped with an 11 -pin connector (S01)to provide easy separation. Similarly, theshielded cables that provide power to the re-corders are connected to a single plug (PL2)

MICROSWITCHES ARE ACTUATEDAS INDICATED

"0' TIME

ON 3(7-.1..

5 SEC.,'

OFF

ON +5OFF +60

CAM NO. I(SOLENOID )

OFF

ON +6OFF +20

CAM NO. 2(ANSWER)

Fig. 7-Timing assem-bly. U-shaped bracketwhich supports drivemotor (upper right) andcam shalt is homebrew. Dimensions arenot criticaL Note thehubs which are gluedon all the poker chips.

that plugs in SO2 on the chassis. Diodes D2and D3 are necessary to DC -isolate the re-corders from each other. If you don't usethem you'll find strange interactions.

Construction. The ring -amplifier (Figs.1,2,3) can be built on a small piece of per-forated board. Be sure to observe properdiode and capacitor polarity. The value ofresistor R2 may have to be changed to pro-vide about 0.7 -ma drain from the 9-V supplywith no ring signal. A ring signal should

ON OFF

OFF

7=2 SEC.

I38'

ON +21OFF +58

CAM NO. 3(RECORD MESSAGE)

6'

ON18' 3 SEC.

1".

6°

+ 57+56

CAM NO. 4(TONE)

ON +20OFF +21

138*

I SEC (T) 6*Fig. 8-Cam dimensions. Make all cuts with a jewelers saw then use sketches to line up cams onshaft. Numbers in boxes below cams show time after motor starts that the cams should actuate theirassociated circuit. Cam I, for example, should turn L2 on after 5 seconds and off after $0 seconds.

55

DRILL THRU ZEROTIME ®.SWITCH ON

5 SECONDSSTANDARD COUPLINGCAM IWAreA

zs's---...(INCLUDES TWO 1/4SET SCREWS)

1/4" O.D. POLYSTYRENE

SOLENOIDL2

CAM 2ANSWER

/ Z/./, "4"14-I SECOND

I SECOND

2 SECONDSH=WE\TUBING (I/8" 1.D) CAM 3

RECORDCOUPLING r-CAM 4

BEEPTONE

POKERCHIP

CAM

FLAT LEAFN.O.

N.0W

CEMENT

MODEL AIRPLANEWHEEL HUBS

- WITH SET SCREW -ON BOTH SIDESOF CAM

BAEPNPD

APPROXIMATELYIe....AS SHOWN

MICROSWITCH MODIFICATIONNO

N.0

ALUMINUMBRACKET

0 10 20 30 40 50 600

ONE SEQUENCE

SECONDS

Fig. 9-Cam-timing sequence. Duration of time aswitch is on may change. Do not change the timeintervals between operations of the switches.

cause the current to rise to about 2 ma.Capacitor C3 is necessary to prevent relaychatter.

A flat telephone pickup coil must be used.Place it alongside the phone base, as shownin Fig. 13. During preliminary tests later,have someone call you several times to findthe best coil location for fast relay closure.Be sure to use shielded wire from LI to theamplifier to prevent random noise from trig-gering the amplifier and relay.

The frame for the timing motor and camsis made by bending a piece of aluminum intoa U shape, as shown in Figs. 11 and 12. Thedimensions are up to you. On one end mountthe motor. Add about a 6 -in. length of 1/2 -

in. dia. brass rod or tubing to the motor shaftusing a standard 1/4 -in. shaft coupling, modi-fied as shown at the top of Fig. 10. All youdo is push a piece of 1/4 -in. O.D. polystyrenetubing ( 1/2 -in. 1.D.) into the coupling thendrill two holes for the setscrews. The screwswill cut their own threads in the polystyrenetubing. The other end of the brass tubing fitsthrough a small hole in the far end of theU frame.

The cams are made from poker chips. Drilla 1/2 -in. dia. hole in the center of each pokerchip and cement a model airplane wheel huhto each side to the chip, as shown in Fig. 10.These aluminum hubs, sold in hobby shops,have a 1/2 -in. center hole and a setscrew.The setscrew hubs allow individual cam ro-tation for final sequence adjustments duringtesting.

Fig. 10-Miscellaneous construction details. Cou-pling at top connects motor and cam shaft. Dia-grams below show cam construction, microswitchmodification and construction of answering arm.

t1

56

47

1 RPMMOTOR

Figure 8 shows the cam configurationsand Fig. 9 shows the timing sequence in ourmodel. If you prefer to have a longer answer-ing message and shorter recording period,change the angular cutouts accordingly, re-membering that one second equals 6 degreesof rotation. Once set and tightened, the camsneed not be touched again.

The four microswitches are mounted on

Fig. 12-Control chas-sis. Transformer T1,used to provide powerto tape recorders' mo-tors is at right. 9-VPower supply is at up-per left of the chassis.

Fig. 11-Diagram shows loca-tion of timing assembly onrear of chassis. Refer to Figs.4 and 10 to determine con-nections to normally -open andnormally -closed lugs on micro-sulated from timing chassis.

sheet -metal brackets (Fig. 10) and adjustedlater on. The flat -leaf actuator of each micro -switch should be bent as shown in Fig. 10for better action. The timing blocks in Fig.9 show the times the cams should actuatetheir associated microswitches.

Note that for proper sequencing, cam 2must activate after cam 1. Cam 3 activates 1second after cam 2 deactivates. Cam 3 must

deactivate 2 seconds before cam 1 deacti-vates. Some latitude in timing and spacingcan be tolerated, but the sequence must be asshown. The position of the beep tone in thesequence is not critical, so long as it occursnear beginning and end of recording period.

Chassis Assembly. Remove the 9-V powersupply's bottom cover. Then drill three holesin it and install mounting screws and nuts;the latter will act as studs. Now replace thebottom cover. The extended studs are usedwith nuts to mount the power supply to thechassis. Mount the transformer on the topof the chassis using grommets in its leads'holes. Mount a 5 -pin socket (SO2) for the

Fig. 14-Other sideof cabinet showslocation of modeswitch S7, indicatorlamps and powerswitch S5. Note lo-cation of ring pickupcoil Ll. Detail ofcorner of cabinetmarked with the let-ter A is in Fig. 16.

58

Fig. 13-Cutaway ofcabinet shows locationof speakers and ear-piece -pickup coil L3.Drill holes in cabinet forspeakers and cementthem to cabinet. Puthandset in place beforecementing L3 to cabinet.

recorder power cables on the top of thechassis. Mount the timing assembly on thetop of the chassis.

On the back of the chassis (inside) mountthe ring amplifier, tone generator and insu-lated binding posts BP1-BP4. Make no con-nections to the chassis. Since a flat toroidalpickup coil (L3, left, Fig. 13) is not availablecommercially, you must make your own byrandom -winding 1,600 turns of No. 34enameled wire on a 11/4 -in. dia. form. Re-move the coil, tightly bind it with maskingtape and solder a shielded lead to the ends.The resistance of the coil should be about150 ohms.

Cabinet Assembly. Our cabinet was builtfrom 1/4 -in. plywood and held together withstrips of molding in the corners. Details areshown in Figs. 13 and 14. The telephonehandset holder is made from two woodenblocks. Drill small holes for the two minia-ture speakers (Fig. 13) and cement themto the inside of cabinet. Note in Fig. 10 thatthe latching pushbutton switch (S6) must bemounted so that it is pressed when the sole -

Fig. 15-Top view offront of TAS. Note loca-tion of blocks on whichhandset is placed. Alsonote the locations of thespeaker at the mouth-piece position and thehome-brew coil at theearpiece position (left).

TO NORMALLY -OPEN CONTACTS

TO PLI-10

TO PL1- I

TO PLI- 3

Fig. 16-Inside view ofcorner of cabinet re-ferred to in Fig. 14.Solenoid L2 specified inParts List is plungertype and requires dif-ferent installation. Besure solenoid pullsenable/disable armdown causing it to pressfirmly on switch 86.

noid pulls down the back of the enable/ dis-able arm.

The arm, by the way, is made from 1/4 -in.aluminum tubing. One end is flattened so itwill press down the phone's pushbutton tohang up the phone. The arm is pivoted on asmall screw held in a home brew sheet -metalbracket.

A short length of piano wire couples thesolenoid to L2. When L2 is energized it pulls

PARTS LIST

BI -1.5 V penlite cellBP1-BP4-5-way, insulated binding postsC1-50 pf, 15 V electrolytic capacitorC2-100 id, 15 V electrolytic capacitorC3-20 olf, 15 V electrolytic capacitorC4-1,000 pf, 15 V electrolytic capacitorC5-20 µf, 150 V electrolytic capacitorCAMS 1-4-Cams made from poker chips (see

text)CB1-1 A circuit breaker (Sylvania MB -315 Mite -

1 -Breaker. Allied 56 A 4075)01-03-General-purpose germanium diode (La.

fayette 19 C 4901 or equiv.)LI-Telephone pickup coil (Lafayette 99 C 1034

or equiv.)L2-Solenoid: 115 VAC, 1A -11/2 -in. stroke, con-

tinuous duty, 65 -oz. lift. (Guardian No. 14. Allied41 A 5895 or equiv.)

13-Induction pickup coil wound with No. 34enameled wire (see text)

MOTOR -1 rpm motor, 117 VAC (Olson MO -113)NL1,NL2-NE-2 neon lampPL1-11-pin chassis connector (Amphenol

86-CP1I.)P12 -5 -pin plug (Amphenol 7I -5S)PL3,PL4,PL5--Subminiature phone plug

(Lafayette 99 C 6210 or equiv.)POWER SUPPLY -9 V power supply (Lafayette 99

C 9021)Q1,Q2-2N217 transistor

RECORDERS 1, 2-Battery-operated transistortape recorder (see text)

R1-47,000 ohm, 1/2 watt, 10% resistorR2-33,000 ohm, 1/2 watt, 10% resistorR3,R4-100,000 ohm, 1/2 watt, 10% resistorRY1-SPDT relay, 5,000 -ohm coil (Lafayette 99

C 6091 or equiv.)SI-S4-SPDT microswitch, leaf actuator (ACRO

2CMD1-2AXX-A24. Allied 56 A 5030)S5-SPST toggle switchS6-Normally-open miniature pushbutton switch

(Lafayette 99 C 6159 or equiv.)S7A,B,C-3-pole, 4 -position non -shorting rotary

switch (Mallory 3234J)S01 -11 -pin cable socket (Amphenol 78-PF11)S02 -5 -pin miniature socket (Amphenol 78-S5S)SPKR 1, 2 -8 -ohm, 2 -in, speaker (Olson S-636 or

equiv.)SR1-SR3-Silicon rectifier, 750 ma, 400 PIV

(Lafayette 19 C 5001 or equiv.)Tl-Filament transformer: 2.5 V @ 1.5 A (Allied

54 A 3712)TONE OSCILLATOR-Miniature code oscillator

module (Lafayette 19 C 1513)Misc.-'%-in. dia. x '4 -in. long shaft coupling

(Allied 47 A 1108 or equiv.), 7 x 9 x 2 -in.aluminum chassis, 9 -conductor cable (Belden8449 or equiv.), penlite-cell holder, wheelcollars.

the back of the arm down, and pulls theflattened end upward to "answer" the phone.At the same time, the back of the arm pressesS6, which latches RY1 to keep the timingmotor running. Make sure S6 is pressedfirmly. If the timing motor isn't kept running,L2 will stay pulled in, keeping the phone offthe hook indefinitely!

Handset -earpiece coil L3 is cemented tothe top of the cabinet right under the ear-piece. Terminate the shielded wires from L3and both speakers (unshielded) with minia-ture phone plugs near the mating recorderjacks. The shielded wires from LI and un-shielded wires from speaker I go to the chas-sis binding posts.

Power Cable Harness. The tape recorderssuited to the TAS use 1.5-V batteries to op-erate the motor and 9-V for the amplifier.In the TAS, four separate shielded cablesterminate in a 5 -pin plug (PL2) at one endand home-brew connectors at the other end.The schematic of the harness is shown atthe bottom of Fig. 4.

Especially important is the use of diode\D2 and D3 and their proper installation.

Shielded wire (thin mike cable) is necessaryto prevent excessive motor noise pickup fromthe amplifier power leads. For the 1.5-V bat-tery terminations, cut a I% -in. piece of I -in.dia. wood dowel and push thumbtacks intothe ends for contacts. Solder the wire ends tothe thumbtacks. The dowel assembly shouldhe installed in place of a C -cell. Wrap thedowels with tape and label them recorder I orrecorder 2. If your recorders use two C -cells,make two more dummy batteries from thedowel to take up the space and to maintainthe contact pressure.

Parts Substitutions. While the TAS lendsitself to modification, take it slowly. Themotor, solenoid and microswitches specifiedwork well together in this application. Any1 -rpm motor might be substituted, but youmay encounter mounting and shaft -couplingproblems. The specified microswitches re-quire very little operating force so they don'tcause the cams and motor to stall.

Final Assembly. Insert plug PL2 into chas-sis socket S02. Slide the chassis into the backof the cabinet, placing the recorder I C -cellblock and one of the 9-V connectors on the

bottom shelf. Push cable plug PL I into cabi-net socket SO1. Connect the shielded wirefrom pickup coil LI to insulated bindingposts BPI and BP2 on the back of the chassis,and connect the wires from speaker 1 toBP3 and BP4.

Load the recorders with tape and put theirfunction switches in the stop position. In-stall the dummy batteries and attach the 9-Vconnectors (made from the connectors ofdead 9-V batteries) to each recorder. Slidethe recorders onto the shelves in the cabinet,folding the power cables under each recorderso they won't interfere with reel rotation.The miniature plug from the monitor speakergoes into the headphone jack of recorder 2.Headset earpiece ( recording) col L3 plugsinto the mike jack of recorder 2.

Preliminary Checkout. Make sure switchS5 is of, and that function switch S7 is innormal -operation position. Both recordersshould be set at stop. Plug in the line cord-nothing.should happen. Now turn on S5-the red pilot light (NL2) should come on. Ifcan I is not in the neutral position, L2 willactuate the rocker arm and the timer motorwill run. Let it complete the sequence, atwhich time L2 will release the rocker armand the timer will stop. Now, put functionswitch S7 in the recorder 1 position. RecorderI should now operate completely indepen-dently of all the other parts of the TAS. Youshould be able to record, rewind and play-back by using the recorder controls in aconventional manner. Try this to be sureyour power harness is wired properly. Nowput S7 in the recorder 2 position. This willallow recorder 2 to operate independently asjust described for recorder 1. Try out eachrecorder for recording, rewinding and play-ing to verify proper power harness wiring.

Now, turn off S5. Put S7 in the test/re-cycle position. Position the controls of re-corder I for playback and of recorder 2 forrecording, with -volumes set at low levels.

'Now turn S5 on. The timing motor shouldt!" run continuously and all sequencing should

take place except the operation cf L2. Slightreadjustment of the cam positions will cor-rect sequencing problems. Make sure the camsetscrews are tight so the cams don't rotateon the shaft.

Final Checks. Make the master answeringtape on recorder 1 by placing function switchS7 in the test/ recycle position and plugginga microphone into recorder l's microphonejack. Set recorder l's control to record. Keep

the volume low enough to avoid acousticfeedback from answering speaker. Wait acouple of seconds after recorder 1 starts andtime your answering message to end a fewseconds before recorder 1 stops. The mes-sage used at the beginning of this article istypical of one you might want to use. Nowwait until the sequence has come aroundagain, and when recorder 1 starts, repeat theanswering message. Using 600 ft. of tape on3 -in. reel, you can get almost 30 answers ona tape. Recorder 2 will have enough tape torecord about 15 messages. After the 15thanswering message, your message should tellthe caller to try again in a few hours, sinceyou cannot record the message after the 15thcall without resetting the unit.

Near the end of the final message, turnS7 to the normal -operation position. Thiswill shut off the timing motor at end of thecycle. Remove the microphone from re-corder I and get ready to accept incomingcalls. With S7 in the recorder I position, putrecorder 1 in the playback mode and rewindthe tape to the beginning. Use a long whiteleader on the tape to give you a definitestarting point and to avoid unreeling the tapeby rewinding too far. Set switch S7 to re-corder 2 and rewind recorder 2's tape to thebeginning, then set it up for recording.

Put S7 in the normal -operation positionand shut off S5. This is to prevent S6 frombeing pressed and running the timer as youraise the enable/disable arm to position thephone. Remove the telephone handset andplace the phone base so that the spring -loaded arm holds down the phone pushbut-ton. Place the handset on the wooden cradle,with the mouthpiece over the speaker andthe earpiece over L3.

The telephone may be used normally bypushing it slightly backward to release thepushbutton. Call a friend and ask him tocall you back. Reposition the phone baseunder the arm, put the handset back on thecradle, turn on switch S5 and wait. The phoneshould ring about three times before solenoidL2 pulls in, lifts the arm and . .. well, by nowyou should be familiar with what happens.Adjust playback and record volumes (you'llbe able to hear the caller through the monitorspeaker as the recording is being made).

Make certain the phone is really hung upor callers will just get a busy signal. Tightenor shorten the spring and position the phonebase under the arm to insure full pressure onthe pushbutton -6-

61

..111111b.--11=IP

Vest -PocketModulation Scope

gnuVal* - Y +

See what your signal looks like and you can have the best on the air!

By HERB FRIEDMAN, KB19457

CITIZENS BAN DERS are constantlybeing drowned in a sea of modulation

theory. As a result, they overlook the onereally important but simple rule: modulationshould reach 100 per cent as much of the timeas possible. Less than 100 per cent meansfeeble talk power. Over 100 per cent meansdistortion and sideband splatter (and perhapsa nice note from old Fox Charlie Charlie).

So they go ahead and try speech clippers,compressors, limiters and other modulationboosters. What happens? They still end upwith poor reception reports.

Clippers and compressors boost only theaverage voice power. It is the peak power youhave to watch out for-it causes overmodula-tion.

The only way to he sure you're putting outa potent signal is to put the signal on display.Unfortunately, peak -indicating modulationmeters cost hundreds of dollars and aremanufactured mainly for commercial appli-cations.

How, then, can you accurately and at aglance tell just how good your modulationis? By using our Vest -Pocket ModulationScope, of course. It's a peak -indicatingmodulation instrument which can be built forwell under $50-under $25 if you pick up asurplus I EP1 cathode-ray tube (CRT).

With the scope connected to your rig,youcan see instantly what your modulation per-centage is. Over 100 per cent and you canexpect your signal to he distorted. ( Actually,100 per cent negative modulation causestrouble. A transmitter which reaches 200 percent positive modulation but less than 100per cent negative modulation does not causedistortion or sideband splatter.)

Our scope is designed specifically for CBmodulation measurements. A special RFinput transformer amplifies the low RF volt-age going to the antenna to about 100 V butdoes not increase the SWR or cause a loss inRF output. A capacitive voltage divideracross the transformer permits adjustment forI to 3 watts of transceiver output power. Asingle component change permits operationwith transceivers whose output is in excessof 3 watts (to a maximum of 4 watts).

The scope will provide either a trapezoidor a modulation -waveform ( MW) display.All tube transceivers have a relatively highmodulation voltage-approximately 200 V,which will be adequate to drive the IEP1'shorizontal plates for the trapezoid pattern.In solid-state rigs, however, the voltage isn'tsufficient to produce a trapezoid pattern.Therefore, if you have a solid-state rig use theMW connections. An advantage to the MW-

ty)

Fig. 1-Space is at a premium in 5 x 7 x 2 -in. chassis so mount parts exactly where shown. Weused a special socket on VI; however, you may solder wires and components to tube's pins.

lisplay setup is that an internal modificationn the transceiver is not required.

As the scope has no effect on the RF out-put, it can be left permanently connected tothe transceiver so that the modulation canbe monitored at all times.

Construction: All part values are criticaland no substitutions can be made. Becausethe layout also is important, the pictorial andphotographs should be followed as closely aspossible. Our scope was built in a 5x7x2-in.aluminum chassis.

Cut all holes before mounting any com-ponents. Note the cabinet's internal cornerflanges. Locate the opening for the CRT onthe 5 x 2 -in. side so the hole just clears theflange-don't cut into the flange.

Cut the opening for the CRT with a 11/2 -in.chassis punch or a hole saw. Take up theslight extra clearance between the CRT andthe cabinet by wrapping two turns of tapearound the front edge of the CRT. Positionfocus control R3 and intensity control R8between the CRT and the edge of the cabinet,

but take care that the hole for R3 does notbreak off the corner flange.

We specify SO -239 connectors for SOIand S02. However, you may use a differenttype to match those you now have. Cut theholes for LI and C3 at least 11/s in. below aline between the centers of SOI and S02..Trimmer capacitor C3 requires a hole slightlylarger than 1/2 in. First drill a 1/2 -in. hole andthen enlarge it with a round file.

Coil LI must be wound carefully or therewill be a loss in antenna efficiency. If LI iswound sloppily, take it apart and start allover again. Refer to the sketch of the coil inFig. 3. Wind the secondary first. Tensilize a2 -ft. length of #26 enameled wire by clamp-ing one end in vise and pulling on the otherend until the wire goes dead slack. (If thewire isn't tensilized the coil will unwind.)Scrape approximately 1/4 in. of insulationfrom one end of the wire and solder it to lug4. Run the wire along the form for Vi in.and then wind 8 closewound turns. Solderthe other end of the wire to lug 3.

63

Solder the end of a 2 -ft. piece of tensilized#22 enameled wire to lug 1 and run the wirealong the form to the beginning of the firstcoil. Wind 2 turns as shown and connect thewire to lug 2. The completed coil consists ofthe 2 -turn primary slightly overlapping the8 -turn secondary.

Solder a jumper between the lugs I and 4and extend this jumper about I in. past thesecondary's start lug (4). Connect 10-p.p.f

INTENSITY

Fig. 2-We did not in-stall connector S03 inour model for trapezoiddisplay. If you wish to,move LI and C3 (seeFig. 1) toward SO1 andS02. install S03 belowLI. Shaft on potentio-meter R6 (directly underVI's mounting bracket)should be cut short soit doesn't protrude be-yond side of cabinet.

disc capacitor C 1 across secondary lugs 3 and4. Cut one lead of C2 to 3/4 in. and connectit to lug 3.

Attach a 3 -in. insulated lead to lug 2. Thislead will be cut to the correct length whenLI is connected to the wire joining SO1 andS02.

The CRT is held in place by a strap madeof 1/2 -in. -wide scrap aluminum. Simply wrapthe strip around a broom handle to form a

RED / YELN. C.

RED

C>2

YI

GRN

Fig. 3 -For trape-zoid display, breaklead going from SRI,SR2 to C8. Then con-nect C8 to connectorS03. For clarity incoil diagram below,primary winding (P)is shown centeredover secondarywinding (S). Itshould be woundover secondary atbeginning of wind-ings near lugs 1, 4.

clamp shape. But be careful. If the clamptoo tight it may crack VI. A single mountingscrew is all that's needed to hold the clamp.

RF FINAL

MODULATOR B+

0

.05,0

TOANT

SO4_b-,

Fig. 4-Add components shown in color to trans-ceiver for trapezoid display. To locate point Xin your transceiver, refer to the set's schematic.

Fig. 5-Patternshown represents=modulated carrier.The height of thepattern will doublewhen the 100 percent modulationlevel is reached.

Fig. 6- Nearest pat-terns are called modu-lation waveforms. Pat-terns in far column are

/11% referred to as trapezoiddisplays. To displaytrapezoid pattern (notpossible on solid-statetransceivers), you mustmodify transceiver asshown in Fig. 4 to feedpart of audio modulat-ing signal to the scope.

A 3/s -in. spacer or stack of washers betweenthe clamp and the chassis will center theCRT. (Do not install the CRT yet)

Horizontal -gain control R6 is mounted ona U -shape potentiometer mounting bracketinside the chassis. Temporarily install R6and mark the shaft where it lines up with theedge of the chassis. Cut the shaft at the markand then hacksaw a slot into it for a screw-driver.

To avoid a parts jam, install the compo-nents in the following order: connectors SO1,SO2 (and S03, positioned halfway down therear panel, if a trapezoid display is desired).The line cord and T1. Next, R3, R6, R8 andall terminal strips. Install the SOI-S02jumper, LI then C3. Complete all wiring as-sociated with these components. Install allremaining components with SR1-SR4 last.

Install R2, R7 and the jumpers betweenpins 8, 7 and 10 on VI directly on VI's pins.Install VI. To be sure of getting a horizontaltrace, turn VI so that pin 1 is aimed towardT1. Complete all wiring to VI's pins andleave sufficient slack in the wires so VI canbe turned for a horizontal trace.

Checkout. Connect the positive lead of aVOM set to indicate at least 400 V (DC)to the jdnction of SR1 and SR2. Connect the

PARTS LISTCapacitors: 400 V or higher unless otherwise

indicatedC1,C2-10 AAf ceramic discC3-7-35 AO trimmer capacitor (Centralab

827-13, Allied 43 A 1519 or equiv.)C4,C5,C8,C10-.01 Af tubular or ceramic discC6-.1 Af, 75 V ceramic discC7-.005 µf ceramic discC9-.5 Af, tubularC11-.05 Af, ceramic disc11-Coil wound on J. W. Miller 42A000CB1

coil form (Allied 54 D 3913. $1.56 pluspostage. Not listed in catalog)

Resistors: 1/2 watt, 10% unless otherwiseindicated

R1-1 megohmR2,R7-1.2 megohmsR3-250,000 ohm, linear -taper potentiometerR4-150,000 ohmsR5-470,000 ohmsR6-1 megohm, linear -taper potentiometerR8-50,000 ohm, linear -taper potentiometer

with SPST switchS1-SPST switch on R8SO1,S02,S03,SO4-S0-239 coax connector

(see text)SR1-SR4-Silicon rectifier: 750 ma, 400 PIV

(Allied 24 A 9693)Tl-Power transformer; secondaries: 250 V @

25 ma, 6.3 V @ 1 A. (Allied 54 A 2008)V1-1EP1 cathode ray tube (RCA. Allied 1EP1-

Dept. 5901. $25.75 plus postage. Not listedin catalog)

Misc.-5 x 7 x 2 -in. aluminum chassis. 5 x 7 -in. aluminum chassis -bottom plate, terminalstrips, AC line cord

65

meter's negative lead to the chassis. Set R3.R6 and R8 full clockwise and turn on power.If the meter doesn't rise to over 350 V im-mediately pull the plug quickly and checkthe power supply for a wiring error.

If all is okay, a horizontal trace will appearon the CRT after a short wait. The tracewill be centered. Turning R6 counterclock-wise will cause the trace to shrink to a smalldot in the center of the screen. The correctsetting for R6 is that which makes the tracejust touch the edges of the CRT. Focus thetrace with R3.

Connect the transceiver output to SO1 andthe antenna or a dummy load to SO2. Wesuggest that an SWR meter be connected be-tween SO2 and the load.

When you transmit, the trace should ex-pand. Using an alignment screwdriver, adjustLI's slug for maximum pattern height. Thisshould correspond to lowest SWR and maxi-mum output power. Now adjust C3 so thepattern is about 1/2 in. high. If high transmit-ter output prevents the pattern from beingreduced to 1/2 in.. change C2 to 5 µill

Talking into the microphone will cause theCRT to display the waveforms shown forMW in Fig. 6. Note that at 100 per cent mod-ulation, the negative valleys just reach thebaseline (appearing as a bright dot) while tht.positive peaks (peak -to -peak) are exactlytwice the height of the unmodulated carrier.When the modulation exceeds 100 per centthe peak -to -peak height will be more thantwice the unmodulated carrier height andthere will be a distinct break at the baseline.The break is caused by more than 100 percent negative modulation.

If you prefer the trapezoid pattern, theCRT will display them as shown in Fig. 6under trapezoid. Note that with no carrierand no modulation there is no horizontal line.While modulating, adjust R6 so the horizontalsweep occupies about 34 the total width ofthe CRT. Note that at 100 per cent modula-

tN

Fig. 7-Adjust LI byfeeding the transmitteroutput through thescope to a load. Thenadjust Lt's slug formaximum output power,lowest SWR or maxi-mum display height.Instrument here is SecoElectronics Model 510CB -transmitter tester.

tion, the pattern forms a point at the base-line (equivalent to the dot in the MW pat-tern). When 100 per cent negative modula-tion is exceeded the trapezoid grows a tail-a bright line. The greater the over -modula-tion the longer the tail.

The Trapezoid Modification. To obtain thetrapezoid pattern make the following modi-fication after the Scope has been checked outfor the MW pattern. Install SO3 on the rearof the cabinet. Disconnect C8 from SRI -

SR2 and connect C8 to S03.Install a connector (SO4) on the rear of

your transceiver and connect the center con-ductor of SO4 to the modulated B+ feed pointin your transceiver's RF final stage. A typicalinstallation is shown in Fig. 4. Point X is theB+ feed point. Regardless of the exactcircuit used in your transceiver. the mod-ulated B+ feed is from between the modula-tion transformer and the RF final's plateinput. While capacitor C11 is not needed ( asthere's a DC blocking capacitor at the inputof the Scope) it is recommended as a safetyfeature to keep the high DC voltage offSO4. Connect SO4 to SO3 with coax.

Fig. 8-To determine where to put modulationreference lines, refer to Fig. 5. Then scribe thelines on face of the CRT with a grease pencil.

S:-TO BETTER TAPES

By REID ETTA THERE she sits in a sealedcarton. You tear away the

cover, toss the instruction manual to one side,fight ten minutes to work your way througha mounatin of plastic foam. Finally-yourspanking -new tape recorder!

Quickly now, and she's on the table. Oglesfrom adults and shrieks from children. Andsuddenly it hits you. The only thing sittingon top of the machine is an empty take-upreel (if you were lucky enough to get onewith the recorder). And, unfortunately, noone yet has figured out how to record on thinair.

In order to capture those golden soundsforever, you obviously will need recordingtape. But what kind? There are more varieties

-1# and prices of tape on the market than fliesin a fruit market. Basically, however, we canreduce everything to two types: name -brandtape and white -box tape (which usually sells

411 for several bucks less than the name -brandstuff). Since you know at least three tapebuffs who swear by white -box tape, you nat-urally will be inclined to join the save -a -buckbrigade. But will you really save? Or will youfoul your recording heads and capstan, sufferthrough dropouts during your favorite sym-phony and make a mess out of a routine edit-ing job?

Assuming reasonably good electronics( which most recorders have), the tape itself

determines the final results of your recordingefforts. And for recordings of highest fidelitythe tape must be free from surface irregulari-ties, which can cause signal drop -out. It mustbe free of oxide clumps, which cause exces-sive head wear (with resultant loss of high -frequency response). It must have oxidebound tightly to the base to avoid excessflake -off to foul the heads and capstan, result-ing in uneven drive speed and microscopictape lift-off from the heads. It must displaypractically no variation in recorded levelfrom beginning to end of a reel so sectionscan be spliced together without noticeablechanges in playback level. And it must havefrequency and distortion characteristicswhich enable your recorder to deliver on itsmaximum capabilities.

Sound like tough specifications? They are.And while you could start with white -boxtape, as a general rule it simply isn't suitedto quality music recordings. White -box tape,among other things, can be cut -down new orused computer tape; second -quality tape, i.e.,tape which plain couldn't meet manufac-turer's standards; or it even might be usedtape. Or it could be cheaply -made tape withpoor oxide adhesive and a surface like sand-paper. All things considered, tape by reputa-ble manufacturers-Audio Devices, Kodak,3-M, RCA and others-always is to be pre-ferred for serious recording.

n7

1 Steps to better tapes

Then there's the question of the materialitself. Total recording time depends on thesize of the reel and the thickness of the tape.Standard tape, such as Scotch 111, is 1.5 -milacetate. This means the base is made of ace-tate and the base plus oxide coating is 11/2thousandths (.0015) of an inch thick.Though such tape is suitable for average use,acetate deteriorates with age-and if perma-nence is important the somewhat more ex-pensive heat- and humidity -resistant Mylar-base tape is a wiser choice.

When a standard reel offers insufficient re-cording time extended-play tape should beconsidered. For use of a thinner base meansmore tape can be wound on a given size reel.Extended-play tape can be purchased in boththe +50% and +100% sizes, though the+100% tape is extremely thin and compara-tively easily stretched or broken.

Having selected your tape, you slap a reelon the machine and away you go. The tapeinventory builds and builds: Aunt Mini sing-ing at sister's birthday party (not to mention

Uncle Harold's tired sweet -sixteen jokes). 50mi. of music off the tuner, three weeks' sal-ary in prerecorded tapes. And then it hap-pens. First the tapes seem to have a funnyhiss. Later, the hiss grows louder and is any-thing but funny, no matter how defined. Headmagnetization has struck again.

Except on those machines with built-in de-magnetization, sharp -impulse overloads can(and do) magnetize the recording head, justas contact with a magnetized tool can mag-netize a record or playback head. When tapepasses over a magnetized head a hiss is super-imposed, much as though you passed the tapeover a weak magnet. Another symptom ofa magnetized head is partial erasure of pre-recorded high frequencies (this is what takesthe sparkle out of prerecorded commercialtapes).

To avoid the magnetization problem, sim-ply use a head demagnetizer, such as the Rob-bins HD -6, at periodic intervals-say once aweek if the recorder gets moderate service.It takes just a second or so to hold a demag-netizer against a head but those few secondscan mean the difference between noise -fulland noise -free listening.

Okay, you now are all set for the best inrecording-or are you? If yours is a profes-sional or semi -pro machine, there's goodchance you didn't get a microphone. Thenagain, even if you did get a mike, chances

are your live recordings have nownere nearthe fidelity you get from a tuner or fromprerecorded tape. Microphones supplied withmost recorders often are just fancy -cased ver-sions of the cheapie models that come withbudget recorders. And all leave a lot to be de-sired in the way of fidelity and convenience.

Quality recordings require quality micro-phones but you don't have necessarily to gofor broke. Good mikes start at about $30.going up the ladder to $150 for broadcast

68

quality. If you want to keep costs down, byall means consider the Electro-Voice 636 andthe Shure 550S. Both exhibit a notablysmooth quality that enhances the sound frombudget recorders. A little better quality formedium -price recorders can be found in theAKG line, the Norelco D1 19ES, the Shure556S and the Electro-Voice 676. And if youwant your tapes to sound like a good -musicstation try a broadcast mike such as the Elec-tro-Voice 666.

While you're concentrating on putting thehighest of fi on tape, don't overlook dynamicrange-the variations in speech and musiclevels. Sure, recorders are equipped withsome sort of volume indicator: a flashinglamp or magic eye or a VU mete:. But suchdevices give an accurate indication of re-corded level only when feeding from onefound source. They tell you next to nothingwhen you're trying to blend such sources astuner or phono with a mike or several mikes.

For optimum sound balance ut's best tomonitor while recording. Matter of fact, it'sthe only way to obtain precise balance. Andwhile nearly all recorders provide for moni-toring when recording from a tuner, phonoor another tape recorder, silence descendswhen you use mikes (unless you're in themood for the squeals of acoustic feedback).So your next step is to monitoring head-phones.

Inexpensive headphones, such as used forexperimenter projects or ham radio, usuallyare unsuitable since their high distortion andpoor low -frequency response do not give anaccurate representation of what's being fedinto the recorder. Just as you would use hi-fiphones, such as those made by Koss, Norelcoand Telex (among others), with your ampli-fier, so you must use hi-fi phones with yourrecorder.

Thing to avoid is the impedance pitfall

since this can have dire effects on any record-ing. Usually a recorder's headphone jack isin the speaker circuit and any of the low -impedance phones can be used. But it's justpossible that your recorder's headphone jackis in a high -impedance circuit and that theloading caused by low -impedance phones,therefore, would alter the recorder's fre-quency response. When high -impedancephones are called for, use the crystal type,such as the Clevite-Brush BA -200B, whichhave a 90,000 -ohm impedance. (If you're indoubt whether to use low- or high -impedancephones, best check with your dealer or manu-facturer.)

Speaking of several sound sources, the av-erage recorder, even if it sports both high -and low-level inputs, has but one volume con-trol and only one sound source can be con-trolled at a given time. While some of thehigher -price recorders have so-called mixingcontrols, usually only the mike and a high-level input, such as a tuner, can be mixed.

Yet best recordings of musical groups aremade when several mikes are used to balanceindividual instruments or sections. While yousometimes can connect several mikes in par-allel you still have only one volume control.For multiple mike setups or even for multiplehigh-level sound sources (tape recorder andamplified turntable, for example), a mixer-a device that accommodates several soundsources each with its own volume control-is required.

Two types are available to the hobbyist.The first is the passive mixer, such as Lafay-ette's audio mixer, which is nothing morethan a small metal cabinet with two inputjacks, two volume controls and an outputplug to match the recorder's input jack. The

,(1

7 Steps to better tapes

passive mixer will mix any two high -imped-ance sources into a single high -impedanceinput with individual control of each source.Most passive mixers have a slight loss in gain,however (generally on the order of 6 to 9db),and the Lafayette is no exception.

More flexible mixing can be obtained withan amplified mixer, which accommodates upto four inputs, either high- or low-level. Atube model such as the Bogen MX -6A pro-vides nearly 60db mike gain. This means thateven if you're mixing mikes, the mixer outputcan be connected to the recorder's high-levelinput, bypassing the noise of the recorder'smike preamplifier. If you want to save abuck there are the small transistor mixers(such as Lafayette's 99 R 4535) which mixfour mike inputs and provide a small overallgain.

And while you're mixing the sounds of thatmusical aggregation, you may wish to con-sider what best to do with the mike(s). Mostrecorder mikes, if supplied with a stand atall, have an inexpensive metal arrangementthat just about keeps the mike from fallingover when placed on a table. And the tablestands supplied for some of the more costlymikes are no better. To record a musical oreven a dramatic performer it often is neces-sary to prop a stack of books on a chair, stickthe mike(s) on top of the tower and thentrust someone doesn't upset the applecart byknocking down your house of cards.

A better approach is a portable floor stand

like the pros use, a good example being theAtlas CS -33 Take -Apart Floor Stand. TheCS -33 has removable legs which form a rigidtriangular brace, yet it folds up small enoughto be hidden away in a closet. When open,the three legs cover a wide base so, thoughlight in weight, you can stick your best mikeon it without fear of it being knocked over.

Though taping now should be as easy aslistening there still is one giant step that canlead to the best in tape recording. That step-like the six that preceded it-is a step up,of course, this time to a microphone match-ing transformer.

Nearly all home recorders use high -imped-ance mikes and high -impedance mike inputs.While this arrangement is perfectly suitablefor mike cable lengths up to 25 ft., beyondthat the internal capacity of shielded mikecable attenuates the high frequencies. Fur-ther, the high -impedance cable itself is sen-sitive to hum pickup.

When long mike leads are needed, as theyare when recording a high-school band or sim-ilar ensemble, it's best to use a low -impedancemicrophone rated at 50, 150 or 250 ohms.Impedances of this order permit cable lengthsup to several hundred feet. Further, when theline finally reaches the recorder's high -im-pedance input all that's needed is a trans-former, such as the Electro-Voice 502A, tomatch the low -impedance line to the high -

impedance input.Conversely, the matching transformer can

be used to convert a high -impedance mike toa low -impedance output. One also is neededwhen you choose to use a low -impedancebroadcast -type mike with your high -imped-ance recorder. -$

70

Char -Analyst for BatteriesBanish your battery budget forever (well, almost) with our super-duper

do -all and end-all tester/charger (phew!). BY BERT MANN

BATTERIES by the carload! That's al-most the way you have to buy them

these days to keep everything from junior'stoys to dad's heavy-duty flashlight runningall the time

Before you discard those apparently -deadbatteries, however, connect them to the Char -Analyst. In quick time it will check themunder load and show you the true condition.If the battery is on its last legs, merely shift apair of leads, flip a switch or two and theAnalyst will charge the battery, making italmost as good as nem

Often a battery no longer may be able topower a particular piece of equipment; how-ever, it usually is capable of giving severalmore months of service in other gear whichpulls less current

For example, an old C cell required to sup-ply 200 ma to a walkie-talkie might be toopooped to push the signal 10 ft. down theblock. Recharge that battery and put it in atransistor mike mixer that pulls about 10 maand months later the same battery will begoing strong

Reason for this is that as the battery agesits internal resistance increases. When thebattery is connected to a load that pulls a lotof current the high internal resistance causesthe terminal voltage to drop.

When terminal voltage falls to the cutoffvalue-the voltage below which the equip-ment will not operate-the battery is said tobe dead. But in a device that draws littlecurrent it will take much longer for the ter-minal voltage to drop to cutoff value. The

7!

Fig. 1-Because of theangle at which the frontpanel slants back, itwill be more conveni-ent to install the me-ters, controls and bind-ing posts on the panelbefore bolting paneland chassis together.When wiring to the ter-minal strip at the rightof T1 make sure youdon't make any connec-tions to the ground lugsince the circuit mustbe isolated electricallyfrom the metal cabinet.

Char -Analyst for BatteriesPARTS UST

BP1-BP4-5-way binding postC1-100 Af, 50 V electrolytic capacitorM1-0-3 ma DC milliammeter (500 ohms).

Shurite Type 950 (Lafayette 38 C 6083).M2-0-1 ma DC milliammeter. Shurite Type

950 (Lafayette 38 C 6081)Q1-40 watt PNP power transistor (Lafayette

19 R 1503)R1-2,000 ohm, linear taper potentiometer

with SPST switchR2-2,000 ohm, linear taper potentiometerR3-56 ohm, 1/2 watt, 10% resistorR4-10 ohm, 1/2 watt, 10% resistorR5-5 ohm, 5 watt wirewound resistorR6-1 ohm, 5 watt wirewound resistorR7-2,000 ohm, 1/2 watt, 5% resistorR8-13,000 ohm. 1/2 watt, 5% resistorR9-1,500 ohm, 1/2 watt, 10% resistorS1-SPST switch on RIS2-DPDT toggle or slide switchS3, S4-1 pole, 5 position rotary switch

(Mallory 3215) or equiv.)SR1-Silicon rectifier; minimum ratings: 500

ma, 100 PlyTl-Filament transformer; secondary: 24 V

1 A (Lafayette 99 C 6266 or equiv.)Misc.-Power transistor (TO -36 size) mount-

ing kit (Lafayette 19 C 1532 or equiv.),4 x 6V. x 1 -in. open-end aluminum chassis(Premier ACH-1360), 8 x 8 x 8 -in. sloping -

panel cabinet (Premier SFC-500).

Analyst's test section shows you a battery'strue terminal voltage by simulating loads thatpull up to 11/2 A.

The Analyst tests and charges AA, AAA,C and D zinc -carbon, mercury, alkaline andnickel -cadmium cells. Charging current canbe adjusted over a wide range of values.

Fig. 2-Chassis is attached to front panel withmachine screws. Note the 3/16 -in. space betweenthe bottom of chassis and bottom of front panel.

T1

17VAC

BLK

CHARGE CURRENT

CHARGE

BP'

4

CHARGE

r-3 BP::

VOLTAGE

o simplify connections to the batteries,we mounted several different size holders onthe top of the cabinet. If you have a specificneed, say, to charge ten D cells together, theholders can all he for D cells

Construction. Our Analyst is built in an8 x 8 x 8 -in. sloping -panel cabinet. All corn-

® -4- NUTSOLDER LUG

F--ru -41- WASHER

MI CA WASHER

/ CHASSIS

--41- MICA WASH ER

x-01

Fig. 3-Q1 mounting details. Wrap tapearound threaded stud to prevent a short tochassis. Base, emitter leads are not shown.

Fig. 4-T1, SRI, Cl. RIand Q1 constitute powersupply whose output iscontrolled by varyingQ1's bias voltage withRI. When S2 is incharge position (shown).MI is connected in neg-ative buss to measurecharge current. S3 con-nects appropriate shuntresistor (R3 -R6) acrossMl. When S2 is set to"test." R2. MI and se-lected shunt resistor(R3 -R6) are connectedacross battery termi-nals. M2 then indicatesbattery voltage as R2increases test current.

ponents (except those in the power supply.which are mounted on a 4 x 61/a x 1 -in. open-end chassis) are mounted on the cabinet'sfront panel

Note that transistor Q1 is mounted underthe chassis so connections can be made to itsterminals on top of the chassis. The entirecircuit is isolated electrically trom the cabi-net to prevent damage to Q I should a testlead touch the cabinet

As supplied, the transistor mounting kitdoes not include an insulator for Q1'sthreaded mounting stud, which also is thecollector lead. Drill an oversize hole (9/ 16in.) for the threaded stud. Then insulate thestud with a few turns of electrical tape oran insulating sleeve. Make no connectionsto Q1 until you measure the resistance be-tween its base. emitter and collector leadsand the chassis. It you measure any resist-ance at all track down the trouble beforegoing on

The specified meters (substitutes are notpermitted) must have their scales changed.To remove them, gently take off the frontcover by bending back the tabs at eachcorner. Then remove the two screws holding

Char -Analyst for Batteries

the scale and slide the scale out, taking careyou don't bend the pointer.

Using rubber cement, cover the existingmeter scales with the scales in Fig. 5. The3 -ma meter, M I , now has two scales: 0-3and 0-15 ma. This provides 30, 150, 300 and1,500 -ma ranges. The 0-1 ma meter, M2,will have two voltage scales, 2.5 and 15 V.

Mount the chart in Fig. 6 on the side ofthe cabinet. The chart shows test currentsand the 16 -hr. charge currents for manypopular batteries. If you plan to chargenickel -cadmium batteries, use the charge cur-rent specified by the manufacturer.

Testing. Set S2 to test, R2 to full counter-clockwise and S3 and S4 to the appropriatecurrent and voltage ranges. Then connectthe battery to BP3 and BP4 with clip leads.Rotate R2 until M I indicates the exact testcurrent. Batteries that indicate above 1.2V per cell are good. (To determine the num-ber of cells divide the battery voltage by 1.5).An indication less than 0.8 V for each 1.5-Vcell in the battery means the battery is ex-hausted and should be recharged. If the vol-

Fig. 5-Top scale is for M2, bottom is for Ml.

cage is between 1.0 and 1.2 V per cell, thebattery can be pepped up with a charge atabout half the recommended rate (precisecharge rate is determined by experience).

Charging. The recommended charge cur-rent usually is 150 per cent of the energy re-moved, distributed over a 16 -hr. period. Forexample, suppose a D cell was used in a cir-cuit that pulled 300 ma for ten hrs. Thisamounts to 3 ampere -hours (ampere -hours,A -H, = current in amperes x time in hours).To recharge the battery, 150 percent of theexhausted energy of 3 A -H (4.5 A -H) mustbe put back in. At the recommended chargetime of 16 hrs. the charge current (A -H di-vided by time) is 4.5/16 or 0.28A (about300 ma).

To charge, set S2 to charge and connectthe batteries to BP 1 and BP2. Turn R 1 fromthe full counterclockwise position until powerswitch S1 clicks on. Set S3 to the appropriatecharge -current range and adjust R 1 until theexact current is indicated on M I. Keep youreye on the current for the first minute or so toprevent its creeping to too high a value.

Note. Always set S3 to the current rangebefore testing or charging. Since the shuntsaffect the operation of both circuits it is nor-mal for S3 not to decade accurately whenswitching from range to range when testingor charging. For example, if testing at 200ma with S3 set to the 300 -ma range, the testcurrent might shoot up to 500 ma when S3is changed to the 1.5-A position. 1_

TYPICAL TEST AND CHARGE CURRENTS

BatteryVoltage

Test Current(ma)

Charge Currentfor 16 hrs. (ma)

1.5 (AAA) 30 201.5(AA) 50 501.5(C) 50 1501.5(D) 270 150

I.5(D)* 50 1504.5 100 150

43* 50 806.0" 270 150

6.0* 50 509.0* 9 16

13.5 9 16

Transistor adio or electronic -applications type**Lantern or heavy-duty type

Fig. 6-For future reference, attach this chart otypical battery test and charge currents eitheron the front or on the side of the charger's cabinet.

74

gl)

Band -Switched VHFerOur rig tunes hot listening from 26 to 162 mc without annoying coil changing.

BY CHARLES GREEN. W6FFQ

IT started as a sad story-Hans Christian Andersen's tale of the Ugly Duckling. Butit had a happy ending after the swan grew up and found that in his own right he.

too, was a real swinger.So it is with the VHF portion (30-300 mc) of the radio spectrum. Once neglected.

the VHF frequencies now are radio's most wanted. They're loaded with good listening.The line -of -sight characteristic of VHF transmissions has changed from a handicap intoa blessing in disguise. Reason is. it permits constant day -and -night coverage of localareas. This mode of transmission has proven itself to be ideal for commercial andspecial -service broadcasting of many types

With our three -tube VHF receiver, you can listen in on the most active parts of theVHF spectrum. Band A (26-31 mc) covers the Citizens Band and the 10 -meter hamband. Band B (47-54 mc) tunes police and fire departments, as well as the 6 -meterham band. Band C (91-107 mc) covers most of the FM broadcast band. Band D

(114-134 mc) lets you listen to the aircraft band and Band E (137-162 mc) coversthe Civil Air Patrol, the 2 -meter ham band and public -safety vehicles.

Our receiver's circuit uses a frame -grid triode in a reflexed grounded -grid RF stage.This stage feeds a superregen detector followed by a power amplifier stage that drivesan external speaker. The receiver, with its AC power supply, is built on a 7 x 7 x 2 -in.aluminum chassis. Construction is straightforward and the coils are easy to wind.

75

SI POSITIONS

A 26.5 - 31 11C

8 41 - 54C 91 -106.5D 114 -134E 1375 - 162

117

VAC

65

PARTS LISTCapacitors: 1,000 V ceramic disc unless

otherwise. indicatedCl,C7-47 µµfC2,C10,C11,C20,C21,C22-470C3-Gimmick capacitor: three turns of

hookup wire (see text)C4-6.5-13 µµf variable capacitor (Lafayette

32 C 0917)C5,C12,C15-.01 iifC6,C13,C16,C17,C18-.001C8-100 µµfC9-5 At 150 V electrolyticC14-10 µf, 15 V electrolyticC19A,B,C-50/30/20 µf, 150 V electrolyticF1-1/4 A pigtail -lead fuseJ1,J2-Phono jackCoils: No. 16 enameled wire (see text)L1-15 turns, 9/16 -in. I.D., 'A and 1/4 -in. leadsL2-9 turns, %-in. I.D., %-in. leadsL3-3 turns, 3/s -in. I.D. 3/, -in. leadsL4-3 turns, 1/4 -in. I.D., %-in. leadsL5-11/4 turns, 1/4 -in. I.D., 34 -in. leadsL6-24 µh RF choke (J. W. Miller RFC -28.

Lafayette 34 C 8971). Remove 10 turnsfrom each end (see text)

L7-1.72 ith RF choke (.1. W. Miller RFC -144.Lafayette 34 C 8973)

Resistors: 1/2 watt, 10% unless otherwiseindicated

R1-270 ohmsR2,R7-10,000 ohmsR3-=1 megohm audio -taper potentiometer

with SPST switchR4,R5,R10-120,000 ohmsR6-8.2 megohmsR8-50,000 ohm linear -taper potentiometerR9-220,000 ohmsR11-1 megohmR12-470 ohms. 2 wattsR13-1.800 ohms, 2 wattsR14-15,000 ohmsS1A.S1B-2-pole, 5 -position ceramic rotary

switch (Mallory 173C. Lafayette 30 C 4058)S2-SPST switch on R3SRI-Silicon Rectifier, minimum ratings: 200

ma, 400 PIVTl-Power transformer: secondaries: 125 V @

15 ma. 6.3 V @ 0.6 A (Allied 54 A 1410or equiv.)

T2-Output transformer: primary: 10.000ohms: secondary: 4 ohms (Allied 54 A 1448or eauiv.)

V1-6ER5 tubeV2-6CB6A tubeV3-6AK6 tubeMisc.-2 x 7 x 7 -in. aluminum chassis. 7 x 7 -

in chassis bottom plate, 7 -pin tube sockets(3). terminal strips

RIO

DETAIL OF Si

TO GND.LUG

GND.LUG

J2

TO GND. LUG

TO C4, C7 8

TO C3 (GIMMICK)

6ND.LUG

Band -Switched VHFerConstruction

Tape a piece of graph paper over thechassis top and front. Lay out on the paperall chassis holes, scaling your dimensionsfrom our under -chassis photo. Do not spreadout the parts. Keep them in the same placesshown in the pictorials. As in all high -fre-quency circuits, parts placement and wiringare critical-especially around bandswitchSI.

The bracket which supports tuning capaci-tor C4 on top of the chassis is made from apiece of scrap aluminum. The dimensions arenot critical so long as the bottom of C4 isabout 3/16 -in. above the chassis. Our bracketis 11/2 -in. high by 21/4 in. wide; it has a 318 -in.mounting foot.

Position the ground lugs for coils LIthrough L5 on a line between bandswitch SIand V2's socket. Wind the coils on eitherwooden dowels or drills. The number ofturns, inside diameter and lead lengths ofthe coils are detailed in our Parts List. Besure the coil lead lengths are as specified andthe coils are mounted as shown in the dia-

Incoming signal amplified by grounded -grid stage(V1) is fed via C3 and C7 to superregen detectorstage (V2). Audio is fed through low-pass filter(RIO -C13) back to VI. Amplified audio is fed bylow-pass filter (R5 -C6) to audio amplifier V3.

gram under the schematic.The coil -winding information is approxi-

mate. This means the tuning range of eachcoil will vary, depending on the way youwind it ( wind each coil as shown in the detailpictorial of SI under the schematic) and yourwiring layout. Do not crimp the wire leadsof the coils on the bandswitch lugs andground lugs. Just solder them so they can bedetached easily. This will pay off later whenyou are calibrating the dial and wish to ad-just the tuning range of each coil.

Carefully unwind ten turns of wire fromeach end of L6 and solder the remaining wiresto the leads coming out of the ends of theform. This modification is necessary to raisethe self -resonant frequency of the coil at the

Because of operating frequencies it is importantto duplicate our layout. Multiply dimensions inphoto by 3.1 to lay out 7 x 7 -in. chassis. Wiringdetails of SI and coils are under schematic.

SEE DETAILFOR St

CONNECTIONS

77

Band -Switched VHFertop end of the 6 -meter band (above 54 mc).

Fabricate gimmick capacitor C3 by solder-ing a length of hookup wire to pin 5 of VIand another length of wire to the appropriatelug on SI. Run the wires in a straight linetoward each other and twist them togetherthree turns. Cut off the excess and make surethe ends do not touch.

Use spaghetti over the fuse and its leads,as well as on all resistor and capacitor leadsthat cross, to prevent shorts. Position thewiring as shown in the photo and keep com-ponent leads to tube sockets as short as pos-sible. Use a short length of 300 -ohm twinleadto connect J1 to the mounting strip to whichCI is connected

After the chassis wiring is completed. cuta piece of cardboard and fit it on front of thereceiver over the tuning -capacitor's shaft.Mount it on the chassis with small bracketsat each side. Our dial is 31/2 x 5 in. and ismade of heavy bristol board. Make a dialpointer by soldering a length of heavy wireto a small piece of sheet metal. Then bendthe metal around the tuning capacitor'slarge -diameter shaft. Cut another piece ofcardboard and put it over the controls on thefront of the chassis.

Calibration and OperationInstall the chassis bottom plate and the

tubes. Plug in the receiver, turn it on and letit warm up a few minutes. Set volume con-trol R3 full clockwise until you hear the typi-cal superregen hiss. This indicates the de-tector stage is working on at least one band.Check R8's action on other bands selectedby SI.

If you have a signal generator that coversthe receiver's frequencies, connect it to an-tenna jack J I and calibrate the dial lightly inpencil. Then remove the dial and ink in themarkings. or use transfer type to make a pro-fessional -looking dial

If necessary. the coils can be squeezed orcompressed to change frequency coverage.Or you can remove the coils and either addor remove turns to change the range. A grid -dip meter is helpful in setting up each coil'srange

The antenna is not critical; anything froma 6 -ft. length of hookup wire (for strong sta-tions). to an outside TV antenna will work.

Rear view of receiver. V1 is at top, left. V2 isin center. V3 is at right below T2. Ti is at loweleft. Note tuning capacitor's mounting bracket

Some signals (particularly the aircraft andemergency -service bands) are vertically po-larized; an outside 2 -meter ground plane isgood for these bands. Refer to the RadioAmateur's Handbook for construction detailson VHF antennas. Or you can buy a com-mercial antenna

The receiver drives a 3.2- to 8 -ohm ex-ternal speaker. Regen control R8 and the.tuning capacitor should be readjusted eachtime you tune a station until signal is strongest. FM stations must be tuned in on eitherside of the signal to achieve slope detection

How it Works

Antenna signals at J I are amplified by thegrounded -grid reflex circuit of V I and fedby gimmick capacitor C3 to the grid of super-regen detector V2. Coils LI to L5 are tunedby C4 for each band selected by SI A. TheRF chokes, L6 and L7, are switched by SI Bfor the proper feedback for each band

Regen control R8 varies the gain of thedetector stage. The detected audio is fedthrough low-pass filter R10 -C13 back to thegrid of VI. VI also amplifies the audio ane.feeds it via low-pass filter R5 -C6 to the gridto power amplifier V3. The audio output ofV3 is coupled through output transformerT2 to external -speaker jack J:

Power for the circuits is supplied by 1 iSR 1 and the R/C filter comprising resistorsR13. R14 and CI9A. B. C. -II

7s

CB Alignment GeneratorYou can peak both RF and IF circuits with this 3 -transistor instrument.

By HERB FRIEDMAN, KBI9457

IT'S the receiver section of -a CB rig thatmakes the difference between reliable and

undependable communications. You canhave the biggest antenna on the street butif the receiver's RF and IF stages aren'ttuned up perfectly you'll simply be spinningyour wheels.

So far as the transmitter is concerned,even if its output decreases slightly or themodulation percentage drops from, say, 85to 50 the loss will often go unnoticed. But ifthe receiver isn't up to snuff the effect willbe apparent immediately. A loss in inputsensitivity means you won't hear weak sig-nals at all. And a change in IF alignment,caused by aging components, will lead toannoying adjacent -channel interference.

While normal wear and tear and com-ponent aging have only slight effect ontransmitter circuits, receiver alignment canbe altered drastically. All it takes is a simplereceiver alignment job to produce a startlingimprovement in performance.

While most service -grade RF signal gen-erators could be used for alignment, the jobshould be done with a crystal -controlled gen-erator, such as our CB Alignment Generator.

Our generator provides modulated or un-modulated crystal -controlled IF signals of455 kc or any frequency from 1300 to 2000kc. And the generator also supplies an RF(26.96-27.25) signal produced by a third -overtone CB transmit crystal. The output

levels of both the IF and RF oscillators areadjustable-maximum output being about150,000 microvolts.

The output frequencies are user -selected.It is necessary only to plug in the crystalsneeded for your particular receiver. Thegenerator is designed for single- or double -conversion receivers. It should not be usedwith receivers that have frequency -synthe-sizing circuits. Such rigs generally requirespecial test equipment.

Figure 2 is the generator's schematic. Notethat there are three separate circuits. Q1 isthe IF oscillator. When SI is in the highposition, an IF signal will be produced in the1300-to-2000-kc range, depending on thecrystal in S01. Plug a 455-kc crystal in S01,set S1 to low, and the output frequency willbe 455kc.

Transistor Q3 is the RF oscillator. Pluga third -overtone crystal into SO2 and you'llget a signal anywhere in the Citzens Band.

Transistor Q2 is the modulator oscillator.When S2 is open the modulator is disabledand either Q1 or Q3 will produce unmodu-lated IF or RF output signals. When S2 isclosed, battery voltage is applied to themodulator and the RF and IF signals will bemodulated about 25 per cent by a 1-kc signal.

Switch S3 controls power to either the RFor IF oscillators. Simultaneous RF and IFoutputs cannot be obtained.

79

CB Alignment GeneratorConstruction

To insure proper operation, the generatormust be built exactly as shown in the pictorial

and photographs. Use only the componentspecified-make no substitutions

The generator is built on the main sectionof a 7 x 5 x 3 inch Minibox. Start construc-tion by mounting the oscillator -board supportbrackets. Then install all the components or,

PARTS LIST81-6-V battery (Burgess Z4 or equiv.'Capacitors: 10 V or higheC1-50 AO silvered micaC2-15 AO silvered micaC3,C4,C5-.05 Af. ceramic discC6-.25 Af, ceramic discC7-50 Af, 10 V electrolyticC8-25 AO silvered micaC9,C10-.001 tif, ceramic discC11-.5 AO, 600 V temperature compensating

tubular (Centralab Type TCZ. Lafayette 33R 2131 or equiv.

J1,J2-Phono pc)LI-3.46-5.8 mh adjustable RF coil (J.W. Miller

21A473RB1. Lafayette 34 R 8886 or equiv.)L2-RF coil wound on J.W. Miller 4400 form

(Lafayette 34 R 8752 or equiv.) See textQ1-GE-1 transistor (General Electric)Q2 -2N217 transistor (RCA'Q3 -2N274 transistor (RCA,Resistors: 1/2 watt, 10% unless otherwise in-

dicatedR1-330.000 ohmsR2,R9-5,000 ohm linear taper potentiometer

R3-270,000 ohmsR4,R7-10.000 ohmsR5-150 ohms R6-220,000 ohmsR8-560 ohm-,SI,S2-DPDT subminiature toggle switch

(Lafayette 99 R 6162) See teaS3-2 pole, 5 position subminiature rotary

switch. Lafayette 99 R 6164 or equiv.,SOI-Crystal socket for type FT -241 crysta!S02-Crystal socket for type HC -6/U crystalTl-Transistor output transformer; primary

500 ohms, center tapped. Secondary:ohms. (Argonne AR -119. Lafayette 33 R8558

XTAL-1-IF-frequency crystal. Available fromTexas Crystals, 1000 Crystal Drive. FortMyers, Fla. 33901. Prices are postpaid. 45t.kc: Type TC-21, .01%, $1.25. 1001 to 1600kc: Type TC-23, $4.50. 1601 to 2000 kcType TC-23, $3.55. Specify frequency whenordering

XTAL-2-Third-overtone CB transmit crystalMisc.-Perforated board, flea clips, 7 x

3 -in. Miniboi,

Fig. 1-Leads shown as broken lines go from front -panel controls to board's underside. Sockets S01. SO2and switches Si and S2 are mounted above the board. 12,R9S3,R2 and J1 are installed under the boars

SO

G.:

O G e

XTAL 1

L'

XTAL I

01 02,03

sot

3

HIGH

51

C4

TT

OUTPUTLEVEL

C

<=.0

3R2 JI

C:o

Ll

OUTPUTLEVEL

RF

J2

L2

TURNS

TAP AT6TH TURN

Fig. 2-Generator's schematic. Circuit at top, associated with Q1, produces IF signal. Circuitassociated with Q3 at bottom generates RF signal. At left -center is oscillator which produces1-kc signal to modulate RF and IF oscillators. RF-oscillator coil L2 is shown in detail at the right

the front panel as shown in Fig. 3. Thebrackets for the oscillator -board are madefrom a piece of 1 -in. -wide x 4 -in. -long scrapaluminum.

Switches SI and S2 are the subminiaturetype: if you use larger stancard toggleswitches move their mounting holes 1/2 -in.

above the crystal sockets.The circuit has two ground busses-you

must use them. Do not simply connect to

the nearest ground point. For example, notethat the ground lugs on R2 and R9 are notsoldered to their case. They are wired to theground busses on tne board.

Wire the oscillators on a piece of per-forated board approximately 27/8 x

To avoid damage to the board, drill themounting holes for Ll, L2, TI and the fourmounting holes for the support bracketsbefore you install :he board to the cabinet.

Fig. 3-Mount compo-nents on front panel asshown, before installingcircuit board. lacks,pots and rotary switchare on line 11/4 in. upfrom bottom. Crystalsockets and toggleswitches are on line 3in. above bottom. Cir-cuit -board brackets are21/2 in. above bottom.

CB Alignment

GeneratorFig. 4-Underside of circuit board.Note the board's mounting brack-ets at each side. Screws protrud-ing through board at left and rightare slug -adjustment screws of LIand L2. Leads from componentsunder board are wired to tips offlea clips. Wires running out ofcabinet go to battery which ismounted in the cabinet's cover.

A

LI is a stock coil and is used as is. CoilL2 is made by winding #22 enameled wireon a J.W. Miller Type 4400 RF coil form.Take about 2 ft. of the wire, clamp one endin a vise and pull on the other end until thewire goes dead slack (tensilized). Scrape off1/4 -in. of enamel from one end of the wireand solder it to the lug nearest the form'smounting nut. Run the wire along the formfor 3/16 in. and then wind six closewoundturns. Bring the wire out from the form forabout 2 in., fold it back to the form makinga loop, twist the loop together and then windfive more close, tight turns in the same direc-tion as the first six turns. Scrape off about1/4 inch of insulation from the free endof the wire and solder it to the lug at theother end of the form opposite the startinglug.

Scrape the insulation off the loop andsolder the two loop wires together. Then cutoff the excess, leaving a 1/4 inch stub-thisis L2's tap

To avoid damage when soldering, assem-ble the oscillator board in this order: SI toLI and the remainder of QI's circuit (do notconnect Q1's emitter yet). SO2 to L2, C8,then the remainder of Q3's circuit with theexception of R6. Q2's entire circuit, TI'sgreen lead to Q l's emitter and R8 from Q3'semitter to T1 's green lead.

Finally, complete the wiring on the under-side of the oscillator board as shown in Fig.1. Mount the battery in a standard D -cellholder centered at the bottom of the cabinetcover. Make certain it is at the bottom soit doesn't short any of the terminals stickingthrough the board. Connect only B 1 's posi-tive (ground) lead. Do not connect BI'snegative lead to S3. as a meter must be con-

nected in this part of the circuit for finaladjustment.

AdjustmentConnect an 0-10 ma DC milliammeter be-

tween BI's negative lead and S3's wiper-the meter's positive terminal connects to B Iand the meter's negative terminal goes to S3.Adjust Ll's slug -adjustment screw so it

sticks out 413 in. Do not plug a crystal intoSO1. Set S3 to IF and note the meter indi-cation-it should be about 0.8 ma. If youare using a 455-kc crystal. close SI and in-sert the crystal-the meter indication shoulddrop to about 0.5 ma.

If the meter's indication does not fall, theoscillator isn't working. Try adjusting L1 'sslug until the meter indication drops withthe crystal in the socket. When LI is ad-justed for 455 kc. it will also be aligned forcrystals in the 1200- to 2000-kc range. It youplan to use crystals for only 1200- to 2000-kc, the 413 in. slug adjustment should requireno further change

Next, plug a third -overtone CB transmitcrystal (preferably a center -band frequencylike channel 11 ) into SO2 and set S3 to theRF position. Adjust L2's slug -adjustmentscrew until the meter indication rises. Thentry a low -(channel 1) and a high-( channe;23) frequency crystal. Note the meter indi-cation with no crystal in S02, then plug inthe crystal again. If the high- or low -bandcrystal does not cause an increase in themeter indication, readjust L2's slug verbslightly until there is an increase in meterindication regardless of the frequency of thecrystal in SO2

Finally, with crystals plugged in. closemodulation -switch S2. The meter indication.

'ft

fY

Note that the installed oscillators are In three distinct groups: RF oscillator on left. IF on right.and modulator oscillator in center foreground. Below. drilling template for cabinet controls (front view).

1.-JI

t We31

1-3/1.

TOP

'BOTTOM

with S3 in either the IF or RF position,should increase by 3 to 5 ma. If it fails toincrease there is a wiring error in Q2's circuit.

Using The GeneratorConnection between the generator and the

equipment being serviced should be madewith coax cable such as RG58/ U. To alignan IF amplifier use a modulated signal andalign the receiver for maximum audio output( in this case you must reduce the generator'soutput to the minimum usable value to pre-vent. the receiver's AVC frcm masking

1 3/3.-P.

2 7/e

77-OSCILLATOR- IMMO IIIIACICETt

3 1/2

1,13 J22-3A'

alignment changes). Or, use an unmodulatedsignal and adjust for maximum receiver AVCvoltage

Similarly, for RF alignment, align eitherfor maximum audio output from the re-ceiver or maximum AVC voltage. Manylower -cost receivers can be aligned to acenter channel such as channel 11 or 12.Some receivers will require two -point align-ment on channels I and 23, while some re-ceivers must he aligned to channel 1, 11 and23. In every case, always follow the alien-ment instructions supplied with the rig.

___y...4__7____., __J__I-.J-1 =-1 -_;,..J.=-J=========-_-4--I -1--,----I -I -4-/--//2' 1

,41------ '

all MillIt's invisible, solves space & weather problems and tunes all bands!

By LEN BUCKWALTER, THOUGH safeKBA4480 from the ravages ofsummer heat, winter winds, driving rain orpelting hail, this swinging skyhook managesto bring in the most -distant short-wave sta-tions. The attic location also means that ourmulti -bander is hidden from the suspiciouseyes of neighbors who think a receiving an-tenna can cause TVI. Along the way, it elimi-nates tree -climbing, erection of a tower andpurchase of a 2 -acre back yard.

Another important feature is that it tunesthe short-wave bands, unlike many antennasthat simply lie there. Take, for example, thosethat are described in the instruction manualspacked with communications receivers.You'd think after reading the descriptionsthat all it takes is a simple long-wire orcompromise -length half -wave dipole to pullin stations.

Not so, unless the only stations you'reafter are 250 kilowatters like the BBC or theVoice of America. Use an antenna like oneof those to try for Radio Pakistan or OuterMongolia and you just might go to Helsinkibefore you could find them!

In addition to building up signal levels asa half -wave dipole at the higher frequencies-where it counts-our antenna becomes aconventional long-wire antenna at the flip ofa switch.

How's through -the -roof reception? No dif-ferent from that with an outdoor antenna.Radio signals don't know the difference be-tween a fir stud, an asphalt shingle or a holein the wall. So long as the roof isn't made ofmetal, doesn't contain insulation in foil -covered bags, and doesn't have a lot of elec-trical wiring, signals will pass through freely.The important factor is available space. Butread on and you'll see that some of ourdimensions can be juggled to fit the antennainto almost any attic-or even a silo.

The antenna is a multiple dipole. That is,it consists of separate tuned dipoles for fourmajor short-wave bands. You can build theantenna for whatever hands you want. Ourtable shows several short-wave bands, theirfrequencies and half -wave dipole antennalengths.

A novel feature is that all elements of ourantenna are tied together at the center. Thisreduces the number of feedlines to just one,a coax cable, and eliminates bandswitching.The appropriate elements become activenaturally and automatically on the frequencyfor which they're cut.

For those who raise eyebrows at thethought of the multiple connection to thecable and possible mismatching, rest assured.Despite the common connection, the dipolesare decoupled electrically from each other

84

ON,

because of the different lengths. The result isthat each dipole presents about a 70 -ohm im-pedance to the 73 -ohm coax cable.

To keep construction simple we've used apiece of 300 -ohm TV twinlead for each pairof dipoles, or two bands. Both 19 -meter and16 -meter dipoles, for example, are made froma single 31 -ft. length of twinlead.

Building it. First, cut a length of twinleadto the 19 -meter length (30 ft., 6 in.), thencut short one wire in the ribbon to the 16 -meter length (26 ft., 4 in. that is. 25 in. shorteron each end). In similar fashion, cut anotherlength of twinlead for 31 meters (48 ft., 6in.) and cut one wire in the twinlead for 25meters (39 ft., 6 in.).

Now to fit the antenna in your attic. If youhave a ranch -type home with a long attic youmight have room to include a 65 -ft. dipolefor 41 meters. Or, if you inhabit a bowlingalley, there might be room for a real long60 -meter dipole (95 ft., 5 in.). But theseare exceptional cases. Chances are, you'llhave to switch to long-wire, rather than di-pole operation, on these lower -frequencybands.

This explains the function of the knifeswitch shown at the receiver end of the coaxin our diagram. Throwing it to long-wiremeans the coax shield is disconnected fromground and connected to the receiver's an-tenna terminal. The result is a long-wireantenna which picks up energy all along

Board at center where twinlead. coax loin. Di-poles can be added for other bands so long as di-mensions in diagram on last page are adhered to.

Tape wrapped between twinleads provides sup-port and 1 -in. spacing between each pair of di-poles. Space the twmlead with tape every 2 ft.

We suspended our board from rafter, which justhappened to be in center of roof, with a screw -in TV standoff. A home-brew hook will work. too.

85

BILL OF MATERIALS300 -ohm twinlead, as requiredRG59/U coax cable, as requiredTwinlead stand-off insulators, as requiredSPDT knife switchPlastic electrical tape (Scotch No. 33 or

equiv.)23/4 x 5yzin. piece of phenolic, Bakelite or

plastic board, solder lugsCable clamp, 6-32 screws and nuts

the coax, plus the combined dipole ele-ments. In other words, the entire antennainstallation becomes a conventional long-wire antenna.

Long-wire operation on the lower -fre-quency bands won't result in much loss insignal. It is the higher -frequency bands thatneed the benefit of a resonant half -wavedipole. Ample signal should be picked up at41 and 49 meters with the antenna operatingas a long-wire.

Thus, the longest attic dimension requiredfor the antenna we show is about 95 feet forthe 60 -meter band. If you're tight for thisamount of space, here are two possibletions, the first based on the fact that a dipoleantenna picks up most of the signal near itscenter. The ends are mainly for resonatingthe dipole on the frequency for which it's cut.It little disturbs the antenna if both ends dropstraight down for about 20 per cent of thetotal length. For the 31 -meter band this isabout 10 ft., or 5 ft. at each end.

You might push this a little by zigzaggingthe ends slightly but don't overdo it. If a di-pole is bent like a pretzel it will mismatch theline and develop an erratic pickup pattern.The second trick is to bring the dipole endsoutside and down the sides of the house. Inmany attics this can be done through vents orwindows.

Since a dipole is bidirectional, tending tobe most sensitive in the two directions broad-side to or facing the station, give a littlethought to orientation. As one sage said aboutextremely long dipoles and the problem ofdirectionality-simple, just turn the house.Until someone markets a suitable house rotor,there'll have to be some compromise. IfEurope, say, is to the east or west of yourlocation, a north -south running attic wouldprovide the best orientation. But short-wavesignals also have an affinity for taking theshort hop over the poles-which suggests an

SAME ASRIGHT SIDE

2-3/4"X 5-1/2.PHENOLIC

BOARDSHIELD

SOLDER LUGS(4 RED.())

300 -OHMTWIN LEAD

CENTER16M 25MLEAD I9M- 31M

(SEE CHART FOR LENGTHS)

TVSTANDOFFINSULATOR

-\4k

KNIFE SWITCH

(LONG WIRE SWRCVR.

A G

;DIPOLE

Center -board dimensions. Each piece of twinleadcontains two dipole antennas. Slit wire on thelong dimension, then cut off the shorter antenna.

east -west antenna. Again, it's a matter ofcompromise.

Other installation details are shown in thephotographs. TV standoffs and friction tapesupport the elements and eliminate sag. Dur-ing installation try to avoid close proximityto masses of metal which will reduce antennaefficiency. Such things as rain gutters just out-side the roof, plumbing, electrical wiring inattic walls, floor and ceiling wilt affect per-formance adversely. -4-

Short-Wave Bands and Half -WaveDipole Lengths

SW Band(meters)

Frequency(mc)

Total Length(ft -in.)

I I 25.60-26.10 17-9

13 21.45-21.75 21-7

16 17.70-17.90 26-4

19 15.10-15.45 30-6

25 11.70-11.975 39-6

31 9.50-9.775 48-6

41 7.10-7.300 65-0

49 5.95-6.200 78-0

60 4.75-5.060 95-5

86

New! Build a

Gate- DipOscillator

By CLARE GREEN, W6FFS

ASK the ham who owns one and he'll tell you aGDO (grid -dip oscillator) is the most useful

test instrument he has in his shack. For the money, it'simpossible to beat a GDO when it comes to building.

servicing and tuning up transmitters and receivers. Takea look at some of the things it can do:

Serve as a calibrated signal generator. Function as a local oscillator when you are trouble-

shooting a receiver. Indicate a signal's relative strength.

Determine the resonant frequency of such tuned circuitsas filters, traps, antennas. feedlines and such.

Operate as an oscillating detector for making frequencymeasurements.

Work as a modulation monitor.The abbreviation GDO. of course, always has been known to

stand for grid -dip oscillator. But in the last few years GDOs haveappeared on the market that are solid state. This means they have no

tubes and, consequently, there are no grids. Therefore, these instrumentsshould not he called GDOs.

But our solid-state dipper can be called a GDO since the letter Gstands for gate-the control element in the instrument's field-effect tran-sistor.

Basically a GDO unit is a very accurately calibrated oscillator whichincludes a meter that indicates change in grid current. When an externaltuned circuit is inductively coupled to the oscillator's tuned circuit (bothat the same frequency), the GDO's meter indicates a drop. or dip, in gridcurrent. This is because the external tuned circuit absorbs RF energy tromthe oscillator.

Our GDO, a gate -dip oscillator, uses a field-effect transistor in a circuitthat works the same way as a tube GDO. It is completely portable sinceit is powered by a 9-V battery. It is housed in a 51/4 x 3 x 21/s -in. metalbox. Four plug-in coils cover a range of 3 to 60 mc.

How it Works

Take a look at the schematic in Fig. 3. As you can see. the GDO is asimple oscillator (Colpitts) whose operating frequency is determined b),C/ A. CI B and the coil plugged into 31. You tune it over the range of each

87A

J1

Gate -Dip Oscillatorcoil with dual variable capacitor C1. Built-inmeter M I indicates the change in Q 1's gatecurrent.

When an L -C circuit which is resonant atthe same frequency as the GDO is locatednear the pickup coil ( L I -L4), the externaltuned circuit will absorb some of the RF en-ergy generated by the oscillator. As a result,this pulls RF energy from the GDO and Q l'sgate current drops. Consequently, M I willindicate a lower current.

The RF produced by the oscillator is de-tected in Q l's gate -source circuit. The result-ing DC through gate -leak resistor RI is cou-pled via sensitivity control R2 to M I.

Plug a pair of phones into J2 and you dis-connect M I. This converts the GDO into aheterodyne detector which you can use to de-termine whether or not a receiver's oscillatoris working.

ConstructionBecause of the frequencies at which the

GDO operates, parts placement and wiringare critical. Follow as closely as possible thepictorial and photos when installing compo-nents. So the dial will lie flat against the cabi-net, use flat -head screws and countersunkholes to mount tuning capacitor Cl in themain section of the Minibox. Use spacers ornuts to keep Cl's shaft -bearing housing fromtouching the cabinet. We kept Cl a quarterinch away from the panel in our model.

Mount a I 1/4 -in. square piece of perforated'hoard on the bottom of Cl spaced approxi-mately 1/4 -in. from Cl. Install flea clips on thehoard, then connect and wire the componentsas shown in Fig. 1.

Make sure that J 1 is installed so its outsideshell and ground lug do not touch the cabinet.You do this by first drilling a 5/a-in.-dia. holein the top of the cabinet. Then cut a piece ofcardboard and put it between J 1 and the cabi-net.

Make a bracket for B1 to hold it in place.Cut out the dial in Fig. 4 and cement or tapeit to the panel around Cl's shaft. We used apiece of clear plastic (with a line scribeddown the center and filled with ink) fastenedto the knob as an indicator. Short pieces ofwire cemented to the knob also work.

Refer to the coil detail drawing in Fig. 5.Cut the 4,43 -in. dowels to the lengths indicatedand make slots for the wires where shown.Solder a large ground lug to each phono plug

88

Fig. 1-It's important to install the parts associatedwith Cl exactly where shown on a 11/4 x 11/4 -in.piece of perforated board. Mount the board onCl as shown, keeping it 1/4 -in. away from Cl'sframe with two hex nuts. Cut a 5/s-in.-dia. holefor 11 so its ground lug doesn't touch the cabinet.

Fig. 2-Parts placement in bottom of cabinet isn'tcritical; however, mount tuning capacitor at topexactly as shown. We used a rotary switch for SI.

Fig. 3-Schematic of dip-per. Oscillator is Col-pitts. RF is detected inQt's gate -source circuit.DC signal through gate -leak resistor RI is cou-pled via sensitivity con-trol R2 to meter MI. Usethe sketch of QI (flatside facing you) to iden-tify each of the leads. S G D

al

and fasten the other end of the lug to thedowel with a small wood screw. Slip a shortlength of spaghetti over the coil wire, thenslip the wire into the center connector of eachphono plug. Wind the coils as shown, keepingthe wire tight. Solder the other end of the coilto the ground lug and wrap the entire coil withtape. We used colored plastic tape to identify

E31-9 V battery !Burgess 2U6 or equiv.)C1A,C1B--Two-se:-.tion variable capacitor;

front section: 13.5-365 Agf, rear section:7.6-132 gilt (Lafayette 32 R 1101 or equiv.)

C2,C3-47 µµf, 1,000 V ceramic disc capacitorC4,C7-4.7 µAT 1 000 V ceramic disc

capacitorC5-470 gµf, 1,000 V ceramic disc capacitorC6,C8-1,000 opt 1,000 V ceramic disc

capacitorJ1-Photo JackJ2-Closed-circuit phone jackL1,L2,L3.L4-Plug-in coil (see text)M1-0-50 µa DC microammeter (Lafayette 99

R 5049 or equv.)PL1-Phono plug (4 regd.)Q1 -2N3819 FET (Texas Instruments. Allied.

$3.75 plus postage. Not listed in catalog.)L5-.55 mh RF choke (J.W. Miller 4649.

Lafayette 34 R 8829 or equiv.)R1-10,000 ohm, IA watt, 10% resistorR2-10,000 ohm, linear taper potentiometerR3-120 ohm 1/2 watt, 10% resistorS1-SPST slide switchMisc.-5% x 3 a 21/2 -in. Minibox, perforated

board, flea clips, 3/3 -in. dowel (10 in.).

L5

PHONES

Si

iI

Gate -Dip Oscillatoreach coil and to key it to the appropriate dialscale.

CalibrationThere are three ways to calibrate the dip-

per: the first requires a receiver(s) whichtunes to 60 mc, the second requires anotherGDO, the third requires a signal generator.

If you have an all -band receiver, plug ineach coil and tune the receiver until you hearthe dipper's output signal (the receiver willgo silent). Mark the GDO's dial accordingly.

We used a tube GDO to calibrate our dip-per by placing the coils of the two units neareach other and tuning for a dip. This cali-brates the dipper under a load similar to thatused in actual operation.

The third method is to couple a signal gen-erator's output to the GDO with a two -turncoil of wire connected to the generator's out-put. Plug a pair of phones in J 1. When theGDO is tuned to the generator's frequency.you'll hear a beat note in the phones. Start atthe bottom of the frequency range so youwon't accidentally tune in a harmonic.

The number of turns for each coil is ap-proximate and may have to be changed de-pending on how you wire your unit. Add orsubtract from the specified number of turnsto change the range of each coil to correspondto the frequencies marked on the dial.

Fig. 4-Cut out this dial and pasteit on your GDO. Not only will it bea good starting point for calibrat-ing the instrument, but it will dressit up as well. Colors on each scalecorrespond to colored tape wound oneach coil to simplify finding the cor-rect scale for each coil. You may findthe dial's calibration is a bit off whenchecking the unit against anotherGDO or receiver. This is because ofslight differences in coil construc-tion and layout and easily can becorrected simply by adding or remov-ing a few turns of wire from each coil.

START OF WINDING

1+--- L1 2-1/2; L2 -L4 - 2( L4 SHOWN )

PHONE PLUG

SLOT FOR WIRE 318. WOOD DOWEL

Lt -(GREY) 3-7 MC. 120 T. Na 28 ENAM. WIRE

L2-(YEL) 7-14 MC 30 T. No. 28 ENAM. WIRE

L3- (GRN) 14-30 MC 18 T. Na 20 ENAM. WIRE

L4- CORO 30-60 MC 5 T. Na 20 ENAM. WIRE

Fig. 5-Coil details. Colors refer to tape, wrappedaround wire, we used for fast identification.Plug is held on dowel with a large ground lug.

The way to use the dipper to check a coilis to adjust sensitivity control R2 so M 1 indi-cates near to full scale. Sensitivity control R2should be turned full clockwise when usingthe highest -frequency coil (30-60mc). L4.This is necessary becatise at this frequencyQ1 is less efficient and M I will not indicatefull scale. However, the dip will be as appar-ent as it was at lower frequencies.

With the power off and phones plugged in.the dipper can be used as a tuned detector forchecking the output of transmitters. Be care-ful not to apply too much RF to the dipper oryou may burn out the FET. Check the RadioAmateur's Handbook, published by theARRL, for other ways to use a GDO.

1112

MC

YEL

13

14

GRY YELORG GRN

30

6025

502019

GRN ORG

911

SignallnjectorTroubleshooting is a snap with this 600 -cps to 30-mc signal generator.

By CHARLES GREEN, W3IKH

IT always comes as a blow when you dis-cover that the dead tubes in a radio or

amplifier check out good. Don't kick the tubetester! Chances are, it's telling the truth. Whatnext? Only one thing-you've got to get intothe circuit to find the defective stage and com-ponent.

But you don't need a shop full of test equip-ment to do this. Our signal injector, with thehelp of the inoperative equipment itself, willenable you to pinpoint the trouble in a mat-ter of minutes.

Heart of the seven -component injector isa unijunction transistor which generates abasic 600 -cps signal. This frequency is idealfor audio work. Harmonics up to 30 me areproduced by the circuit for troubleshootingRF stages. The injector is housed in an easy -to -hold, inexpensive plastic toothbrush case.

How the Unijunction Transistor WorksBefore we get to the construction and use

of the injector, let's see how the unijunctiontransistor and the circuit work.

A unijunction transistor basically is a diodeto which an extra connection is made (forthis reason it first was called a double -basediode). As shown at the left in Fig. 1, thetransistor consists of a bar of doped siliconto which connections are made at the ends-called the bases ( B1 and B2). In the centerof the bar there's a semiconductor junctionwhich forms the emitter (E).

The silicon bar acts like a resistance; there-fore, if a voltage is applied across B1 andB2 current will flow through the bar. Assumethat the voltage applied to B2 ( positive) andB1 (negative) is 20 V. Because the bar's re-sistance is uniform, the voltage at the P -Njunction will be 10 V positive with respectto base Bl.

Apply another voltage ( + to E, - to B1)that is less than 10 V to the E/ B1 junctionand the junction will simply be reverse biased.

P -TYPESILICON P- N

JUNCTION

BI

N -TYPESILICON BAR

CONSTRUCTION

B2

001611SECMOO CPS)

2.55

B2

RB2

E

P -NJUNCTION

BI

EQUIV. CIRCUIT

RBt

Fig. 1-Simplified diagram at left shows construction of unijunction transistor. In equivalent -circuitschematic at right, diode represents P -N junction between emitter and bar. RBI and RB2 represent resistmice of doped -silicon bar. Injector's fundamental output (center photo) is 600 -cps, 4-V (P -P) spikes

Probe -Size

Signal InjectorOnly a small reverse current will flow in theE/ B1 junction. (Schematic at right, Fig. 1.)

But apply a voltage ( with the same po-larity ) greater than 10 V to E/ B1 and aheavy current will flow through the E/ BIjunction because it is forward -biased. The re-sistance of the bar between E and B1 willdrop abruptly to a low valth

This, in turn, causes the resistance of thebar between B I and B2 to decrease markedly.As a result a heavy current flows through thebar from B I to B2. When the voltage is re-moved from E, the bar's resistance increasesand the current flow from BI to B2 returnsto normal.

ake a look at the injector's schematic inand the voltage at ()I's emitter ( the junctionFig. 3. When SI is closed. C2 begins to chargeof R2 and C2) begins to rise. When col's crit-ical firing voltage is reached. ()I's E/B I junc-tion conducts and discharges C2. This causesa sharp current pulse to flow through R 1 andLI. The pulse is fed through CI to PLI.

The values of R2 and C2 cause the pulsesto he produced at a rate of about 600 per sec-ond. (The frequency can he raised or low-ered by changing the values of R2 and C2.)Because the pulses are sharp they are rich in

PARTS LIST

B1-8.4 V mercury battery (Burgess H126 orequiv..

C1-.005 kf, 1,000 V ceramic disc capacitorC2-.I 200 V tubular capacitorLI-1 mh subminiature iron -core

(J.W. Miller 70 F103A1. Allied 61 Z 885. 754plus postage. Not listed in catalog.)

PLI-Phono plugQ1 -2N2160 unqunction transistorRI -47 ohm, 1/2 watt, 10% resistorR2-18.000 ohm, /2 watt, 10% resistorS1-SPST slide switchMisc.-plastic toothbrush case, perforated

board. flea clips

harmonics-this is why the injector's outputgoes up to about 30 me

ConstructionOur model is built in a plastic toothbrush

case which can he obtained at drug or varietstores. The component layout is not criticaland may he changed to suit any housing.

Cut a hole in one end of the case to ac-commodate the neck of phono plug PL I

.

Carefully solder a ground lug on the neck ofthe plug inside the case. Solder a length ofinsulated wire to PLI's center pin. Mountslide switch SI at the right end of the lidPosition the battery temporarily near theswitch to determine the remaining space. Cuta 234 x 3/4 -in. piece of perforated board tofit in the left side of the case.

Mount the components shown in Fig. 2 on

9.

PL I CI LI RI

Fig. 2-Diagram above shows location ofparts on a 2% x 3/4 -in. piece of perforatedboard. Layout isn't critical; you may changeit to suit whatever enclosure the injector isto be built in. Board is held in place byground lug fitted over plug PL1's neck andsoldered to flea clip in upper left corner ofboard. Use flea clips for tie points for parts.

E

012142160

(BOTTOM VIEW )

Fig. 3-Injector schematic. When Si is closed, voltage builds up across C2 until E/B1 junction conducts.C2 then discharges and sends a pulse through LI. Pulse is rich in harmonics and output goes up to 30 mc.

the perforated hoard with flea clips, theninstall the board in the case. Connect PL1'sground lug to a flea clip on the board to pro-vide mechanical support for the board. Makesure the connecting wires to S1 are longenough to allow the case to be opened easily.

Do not use a low -voltage capacitor for Cl.The reason we used a 1,000-V capacitor forCl is to prevent the injector from being dam-aged should you touch PLI accidentally to apoint in the circuit at which there is high-voltage DC. A low -voltage capacitor wouldbreak down and most likely would destroy theunijunction transistor.

Operation

The output voltage of the injector dependson the impedance of the stage to which it isconnected. Without a load, the amplitude of

the pulses is 4-V, P -P, as shown in the photoin the center of Fig. 1. The injector's outputimpedance is high, which means it will workbest with high -impedance tube circuits. It can-not he used to check, say, speakers.

The way to use the signal injector is toplace PL1's center pin on the grid or base ofa tube or transistor (with the volume controlat maximum gain) and listen for the signalin the speaker. Always start, in the case ofa radio, near the output and work your wayback toward the input. When the signal dis-appears, you have located the inoperativestage.

For some RF and low -gain audio circuits,the level of the signal from the injector canbe increased by touching your finger to PL1'soutside shell or by connecting the shell tothe chassis.

).3

STAMPOUT

MOBILENOISE

By CHET STEPHENS YOUR transceivermay he a deluxe job

with RF and IF noise limiters, but when itcomes to suppressing mobile noise, it maysimply spin its wheels like those of a car stuckin snow. Although built-in noise limiters re-move most annoying clicks and pops, thereoften remains a continuous noise backgroundwhich is stronger than the desired signal.

For example. considering today's super -performance transceivers, a 10 -microvolt re-ceived signal is considered of moderatestrength. Yet the average car's mill can easilygenerate 20 to 50 microvolts of hash, clicks.pops, crackles and other assorted roars! Ob-viously, any CB signal weaker than the noiseis going to he buried. But mobile noise iseasily eliminated providing you know whereit comes from. Names and addresses of sup-pliers of the noise -suppression devices wewill he talking about are at the end of thisarticle

There are two types of noise: The mostannoying is radiated interference caused bythe making and breaking of current flow.Points generate RF noise when they breakthe coil's current. Plugs, producing sparks ofseveral -thousand volts, are great noise gen-erators. They're just like old-time spark trans-mitters which used a spark to generate radiosignals. In a car, a spark produces RF in-terference which is broadcast by the car'selectrical wiring. Best way to get rid of radi-ated noise is simply to prevent it from beingradiated.

The second type of noise is conductednoise-noise carried by the wiring, ratherthan radiated by it, directly into the trans-ceiver. This noise can be eliminated by goodsolid grounds. The first thing to do is toidentify the noise so you know how to attack

it. Filtering a lead that contains or radiatesno noise simply wastes money.

Where's The Noise? Turn on the trans-ceiver and drive the car at a moderate speed.Let up on the gas and turn off the ignition.While you're coasting to a stop, notice if thenoise stops. If it does, the problem is in thealternator (we'll refer to generators as alter-nators here) / regulator system. If the noisecontinues, but at a lower volume, the problemis in both the ignition and alternator/ regu-lator systems.

Ignition noise is a popping, or sputting.sound which varies with the engine's speed.Race the engine and note if the sputting speedincreases. Alternator noise sounds like a

whine. If you're not sure which is which toslipping off the alternator drive belt. With theengine running, a reduction in noise pointsto the alternator/regulator. If the noise per-

LUMP RESISTANCE OR CARBON -RESISTANCE MIRE FEED -TNRUCAPACITOR

Fig. 1-Completely suppressed ignition system.Resistance plugs may be substituted for resist-ance suppressor at top of plug; retime engine.

9-

sists you've got ignition interference. Roarsand crackling sounds point to tie instru-ments: a gas gauge or an electric clock.

Generator noise is easily suppressed witha tuned parallel -resonant network which pre-vents the 27-mc noise components from get-ting into the ignition wiring from which itis radiated. The filter is connected in serieswith the generator's armature

Many cars are factory equipped with a gen-erator filter, which is a bypass capacitor fromthe armature lead to ground. Although thesefilters are effective at broadcast frequencies,they are next to useless at 27-mc and shouldbe replaced with a shielded capacitor or atuned trap.

For an alternator a tuned trap night work.but the more costly alternator fi'ter is the

SIDEVIEW

1/16 -IN HOLESFOR Cl B C23/8 -IN. HOLEFOR GROMMET

TOP

FEED -0Tilt .600CAPACITORS

Fig. 2-To filter regulator, mount it on L -bracketand route A and B leads through coax feed-thru capacitors. Filter F lead with R/C network.

Fig. 3-Top. If your car does not have resist.ance plugs or resistance -wire plug cables, a car-bon noise suppressor must be added at eachplug. Left. All primary ignition leads includingthe feed to the high -voltage coil should be fil-tered with coax shielded capacitor. Make cer-tain all of the connections are good and tight.

better thing to use. This device filters justabout everything but DC charging current.

Regulator noise, caused by arcing ( spark-ing) at the regulator contacts, sounds like asteady, even -volume crackling that you hearonly when the regulator is working. Suchnoise must be filtered by brute force-witha shielded feed-thru coaxial capacitor in the

and A ( armature) leads. The F(field) lead cannot he filtered by a coaxialcapacitor without causing damage to the reg-ulator. Instead, the F lead is bypassed toground through a .002-0 capacitor in serieswith a 3.9 -ohm, 1 -watt carbon (not wire -wound) resistor. These components can heinstalled on an L -bracket as shown in Fig. 2.As a general rule. alternator regulators arenot as noisy as generator regulators.

Should the regulator continue to radiatenoise, as evidenced by failure of the filtering.your only recourse is to shield the regulatorand filters in a metal cabinet firmly attachedto the car body. If you haven't the inclinationto make the enclosure you can purchase ashield assembly complete with filters from theHallett Mfg. Co.

Crushing the Snaps, Crackles and Pops.Ignition noise means all out war. While mostcars have resistance spark -plug wiring to sup-press the ignition noise, it is generally inade-quate at 27 mc. And even if your car hasresistance wiring, resistance suppression verywell may be required. Resistance suppressorsare simply resistors mounted in a plasticholder and installed in each plug's wire. Thispoint is important: The suppressors must beinstalled at both ends of the wire to eachplug. As a general rule. American cars

9

made within the last 5 years use resistancewires. If in doubt, check with the car manu-facturer, the local distributor, or your favor-ite mechanic.

The spark at the distributor, caused byarcing at the points is primary source of ig-nition interference; therefore, each distributorwire must be suppressed. Connect a 10,000 -ohm suppressor between the rotor wire (theone in the center) and the wire socket at thedistributor. Install a 5,000 -ohm suppressorat the distributor between each stator ter-minal and the wire to the spark plug. Placea 5,000 -ohm suppressor at the end of eachplug wire. Or, you may replace your plugswith resistor plugs and eliminate the suppres-sor at both ends of the plug wire. But, youmust retime the engine when suppressors areadded to the ignition circuit.

The ignition coil, even though it can be in ametal can, will generate noise. Be certainit is firmly connected to the car frame. If nec-essary, connect a metal strap from the coilcase to the frame. We also suggest that theinput lead to the coil he filtered with ashielded (coax) capacitor.

Once the ignition coil, distributor and itsleads are filtered, there's nothing more youcan do to reduce ignition noise except toshield all the wiring. This step is a bit expen-sive, but if the previous treatment hasn't re-duced the noise to almost zero, it must bedone to get dead silence. Prefab shielding isavailable from Hallett and consists of shieldedwires for the plugs, plug shields, a shield forthe distributor and a shield for the coil.

Once you've crushed ignition and alter-nator noise you're almost home. All that'sleft is to suppress noise generated by the in-struments. This is easily done by connectinga coaxial capacitor across each gauge and theclock.

A final note, the little ball at the tip of thecar radio's antenna is not a decoration. Itdrains off static charge accumulated in theantenna as the antenna moves through the air.Without the ball you will hear popping sim-ilar to ignition noise, but not as consistently.If you lose the ball it must he replaced. Anyvs -in. or 1/2 -in. dia. plastic ball will do-itdoesn't have to he metal.

Special Noise -Suppression Componentsare available from several places. The 0.1 uf,

Fig. 4-Complete noise -suppression kit. includingshields for distributor and coil. is made by Hal -

let. Note shielded leads, covers for each plug.

600V feed-thru shielded coaxial capacitors(Cl and C2, Fig. 2) are Sprague Type 80P3.They're available from Allied Radio (StockNo. 43 D 5689. Not listed in catalog.) Priceis $1.77 plus postage.

Plug suppressors are Erie's ( Erie Techno-logical Products, Inc.) L7V R-10 M E ( 10,000ohms) and L7VR-5ME (5,000 ohms). Theseare not generally stocked and will have to beordered through your regular electronic -partsdistributor.

A generator filter is available from AlliedRadio for $2.35 plus postage. The stock No.is 17 A 8512. Other noise -suppression partsare on page 480 of Allied's catalog. A basicauto/marine-engine noise -suppression kitcontaining a full set of suppressors and filtercapacitors and shielded generator cable isavailable from Lafayette Radio. The stockNo. is 42 R 0905. It's on page 145 of Lafa-yette's catalog and the price is $9.45. And onthe same page you see a generator -noise filter,voltage -regulator filter and feed-thru capaci-tors.

A complete noise -suppression kit, includ-ing shields for the distributor and coil isavailable from the Hallett ManufacturingCo. Ash at Regent, Inglewood, Calif. 90301.The firm can also supply a shield box contain-ing filters for a voltage regulator. Write stat-ing the make of your car, the year and thenumber of cylinders and they will send youthe price and further information.

Using the methods just described, youshould he able to get rid of that persistentnoise once and for all. It will take a littlework, but there's no other way out.

96

CAL

0100114106

AlWane Audio MixerONCE the initial thrill of recording is

over, the owner of a tape machinequickly realizes that a single mike input foreach channel imposes severe limitations. Forexample, amateur musicians-even goodones-may sound like the kindergarten fifeand wood -block corps when they are re-corded in a living room and picked up by asingle mike.

For professional -sounding tapes, you'vegot to be able to mix several sound sources.More than one mike is needed if you're re-cording a group of musicians or even a singerand accompanist. And if you're trying to re-cord a group conference you need more thanone mike or the group will sound as thoughit is meeting in a cave. To do all these thingsyou need a mixer-a device that combinesthe outputs of several microphones, of a rec-ord player and of high-level inputs such asanother tape recorder.

Our solid-state mixer has four low-leveland two -high level inputs. Any combination

of program sources can be mixed into a sin-gle output. There is a level control for eachinput. To insure proper output level, themixer is equipped with a VU meter and ahigh-level headphone -monitoring jack. Tomake the mixer portable and hum -free, thecircuit is battery powered. The VU meterdoubles as a battery -condition meter.

Note in Fig. 2 that the input transistors areFETs (field-effect transistors). This meanseach channel's input impedance is high. Infact, almost as high as that of a vacuum tube.which means you can use crystal or ceramicmikes with the mixer. The input impedanceof each mike channel is determined by R 1.R5, R9 and R12, which are 2.2 megohmseach. You may increase or decrease the valueof these resistors to match the impedance ofthe mike.

For normal operation, capacitors C1, C2.C3 and C4 do not have to be installed. With-out these capacitors the overall gain is about5db at three-quarters settings of the level con -

Fig. 1-In pictorial, the follow-ing parts are mounted on topof board: all transistors, C9,C10,C12,C13,C15,R211 and R31.All other parts are mountedon back of board. Board ismounted on Ml's terminals.

All -Purpose

Audio Mixer

trols. This means that if your mike has anoutput level of-50db the signal at the mix-er's output jack will be-45db. Without thecapacitors the frequency response is almostruler -flat from 10 to 20,000 cps. Distortion atnormal mike levels is almost unmeasurable.

At input levels as high as .03 V (rms), dis-tortion without the capacitors is slightly lessthan 1 per cent. If you need a little extra gain,an additional 5db to 7 db can be obtained byinstalling Cl, C2, C3 and C4. With them in

the circuit, response will be flat from about 40to 20,000 cps. Distortion at normal mike lev-els will be about 0.5 per cent. High-level sig-nals (0.3 V rms) into J1 through J4 then willproduce distortion somewhat in excess of Iper cent.

You can build the entire mixer or any partyou want. For example, if you don't need aVU meter, drop off all the components asso-ciated with Q5, Q6 and Q7 (this includes C9and R32). The VU meter can be retained as

git

IMIKE I.]

a battery -condition indicator or it, too, can bedropped off, thereby eliminating R31. R32and S2. If you have no need for high-level in-puts you may drop off J5 and J6. Then con-nect C7 to R17 and C8 to R20. If youneed only a two -channel mixer drop off allcircuitry associated with Ql and Q2.

Before getting into construction note thatQ1 thru Q4 have a negative ground-theirsources (S) are connected to ground via R3.

R7, RI 1 and RI3. The positive supply feedsR2, R6, RIO, and R14.

On the other hand, Q5 thru Q7 have apositive ground. That is, the emitters are re -

PARTS

131,82-9 V battery (Burgess C6X or equiv.)Capacitors:C1,C2,C3,C4,C11-30 µf, 6 V electrolyticC5,C6,C7,C8,C9,C12-.1 ;if, 75 V ceramic discC10--10 gf, 15 V electrolyticC13-30 gf, 12 V electrolyticC14-160 µf, 15 V electrolyticC15-50 if, 25 V electrolyticJ1,J2,J3,J4,J8-Phone jack (see text)J5,J6-Closed-circuit phone jackJ7-Phono jackMI-VU meter (Lafayette 99 C 5043)Q1,Q2,Q3,Q4--HEP-801 transistor (Motorola.

Allied HEP-801. $3.39 plus postage)Q5,Q7-HEP-250 transistor (Motorola. Allied

HEP-250. 79¢ plus postage)Q6-HEP-252 transistor (Motorola. Allied

HEP-252. 89¢ plus postage.)Resistors: 1/2 watt, 10% unless otherwise

LIST

indicatedR1,R5,R9,R12-2.2 megohmsR2,R6,R10,R14-560 ohmsR3,R7,R11,R13-6,800 ohmsR4,R8,R17,R20-500,000 ohm, audio taper poten-

tiometer with SPST switch (Lafayette 32 C 7288)R15,R16,R18,R19,R28,R31-100,000 ohmsR21,R27-470,000 ohmsR22,R29-4,700 ohmsR23-120,000 ohmsR24,R25-10,000 ohmsR26-1,500 ohm, linear taper potentiometerR30-470 ohmsR32-3,600 ohms (supplied with MI)S1-SPST switch on R4S2-SPDT toggle or slide switchMisc-Perforated board, 9 x 6 x 5 -in. aluminum

utility cabinet (Premier AC -695 or equiv.),shielded wire, flea clips

R2

Fig. 2-Complete schematic. On Qi through Q4, lead between Dand S is C (case): it should be connected to ground. For a stereomixer, duplicate all circuitry except power supply and VU meter.

Jl G (.."\_,...-

CS R4 RI5-=- 11.".E-VE7-Cil 4--9-0\AN-e--

R3

R8RI6

(LEVEL 2]

RIB

- 4-1/V4-*ILEVEL--

HIGHLEVEL

J7

QFUTR28

CI4 eR30eT

SI

,1 , F__0).-°_,EH 82

IBATI

R31 S2

CIS _L_

HEADPHONEMONITOR

HIGH-LEVELOUT

VU

R32

J8

99

All-PirposeAudio Mixer

Fig. 3-Photo at top isof top of circuit board.Photo at bottom is ofunderside of board.Triple -check your wiringas it will be difficultto remove the board tocorrect an error afterthe board is installed.

turned to the positive supply voltage, which isnot connected to the chassis. Also note thatthe collector resistors of Q5, Q6 and Q7 areconnected to true ground-the chassis-bat-tery negative. Do not mix up the chassisground connections.

Construction. Our mixer is built in a9x6x5-in. aluminum utility cabinet-actuallyon the front and rear panels. The resistors,capacitors and transistors are mounted on apiece of perforated board on which flea clipsor Vector T28 push -in terminals are used fortie points. All resistor and capacitor valuesare critical and no substitutions should bemade. If money is no object, we suggest youuse low -noise deposited carbon or film -typeresistors for RI, R2, R3, R5, R6, R7, R9,R10, R11, R12, R13 and R14.

Start construction by mounting all thefront -panel components. Install level controlsR4, R8, R17 and R20 and put monitor jackJ8 as close to the bottom panel edge as is pos-sible. VU meter M1 should be mounted closeto the top panel edge. Install Bat. VU switchS2 and VU Cal. control R26 between MI andthe edges of the panel about 1/2 in. aboveM I horizontal center -line. Orient level con-trols R4, R8, R17 and R20 so their terminalspoint straight up as shown in Fig 1.

All controls are shown with a switch be-cause the type specified in the Parts Listcomes with a switch and sells for half theusual price.

Next, install the rear -panel jacks and ametal bracket, made from scrap aluminum,to hold the two batteries. To keep costs downwe show standard open -circuit jacks for J1through J4. To avoid open -circuit noise, wesuggest you use shorting -type jacks whichwill automatically ground the input when the

mike plug is removed. High-level jacks J5and J6 are closed-circuit jacks that automati-cally disconnect mike amplifiers Q3 and Q4when high-level plugs are inserted.

Cut a 2 x 73/4 -in. piece of perforated board.Notch the board as shown so that S2's termi-nals are in the clear. Before mounting anycomponents on the board, install positive andnegative buss wires across the full length ofthe board. The buss in the center of the boardis the battery negative, or ground buss. It isconnected to cabinet via J1's shielded lead.Next mount Q1 through Q4 and associatedcomponents. Resistors R15, R 16, R18, R19,R3I and R32 are installed after the board ismounted on the meter terminals.

Use a 25- to 35 -watt iron and use a heatsink, such as an alligator clip, on each tran-sistor and resistor lead when soldering. Toprovide clearance for the meter case, keepthe components on the underside of the boardflat against the board.

Fig. 4-Completed mixer. Note home-brew bracketwhich holds batteries. 12 -in. leads to all lacksallow for easy installation of panels in cabinet.

100

After the board wiring is completed, installthe board on the meter terminals as shown,using the hardware supplied with the meter.To provide clearance for the board compo-nents install a set of nuts on the metal termi-nals and then place the board over the ter-minals. Place the meter solder lugs on top ofthe board, install the original lockwashers,and then mount and tighten the mountingnuts. Complete the wiring to the front -panelcomponents. Resistor R32, the meter multi-plier, is provided with the meter.

The shielded leads from the front to therear panel are 12 -in. lengths of RG-174/ Ucoax. Note that only the cable connected to11 has the shield connected at both ends. Oneend is connected to 11's ground lug and theother end is connected to the board's groundbuss. The remaining cable shields includingthe cable to J7 are connected only to the cir-cuit -board ground buss. Tape the jack end ofthe cables to prevent a strand of wire fromshorting the cable.

Using the Mixer. Connect the mixer via17 to your tape recorder's mike input withshielded wire. Connect the mikes to jacksto J4. Set your recorder's volume control tothe normal setting, then advance the levelcontrol of the channel to which a mike isconnected and speak into the mike. Advancethe mixer's level control until the recorder'svolume indicator shows the usual or normalrecording level. While still speaking, advanceVU Cal. control R26 until MI indicates thesame level on speech peaks as the recorder'slevel meter. Then, tape or lock (with a shaftlock) R26 so it cannot be accidentally

When the board is completed. itis installed on top of the meter,and final connections are madebetween the board terminals andall the front panel components.

changed. If you have an AF signal generator,a more accurate adjustment of M I can bemade. Set the recorder's level control to nor-mal, feed a 1,000 -cps signal at about-45dbinto J I and advance R4 until the recorderlevel meter indicates peak recording level.Then adjust R26 until M1 indicates 0 VU.Then lock R26.

Up to four microphones can be mixed si-multaneously. You can also mix a high-levelsignal, such as from another tape recorder orceramic cartridge, by connecting the high-level source to either J5 or J6. Note that thehigh-level source kills the mike input asso-ciated with it. For example, connect a high-level source to 15 and you will disable themike plugged in J3.

The signal level at jack J8 is more thanadequate for a comfortable headphone vol-ume. Use headphones rated at 2,000 ohmsimpedance or higher-crystal phones arerecommended. The level at 18 is about I V,rms. You can connect the output at this jackto any high-level amplifier input' designed toaccept a 1-V signal. However, distortion andnoise level at J8 are slightly higher than at J7.

With power switch S1 on, setting S2 to thebat side will cause M I to indicate the batterycondition. As long as the meter pointer indi-cates in the red region above the 0 VU mark,the batteries are okay. Depending on theFETs you use, the batteries may still be usa-ble when the pointer falls below 0 VU. Don'tdiscard the batteries if the pointer falls below0 VU. Wait until you can just about hear orstart to measure an increase in distortion orsharp loss in gain. +

101

CB

CONTROL

CONSOLEBy LEN BUCKWALTER, KBA4480

IT gets tiring when you have to do thewatusi every time you check out your CB

rig. First you connect one antenna, then dis-connect another and . . . well, you knowhow long that can go on.

But mount your rig on our CB ControlConsole and you'll be able to sit back andsimply twist switches. The console places atyour fingertips a half -dozen different meas-uring instruments. No need to haul out a lotof separate meters and connecting cableswhen a turn of a switch lets you see every-thing from antenna efficiency to transmitterpower and modulation. And you won't needyour rig's schematic to hook up the console.It just plugs into the antenna socket.

The console is designed for convenience.First, it raises a set off the table, makingknobs a snap to grasp and turn. And thepanel meter will be elevated so numbers areeasier to read. The slight tilt upward aimsthe panel at your eyes, not your tummy.There are other benefits, too. You can store

47"

19"

.Z3

PL I1

S2 -OHM BRAID N.26 ENAMELED -WIRECOAX PICKUP LINK

Fig. 1-Top diagram shows how to prepare a 47 -in.length of coax for pickup link. Sketch at rightshows how to bunch braid to insert the piano wire.Pull braid tight after installing the pickup link.

crystals and other small items under the con-sole and there's an antenna -selector switchthat lets you connect to either of two out-door antennas.

Then there's a field -strength meter to en-able you to tune up a rig or check its output.A built-in dummy load lets you work on atransceiver without radiating a signal. Finally,the console will make your set look less likea table radio and more like a communica-tions center.

Construction

The console's panel must be a sturdy pieceof metal. You can save a lot of work by usinga standard 51/4 x 19 x Va -in.-thick aluminumrack panel. Using a hacksaw, cut the panelwidth to 14 in. Most difficult cut to make isthe 21/2 -in-dia. hole for the meter. Cut it bydrawing a circle on the panel, then drill aseries of small holes on the circle until thecenter piece drops out.

The two legs for the console are heavy

N.26 ENAMELEDWIRE

COAX BRAID

PULL THROUGH

MUSICWIRE

102

strips of 3/4 in. -wide aluminum. Bend thestrips as shown in Fig. 2 and drill holes forNo. 6 mounting screws. The support plat-form is a piece of 8 x 113/4 x t/8 -in. -thickMasonite. This size should support just anyset. At the rear of the console is an L -shapealuminum bracket for antenna sockets SO1and SO2. Holes for the sockets can be madein minutes if you have a 5/8-in-dia. socketpunch.

The Pickup Link. The installation of aI3 -in. pickup link inside a length of coaxialcable requires patience and care. Purpose ofthe link is to take a sample of RF energy tooperate the console's SWR meter (to meas-ure antenna efficiency). To make the link,

Fig. 2-Rear of console's con-trol panel. Note how coax withthe pickup link is routed fromupper -right cdrner, wherebraid is soldered to groundlug, around the meter anddown to lower -right corner.Braid is not grounded at endbut is soldered to the braidof coax cable coming fromthe rotary selector switch, S2.

take a 47 -in. length of RG58/ U coaxial cableand install PL I at one end. Then prepare thecable as shown in Fig. 1. Note that you stripaway 19 in. of the black plastic jacket. Dothis with a razor blade, being careful not tonick the braid.

The link is a piece of No. 26 enameledwire inserted between the braid and the in-sulation around the center lead. Since theNo. 26 wire is flexible, you'll have to use astiff piece of wire to snake it through, asshown in Fig. 1. Start by pushing the braidtoward the cable's jacket to get it to bunchup. Insert through the braid a stiff piece ofwire, such as piano wire, 2 in. from the in-sulation and push it through until it exits at

103

(REV.

SIA

C2

IV PICKUPLINK

R2

SIB

FWD.]

-0

R7 Re

D415 IR6S2/

DPI

8P2

S2 POSITIONS

0SOI

42A

502

1ANT.2

I

2- LAMP- RP WATTS

f,alLt

I3

5

- MODULATION- CALIBRATE- ANT. I TI BASE

6 - ANT. 2IFSM.i

SSC3 C

IANT.I 1

(Nom I

I AUDI 0

Fig. 3-Connect PL1 to rig's antenna connector and connect audio jack

CB

CONTROL

CONNIE

a small hole in the braid13 in. away. Once thewire is through, attacha length of No. 26 en-ameled wire to it andpull both wires throughand out. Scrape the in-sulation from the endsof the enameled wireand it's ready to be sol-

dered to the appropriate points.Note in the pictorial in Fig. 2 that the

braid is soldered to several solder lugs whichare grounded to the panel. There are two atthe top of the meter, one above R9 and onenear S3. At the end of the cable that connectsto a terminal strip at the lower right, thebraid must be pulled back, twisted and sol-dered to the braid of the other coax cablewhich also connects at this point. The braidsare not soldered to ground at this end. Thesame treatment is given to the coax braidsnear S2. These two braids are grounded un-der the metal clamp next to pilot lamp P 1.Note that one lamp wire also goes to thispoint and is soldered to both clamp and coaxbraids

12 to the transceiver's speaker.

Protective Jumper. There's one importantprecaution to take if you intend to operatethe console with only one antenna. You mustinstall a short piece of hookup wire (secasterisk in Fig. 3) between terminals 4 and6 of S2B. Switch S2 can select one of twoexternal antennas. If you hook up only oneantenna you accidentally might switch to theunused antenna socket with the transmitteron. This would not bother a tube rig butlack of a load on a transistor job might causedamage. The jumper prevents accidents. Ityou mistakenly switch to ant 2 ( the unusedsocket) a dummy load automatically will beconnected to the transmitter. Of course thejumper should be removed when you connectanother antenna

Installation

Place the CB rig on the console's platformand connect PLI to the set's antenna socket.If one external antenna is used, connect it toSO 1. This corresponds to the ant I positionof switch SI . The other socket is for ant 2.

Since the CB rig is at an angle, it may tendto slide toward the rear of the console. Thiscan be cured with the backstop shown in

PARTS LIST

BP1,I3P2-Five-way insulated binding postC1,C3,C5-.005 µf, 1,000 V ceramic disc

capacitorC2-4 at. 50 V electrolytic capacitorC4-.1 at. 400 V tubular capacitorD1,D2,03,D4-1N60 diodeJ1,J2-Phone jack11-2.5 mh RF chokeM1-0-50 µa microammeter (Lafayette 99 C

5042 or equiv.)P1-No. 47 (6 V) pilot lamp and socketPL1-PL-259 coax connectorR1-33 ohm, 1 watt 10% resistorR2-18 ohm, 1/2 watt, 10% resistorR3-12,000 ohm, 1 watt, 10% resistorR4-5,600 ohm, V, watt, 10% resistorR5-1,000 ohm, I/2 watt, 10% resistorR6,R7,R8-16 ohm, 2 watt, 5% resistorR9-50,000 ohm, linear -taper potentiometer81 -2 -pole, 2 -position shorting -type rotary

switch (Centralab 1462. Allied 56 A 4082 orequiv.)

82 -2 -pole, 6 -position shorting -type rotaryswitch. (Centralab PA -2002. Allied 56 A 4901or equiv.)

S3-SPDT toggle switch801,802-SO-239 coax connectorT1-27-mc antenna coil (Lafayette 99 C 6200)Misc.-RG58/U coax cable, No. 26 enameled

wire, knobs, aluminum panel, terminalstrips

Fig. 5-a piece of weatherstripping coatedwith an adhesive on one side. Now you'reready to put the console into operation.

Operation

Normal. Here's how to set up the switchesfor normal CB operation: set fsm.-norm.switch S3 to norm. Set SI to fwd. and set S2to ant I. Turn R9 full counterclockwise (low-est sensitivity). Start transmitting and turn R9clockwise until M1 indicates about halfwayup the scale.

With the console so set up, it will indicatethe relative power sent to the antenna. Theneedle falls to zero during receive, then riseseach time you press the transmit button. Ifyou wish to tune the output stage of the CBrig the meter becomes an output indicator.

SWR Measurements. Here the consolemeasures overall efficiency of your antennasystem. It can detect trouble, for example,such as broken elements or poor cable con-nections that might originate in the roof an-tenna. Any problem along the line or at theantenna is apt to affect the system's standing -wave ratio (SWR).

To check SWR set up the controls as be-fore. Turn on the CB rig to transmit and ad-just R9 until M 1 indicates exactly full scale.

Fig. 4-To peak T1. supported by soldering itslugs to terminal strip, set up for FSM measure-ments and adjust the slug with alignment tool.

Fig. 5-Finger points to weatherstripping at backof deck. It prevents rig from slipping off. Theantenna -connector bracket is at the lower left.

Then, with the transmitter still on, flip S1 torev. M1 should drop below 10 if efficiencyis high and SWR is low. If you want to knowthe true SWR reading, the meter scale inFig. 6 (it fits over the scale of the meter speci-fied in the Parts List) gives the three mostimportant values. Any SWR indication under1.5 is fine. It isn't serious if the indicationgoes nearly to 2. But check for trouble if theSWR is anything over 2. Readings over 3

2

0

3

Fig. 6-Cut out and paste over meter's scale.

105

Best way to check your modulation is to listen toyour transceivers output. Just plug a pair ofhigh -impedance phones in jack 11 on front panel.

mean most of your signal is cancelling itself.Such SWR measurements are accurate

enough for most jobs. You simply adjust orrepair the antenna system for lowest meterindication. It's possible, though, to improveabsolute accuracy by changing the combinedvalue of R 1 and R2. You'll need an accuratedummy load of 52 ohms to do this (Lafayette42 C 0902) . Install the load at the ant. 2 socketand measure SWR. Since the load is correct,SWR should fall nearly to zero. If the readingis below 4 (microampere scale on the meter)consider your console accurate enough. Butif the reading is higher you'll need a differentvalue for R2 (specified as 18 ohms) to bringthe SWR down. Try other resistors just aboveand below 18 ohms to see whether you canlower the meter indication. This proceduremakes up for differences in circuit layout.If the reading is below 4 (microamperes scale)you can calculate any SWR by doing the fol-lowing: (I) add the meter indication (in rev.position) to 50; (2) subtract the same meterindication from 50; (3) divide (1) by (2).

Checking Modulation. The console givesa choice of two modulation checks. First iswith the meter. Set S3 to norm., set S1 toeither position; set S2 to calibrate and turnR9 fully counterclockwise. Turn on the CB

transmitter and, without speaking, turn R9until M1 indicates 50. Keeping the transmitteron, turn S2 to modulation and begin talkinginto the mike. The needle now should movein step with your voice. When MI occasion-ally hits about 35, it's equivalent to about 100per cent modulation. The indication is onlyapproximate since meter ballistics prevent aperfect display of modulation percentage; yetthis can serve as a guide. After you're accus-tomed to a given amount of needle move-ment, you'll know when something's amiss.

The other modulation check can be madeby plugging earphones into mod. jack .11.You'll be able to hear speech quality as itwould be transmitted over the air.

RF Power. This test indicates the trans-mitter's approximate output power in watts.Set S2 to RF watts and turn R9 full clock-wise. With the CB set to transmit, MI nowshould indicate transmitter output power di-rectly: that is, 20 on the meter equals 2 watts.30 equals 3 watts, etc. Since this is outputpower, an indication of about 3.5 watts isthe highest you'll see. (During this test, thepower is that developed in the console's in-ternal dummy load and is not RF power de-livered to the antenna.)

Visual Output Indicator. A quick checkon output RF can be made by turning S2 tolamp. The red lamp (P1) is a dummy loadwhich is lit by RF power. It should flicker asyou speak into the mike. Note the tally isonly a test position.

Field -Strength Measurement. Built intothe Console is provision for checking sig-nal strength. M1 will respond to a transmittedsignal and indicate its relative strength. Thusthe fsm function is useful for tuning up awalkie-talkie, for example, or a mobile rig.

Set up the console for this function bysetting S3 to fsm. (Note that this is theonly time this switch is moved from norm.Be sure to move it back to norm. after check-ing field strength or the meter will not oper-ate for the other functions.) Attach a 10 -in.length of stiff wire to BPI. With the CB rigtransmitting, adjust Ti's core for highestmeter indication. If M 1 goes off scale, reduceits sensitivity with R9.

Other Functions. Jack J2, marked audio.is a spare that can be wired up according toyour needs. Some possibilities: connect it tothe rig's speaker and you can feed receiveraudio to a speaker in the basement.

4'

BY,

POCKET

CB

CONVERTER

By CHARLES GREEN, W6FFQ

Take one transistor, add a few parts then

tune the Citizens Band on any broadcast radio.

THE original purpose of CB-to maketwo-way radio available to almost any-

one who needed it-has been served. Butthere are often times when only one-waycommunication is required. For example:suppose you regularly have to call the chil-dren in from the ballfield for dinner. In thissituation it is only necessary that you get amessage out to them. They do not have toreply.

Let's say you now have a 5 -watt -stationset up-one rig's at home and the other isin the car. Naturally the mobile is going tobe used by the man of the house duringthe day. It can't be conveniently taken to thegame and operated from a storage battery.

At least you have a transmitter at home toget the call out. But how are the children tohear you? You could provide them with awalkie-talkie, but if it has any kind of sensi-tivity to pick up your signal it will cost atleast $25.

Now most kids these days carry a tran-sistor radio with them at all times. It's asmuch standard equipment as the flask wasto the flappers in the roaring twenties. Ifyou could only use that 5 -watt rig at home tocall them on their radio. That is, if therewere only a way to be able to pick up a

27-mc CB signal on any broadcast radio.It can be done and without modifying

your 5 -watt rig or the radio. You use anelectronic middleman called a converter.Our converter is a simple one -transistor, one -evening project which will set you back lessthan $10. Combined with a' transistor radio(or, for that matter, any radio, it will do abetter job of picking up your signal thanmost walkie-talkies with superhet receivers.Here's the way it works.

You tune the radio to a spot on the dialwhere there's no station, place the radio ontop of the converter and you're in business.You do not have to make a connection be-tween the converter and the radio as the con-verter radiates its signal into the radio. Allyou need is an antenna; the converter is bat-tery -powered for portable operation.

The converter can be tuned to receive anyCB channel. As we said, you merely setyour radio to any quiet spot on the broad-cast dial and do the tuning on the converter.

If you do not have an application for one-way communications as we suggested, usinga converter and a radio is an easy and inex-pensive way to just monitor the band whileyou use your 5 -watt rig for regular commu-nications.

107

FOIL

POCKET

CB

CONVERTER

First, cement a P/4 x 21/2 -in. piece of aluminum foil at left end of case cover. Then install Si. C7 andNext, mount other parts on 4 x 21/2 -in. piece of perforated board. Only L3 goes on back of board. Use3/e -in. spacers between board and cover. Be sure you wind Ll/L2 coils over TI and T2 exactly as shown.

The CircuitTake a look at the schematic. Signals

from the antenna are coupled via jack .1 I tothe primary winding of transformer TI. Theyare tuned by fixed capacitor CI which isconnected across TI's secondary. ( TI istuned to the center of the Citizens Band byCl ). The 2 -turn coil ( LI ) couples the sig-nals via C2 to the base of transistor Ql. Thebase of 01 is also coupled via the other 2 -turn coil (L2) to oscillator transformer T2.T2 is tuned by C6, C7 and C8 so the oscil-lator operates approximately 1 me above thefrequency of the incoming signal. The IF

signal is produced by mixing the incomingsignal with the oscillator's signal.

Construction

Our converter is built in a 5344 x 3 x 11/2 -in. plastic box. A wood or bakelite box canbe used, but you must not use a metal boxas it will prevent the RF from getting outto the radio.

All of the components except C7, J I andSI are mounted with flea clips on a 4 x 21 -

in. piece of perforated board. Before in-stalling the board on the cabinet cover,mount coil L3 on the rear of the board bysoldering its lugs to two flea clips. Space the

108

ANT.

B1

poi

LI L2

4:3

T1 01 T2

B S (CUT OFF)01

BOTTOM VIEW

Incoming signals go to the primary of transformer T1, which is tuned to center of Citizens Band byCl. LI couples signals via C2 to base of Q1 which Is also coupled by L2 to oscillator transformerT2. As T2 is tuned about 1 mc above incoming signal, an IF signal is produced. It's radiated by L3.

board above the box's cover with 3/8 -in.

spacers mounted at the board's corners.Install the parts exactly where shown as

the wiring and spacing of components arecritical. Before mounting any parts on thecover cement or tape a piece of aluminumfoil on the inside at one end of the cover.This will minimize the effects of hand capaci-tance when you bring your hand near C7 totune. Connect the foil to the circuit groundwith the mounting nuts and bushings of C7and 11. Cut off the shield lead of Q 1.

Wind coils L1 and L2 next. They are each2 -turns of No. 22 hookup wire wound on T1and T2 as shown in color in the pictorial.Keep the turns just to the left of the coil lugs.If you wind the turns too close to the exist-ing windings there will be over -couplingwhich will prevent oscillation.

Alignment and Operation

Turn Ti's slug -adjustment screw so 1/4 -in.of the screw is out of the form. Set T2'sslug -adjustment screw so it is 1/2 -in. out ofthe form. Set L3's slug -adjustment screw soit is th-in. out of the form. Set C7 to fullcapacity (full counterclockwise) and placea transistor radio on top of the converterso the radio's loopstick antenna is directlyabove and parallel to L3. Set S1 on on andtune the radio to a quiet spot near 1200 kc.

Connect a signal generator set up to feeda 26.96 mc modulated signal to J1. Tune T2until you hear the signal in the radio and

PARTS LISTB1-9 V batteryCapacitors.C1,C6-47 prif, 600 V tubular ceramicC2,C3.C5-.002 Aif, 1,000 V ceramic discC4-100 AO, 600 V tubular ceramicC7-10-360 AO variable (Lafayette 99 C 6217)C8-10 AO, 600 V tubular ceramicJI-Phono lackL1,L2-2 turns No. 22 hookup wire wound

over T1 and T2 (see textL3-Ferrite antenna coil (J. W. Miller No

6300. Lafayette 34 C 87051Q1 -2N1180 transistor (RCAR1-4,700 ohm, 1/2 watt, 10% resistorR2-2,700 ohm, 1/2 watt, 10% resistorR3-1,000 ohm, 1/2 watt, 10% resistorS1-SPST slide switchTi-Antenna coil, 12.36 mc. (J.W. Miller

13-5495-A. Lafayette 34 C 8720)12-Oscillator coil, 12-36 mc. (J.W. Miller

D -5495-C. Lafayette 34 C 87221Misc.-53/4 x 3 x 1 3/16 -in. plastic box

(Lafayette 14 C 4403), perforated board.

adjust T1 and L3 for maximum volume.Keep the level of the signal from the gen-

erator as low as possible for best alignment.Repeat the adjustment several times. Cementa dial on C7's knob then calibrate the dial.

Disconnect the signal generator from J1and connect a good antenna to J1. For stronglocal signals, a 5- or 6 -ft. length of wire willwork. For best reception, a high outside an-tenna is better. Find a strong signal in thecenter of the band and peak up T1 for bestreception. Other frequencies can be used onthe radio instead of 1200 kc, but this willrequire peaking L3 and T2 again.4.

The Case of the

Buried TreasurePIRATES and plumbers, attention! Here's a device that will boost business. It's ametal locator and it will find everything from buried treasure and hidden pipes to

nails in the wall and hardware in your crackerjacks.Because our locator is not complicated, its sensitivity is somewhat limited. However,

our explanation of how metal locators work will enable you to design your own circuitso you can dig farther for riches-or way in for that elusive hot-water pipe. We'll firstexamine two important circuits used in these devices, then construct a simple, practicalproject.

First circuit is that of a proximity detector-a device once used in wartime to ex-plode a shell at the most effective instant before it hit the target. Take a look at theleft schematic in Fig. 1. It's of an oscillator which generates an RF signal. As the sig-nal flows from tuned circuit to tube grid (along arrow marked normal) it sets up steadynegative voltage on the grid. That's the oscillator's operating bias voltage produced bygrid -leak action. Point is, when the tube oscillates, little plate current flows and the re-lay contacts remain open.

But bring metal near the sensing antenna and the RF signal will be pulled away fromthe grid. Now there's less signal available to produce negative bias; therefore, platecurrent increases. The relay pulls in (and explodes the shell).

This basic detector is also known as the capacity relay. It responds most stronglyto metal, but a hand brought close to the sensing plate will also detune, or load down,the oscillator causing it to energize the relay.

Our second circuit (shown at the right in Fig. 1) is the beat -frequency metal locator.

SENSOR ABSORBEDSIGNAL

NORMALSIGNAL

C

r - -

I

1

1 km -TUNED

___J CIRCUIT

TUBE TOCONTROLLED

CIRCUIT

A-0

Rao

B -f

OSC 1SEARCHCOIL

FIXED-0SCOSC 2 COIL

RF SIGNALS

PHONES

-=.

Fig. 1-Warhead proximity detector circuit, left. Nearby metal pulls signal from grid causing currentto increase and relay to close. Basic circuit of beat -frequency metal locator, right. Metal near searchcoil changes its inductance and oscillator's frequency. Frequency difference produces tone in phones.

1 1 0

Its operation is based on the heterodyne ac-tion between the outputs of two RF oscilla-tors. Such action produces an audible signal.Instead of a relay, you listen with earphonesfor a change in tone, which reveals the pres-ence of metal. Note that Osc. / has a specialloop called a search coil which gets movedover the area being inspected. When it passesover metal, the coil's inductance changes.This shifts the frequency of oscillation.

The other section of the device containsa similar fixed -frequency oscillator whose coilis shielded. Since both oscillators feed the ear-phones, signals mix and the difference is

heard as an audible tone. For example, ifboth oscillators are set to generate a 1,000-kc signal you will hear no sound in thephones. But if the metal near the search coilreduces the frequency to 998 kc, you'll hearthe 2,000 -cps difference frequency.

In a practical metal locator, there's a mixerstage between the oscillators and phones. Al-though the basic circuit shown here can pro-duce beat notes, it's plagued by pulling-achange in one oscillator's frequency tends toshift the other's frequency. The mixer stageintroduces isolation between them.

Our metal locator's design is based on thebeat -frequency principle. The circuit, how-ever, has been greatly simplified by construct-ing just one oscillator with a search coil. Youuse any portable transistor radio to performthe remaining functions-mixing and pro-ducing the tone. The fixed -frequency signalis supplied by a broadcast station.

Start construction by winding the 31/2 -in.-dia. search coil around the perimeter of a

Fig. 2-Our metal locator's oscillator. Search coiland Cl determine frequency. Adjust Cl to produceheterodyne whistle with station tuned on radio.

......... .....

. ..... ,.............. ................... ..... ,.......... ... .. :

Fig. 3-Back of metal locator shows how the searchcoil (17 turns of No. 22 enameled wire) is woundon a 41/2.in.-square piece of perforated board.

41/2 -in. -square piece of perforated boardwhose corners are notched. You'll have toenlarge three holes in the board to mounttrimmer -capacitor C 1 . One center hole is toallow the tuning -screw threads to protrudethrough the board. Two others are for themounting tabs. If the solder lugs on your trim-mer are bent, straighten them so they remainon the component side of the board.

The battery can be taped or glued to thewood handle. You can mount an on -off switchin a free area on the board, if you wish. Inour model we simply connected an alligatorclip to the positive battery terminal.

The operating frequency of the oscillatorfalls in the upper portion of the BC band.If you wish to lower the frequency, eitheradd more turns to the search coil, or connectan additional capacitor ( about 100 p.p.f)

across C I .

PARTS LIST

81-9 V batteryC1-25-280 µid trimmer capacitor (Lafayette

34 C 6832 or equiv.)C2-.02 0, 400 V tubular capacitorC3-100 AO, 1,000 V ceramic disc capacitorC4-.05 f.if, 400 V tubular capacitorQl-PNP transistor, general-purpose RF (GE -1

or equiv.)R1-47,000 ohm, 1/2 watt, 10% resistorR2-10,000 ohm, 1/2 watt, 10% resistorR3-680 ohm, 1/2 watt, 10% resistorS1-SPST slide or toggle switchSEARCH coil -17 turns No. 22 enameled wire

wound 31/2 -in. squareMisc.-41/2-in. square perforated board, 1 -in.

square X 6 -in. long piece of wood

SiALLIGATOR

CL/P

e t

o 0o 0 °

To operate the locator, tune a BC radioto a station at the high end of the band. Next,adjust Cl until you hear steady tone fromthe radio.

As you move the search coil near metalobjects, the tone should vary. Since your handwill also vary the tone (due to body capacity)hold the wood handle at the end.

After a little experience, you should beable to improve your skill. You'll find thatthe tone shifts in one direction for body ca-pacity and in the reverse for metal. If youwish to convert the unit into a complete,portable instrument, devise some simplemounting arrangement for a transistor radioon the wood handle.

As a matter of fact, it would be best tomount the radio on the handle anyway so theradio's antenna always remains in a fixed po-sition relative to the search coil. This willstabilize the tone. -H. B. Morris. -0-

Fig. 4-On our mod-el, parts are held onboard by weavingwires through holes.However, you coulduse flea clips. Toturn on locator, wesimply attach an al-ligator clip to posi-tive battery termi-nal. Switch SI,shown on schematic.would be connectedbetween lead goingto alligator clip andpositive lug on Bl.

Fig. 5-Completed locator. Handle on our model Is6 -in. long to keep hand away from circuit. This pre-vents hand from changing oscillator's frequency.

4

112

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