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EXPERIMERTER

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T H E

HAMMARLUNDSHORT WAVE MANUAL

SIXTH EDITION

CONTENTSIntroduction... 2-3

Two Tube Reeeirer 4-5

QST-Two Tube Superbet 6-7

Two Tube Preselector... 8-9

Three Tube Regenerator 10-11

Receiver Power Supply 12-13

One Tube Transmitter 14-15

Short Wave Components 16-17

815 -Dual Beam Transmitter..... 18-19

Two Tube Transmit ter (812 tube) 20-21

ECO Transmitter of 'Modern Design 22-23-24-25

Medium Power Modulator..26-27Antennas (receiving and transmitting) 28-29

Transmitting Power Supplies ....... ...30-31

PUBLISHEDBY

THE HAMMARLUND MFG. CO. Inc.424 W. 33rd STREET, NEW YORK CITY

Printed in Unitircl States of Ameri-et Fr,rm SWM 610

2 The HAMMARLUND

INTRODUCTIONAMATE[ II RADIO is truly an Ameri-

can hobby, and has proved time aftertime to be of great pithlie value. lriof emergency, amateur stations have car-riers on lllllll uniration long after generalpublic and private fiwilities hail failed.Floods, hurricanes. etc. base all providedtweasions for amatcar radio to performgreat public services.

This book rout

des of simple equipment with which toget started in this fascinating hobby. lie -fore transmitting equipment is used it isIllst.t.SAELry to obtain a government license.The penalty for illegal operation is heavyand since a license is relatively easy toobiain. there is no excuse for 'loot leg-gers.' its they are called by amateurs. Thebeginner will need to study other books.Those to he recommended are faddish:91by the A.R.11.1.. (American Radio RelayLeague). an org %tat if ill composed en-tirely of amateurs.

Now more than ever before a greatmany operators are in demand. Whilethere are some 5004 "ham" operatorsall are not able to serve, and new onesare continually needed to keep pace withour defense program. Training in ama-teur radio is perhaps the greatest as -set a

iirospective commercial or governmentoperator east have.

Amateur radio iif course holds tither at-tractions: e.g.. alnateura llllll unicatew ills ex peili 1 ion% a id provide regular sched-ules for members to communicate withfolks at home, Also various groups ofumateurs have established relay violinsand receive arid transmit hundreds of mes-sages each week. Others belong In the

A typical .armyAmateur Net sta-tion, ErAL.NC-114-4NG. This sta-tion was also usedI u revel re IFICS-

sages front mein -hers of the Byrd

Expedition.

ArmyAmateur organize Lion wit ill) is alliii-ated with the United States Signal Corps.There are hundreds of other interestingangles to amateur radio and first amongthese, is building and experimentisig withyour own transmitters and receivers. Whilemany Thanis- use factory made transmit-ters and receivere, the majority build anddevelop their owti equipment from partsavailable through authorized amateur sup-ply dealers. The budding amateur usuallystarts off with building a simple receiver.

These simple receiving sets are reallyline performers and it is not too manyyears ago when they were used in nearlyevery Their perforillUnreof course, cannot be compared with thatof modern ei llllllll mications receivers, butnever -the -less they di get signals from allparts of the world under favorable (.011-

SHORT WAVE MANUAL 3

Fanto US "Super -Pro" receiver wellknown to ama-teurs and corn -m erc ia I oper-ators. Receiverssuch us this neare used exclusirely in commer-cial services. Sea --era were em-ployed an theByrd Expeditionto the Antarctic.

di bons. Interference a the great bug -a -boo, with the simple regenerators. Super-heterodyne receivers on the other hand,operate on the principle where selectivityis independent of the operating frequencyto which the receiver is tuned. Small re-generative receivers must have all circuitstuned to the signal frequency and conse-quently the selectivity varies considerably.An ideal receiver would be one havingvariable selectivity characteristics of quitea wide range. The Hamtnarland "Super -Pro" is an excellent example of such a re-ceiver. It. has a band width front nearly16 he. to better than 100 cycles. Thispermits reception of high quality musicunder suitable conditions arid also makes

Mrs. Clay Bailey,wife of the chiefradio officer of theByrd Expedition,listening to broad-casts erninntingfrom the South.Pole. The receiveris an "HQ -120-X".

available any other degree of selectivitywhich might be required. For generalshort wave reception in crowded amateurand broadcast bands, a high degree ofselectivity is more to be preferred, thanthe wide hand type of seleetivily. Hereto. there is great advantage in having thevariable feature. The Hamrnarlund -HQ--MA" has a variable range of selectivityfrom 100 cycles to over 3 ke. This takesin practically all short wave broadcast andamateur requirements.

'i're gel the most Out of any receiver,regardless of whether it is a simple regen-erator or a complicated communicationstype receiver, the operator must spend agm! 1 many 1 , :it she rontrols.

4 The HAMMARLUND

ISN4 ago "PlililgelanMml....1061121

Rear and bottom i'letr9 !atoning placerneril of parts and wirin,q.

The "Metal Tube Two"THE `"Metal Tube -Two" receiver is for

the more advanced short wave experi-menter. Two of the newer nietal tithes areemployed. One is a 637 regenerative de-tector and the other, a 6C5 triode, is aresistance coupled audio amplifier. Thisimmbination provides about the Elli I e

in simple short wave receivers. It is espe-daily sensitive and will produce extremelyloud signals. Loud enough, in fact, tooperate a small speaker.

This receiver is designed to operatefrom the power supply described in an-other part of Ibis hook. Two -hundred -fiftyvolts are required for the Ii -supply arid6.3 volts A.C. for the heaters.

As in other receivers previously de-scribed, we also employ standard Ham-marlund SWE, plug-in coils in this one.In simple receivers the plug-in coil methodis unquestionably the most satisfactory,because there is no danger of dead spotsdue to absorption caused by unused wind-ings. here trio, we have also employedthe hand -spread system shown in theother receivers.

The tickler is connected in the platecircuit for obtaining regeneration. In thediagram, the tickler is shown al the topof !he grid roil while actually it is wound atthe bottom of the coil form. However.the connections remain identical. It isdrawn at the top merely as a convenience.

In order to eliminate feed back in theaudio stage, and to keep all traces of

nut of the grid circuit of the audioamplifier. a filter consisting of a 2.1 colt.R.F. choke and two .1.1005 mf. condensers,is employed in the B -plus side of thetickler circuit.

Regeneration is controlled by varyingthe voltage applied to the screen grid ofthe fi.17 regenerative pentode detector.The 50,000 ohm poieritiometer and the100.000 ohm resistor, arc connected inseries across the 11 -supply, that is, he -I een the 11 -phis and It -negative, in orderto Oh t a in the correct vidtage for the screengrid. The adjustment of this regenerationcontrol is covered in other parts of thisManual and need not be discussed here.

The 30 Inn& trimmer, connected inseries with the antenna, serves for vary-ing the antenna coupling. Once set forthe highest frequency coil, this condenserwill need nn further adinstment unless anextremely weak signal is encountered.Closing the condenser plates (increasingcapacity), will increase the sensitivity andthus bring op the sirength of the weaksignal. However, as the capacity of thiscondenser is increased, the set antomati-eally tunes broader. There is an optimumadjustment; one which provides sufficientsignal strength without interference fromstations transmitting on adjacent channels.

SHORT WAVE MANUAL 5

elimerisionN for chosNin.

The diagram contains the circuit foran athlit I pentode power amplifier.This amplifier. when added to the mainreceiver will provide full speaker v it! URICon all popular short wave stations. The.006 Inf. condenser connected betweenthe plate of the 6(3 and the II -minusshould lie connected between the plateof the 1W6 and B -minus when the addi-tional audio stage is employed. The partshat does not contain the iienis emphoyedin the additinnal amplifier. Also, thechassis un which the original receiver isbuilt is not large enough for the secondamplifier. We suggest a l0" chassis oneextending 2" farther to the right. Thedrilling of tile r portion will, of course,remain the same. The panel should alsobe correspondingly larger.

This receiver has been found to operatehest on an antenna from 40 to 75 feetlong. Consisting of a single wire, theantenna should he mounted in the clear

and away from all trees, metal roofs, etc.A receiver is only as good as the antennawith whirl, it is used. Il.se a good antennasystem anal you will be well repaid.

The beginner will find this the ideal setwith which to start. Even today thou.sands are in use by llama.

P.1RTS LISTHAMMARLUND

I- MC.140.M Rand setting cond.1-MC20-S Band -spread cond.I -MEX antenna trimmer 130 masc./1--C11X r.f. choke1-S-4 socket2-S-8 sockets1-SNICK-4. 17 to 270 meter plat[ -in coil

setCORNELL DORMER

1-100 mint. mica condenser2-500 mmf. mica condensers1-.006 mf. mica condenser1-.1 mf. paper condenser2-1 mf. paper condensers

I. R. C.

1-2 mete. t 2 watt Resistors2-1/4 meg. 1/2 watt Resistors1-2,000 ohm 1 watt Resistor1-100,000 ohm 1 watt Resistor-50,000 ohm potentiometer

MISC.

1-8 a 5 a 2" Chassis1-8 x 6 a 1/16" Panel (aluminum/

Terminal strips, screws, etc.

C. A.

1-6J7 metal tube1--6Ci metal tube

St .?$01. OPTIONAL PENTODE AMPLIFIER

Wiring diagram for Weird Tithe Two-

; The HAMMAFILUND

QST2 -Tube

SuperhetWHILE this rs. loperalet Ott the

superliercri.i, ,i, principle. the be -inner will penbahl:. get a clearer picture

of the circuit by considering it a modifiedregenerative type receiver. In a regener-ative receiver the detector is tuned to theincoming signal. The disadvantage lie. inthe fact that the frequency of the detectormust be changed to coincide with the fre-quency of the desired signal. If w, couldhave all sipials ulcerating sin Idle &el Illerleywithout interference, the detector couls1then be adjusted for maxi ]]]]] /is stabilityand sensitivity. The ...kik..., ',ohs( iscenisto he to convert the frequency of the de-sired signal to that of the regenerative de-tector which in liked tuned: that is exactlywhat is done in this receiver. A eirawerierstage operates ahead of the regenerative.dereetio. The regenerative detector oper-ates exartly the mouse as in other receivers.except that its frespicury rensains Citedafter it has been adjusted for maximumperformain.e. "Ile same thing happens ina superhet, except dual an IF amplifierusually exists between the non ert tiy titNi the second iletertor.

By selecting a rather high frequency atwhich to operate the regenerative detectorin this receiver. it is possible to reduce theshortesiniings of the usual simple Super -

This two -tube Naperhetniodeled of ter fire-r' sivilyseribril in "ON 7'magazine. ,Warty buddingamateurs will do well tostart out with this type

of receiver.

heterodyne toll having preselem ion. Someinterference from images will he presentbut it is obvious that this receiver shouldoutperform a usual 2 -tube regenerator.The irlier-raerlialr frequency in this par-ticular ease is approximately 1600 lite. Theconverter system consists of a 6K8 in theusual iwistagrill circuit. The second de-tector Drill nadirs amplifier are cosithined ina twin triode bElit;. The chassis on whirlsthe receiver is no milted is 5 x 9 x I I..,"and pro% isles ill milk. space fsw all parts. Thephotographs dearly illustrate the /111,11.cif die vele-- arid condensers. I of

2: r.sraa

Wass.

Va'Yi0W-ND 4.;

-"AV

t. I pm.. 4 Pica_Es

ti-11SX.1.3 KM P.

Eelnr-V

toy-intr./or fr41 trrlsrrcreperlret.

SHORT WAVE MANUAL

a metal chassis in this receiver togetherwith the superheterodyne type of circuitcompletely eliminates hand capacity ef-fects. This alone is quite an advantageover the usual regenerator. The second de-tector tube circuit is wound on a clearplastic form 1,-4" in diameter and consistsof 55 turns of No. 30 double silk, coveredwire close -wound in the grid coil LS, and 18turns close -wound for the tickler L6. Thesparing between the coils is approximately1/16 of an inch. Winding data for the con-verter coils is given in the accompaningtable. Results obtained with this receiverdepend largely rm the performance of theregenerative second detector. Adjustmentof the feed -back condenser is iminwtani forcode reception. I t should be adjusted tothe point where the detector oscillates andfor reception of modulated signals it shouldhe adjusted to the point just before thedetector goes into oscillation. It will befound that this control will need no atten-tion after it is properly adjusted and thatis one of the great advantages of this typeof receiver. In the usual regenerative re-ceiver, it is necessary to readjust the re-generation control when tuning. Then too,dead spots caused by the antenna ure en-tirely absent in the receiver.

Coil DataCoil Grid Winding (Li and L5A 56 turns No. 22 enamelledB 32 turns No. 22 enamelledC 18 turns No. 22 enamelledD 12 turns No. 22 enamelledE 10 turns No. 22 enamelledAntenna 112) or Tickler (1_41

A 10 turns No. 24 enamelledB 8 turns No. 24 enamelledC 7 turns No. 24 enamelledD 7 turns No. 24 enamelledE 8 turns No. 24 enamelled

All coils wound on 11/2 -inch diameter formsCHarnmarlund SWF-41. Grid windings on coils B -E,Inc. spaced to occupy a length of 11/2 inched; grid wind -

Wiring diagram of2 tube Superhetero-dvne. Each tufwdoesthe work of twotubes. .4ct ually,fortrtube performance is

obtaned.

flnrrum reerr- two re 44- picreenterri ofparts.

Eng on coil A close -wound. Antenna -ticker coils allclose -wound, spaced v. inch from bottom of gridwinding.

Frequency Range Coil at L1 -L5 Coil at 1.3. -Lo1700 to 3200 kc.3000 to 5700 kc..5400 to 10,000 kc...9500 to 14,500 kc..

AaC

BC

PARTS LISTC4, Cs. 01-100-mmfd. variable (Harnmar-

lund SM-100)C4-15-mmfd. variable (Hammarlund

SM-15)Ca-250-mmfd. silvered mica (Dubilier

Type 5-RiCo -0.01 mmfd. paperCr-0.005 mfd. mica.Cs-Cs 100 mmfd. mica.Ki-50,000 ohms, 1 /2 -wattRs -1 megohm, 1/2 watt.RFC-2.5-mh. r.f. chokeTi-Audio transformer. interetage type.

3:t ratio (rhordarson T 1 3 A 34)Li, Li, inc.-See coil cable

turns No. 30 d.s.c. close -woundon 3/4 -inch diameter form; inductance40 microhenrys.

L.- 8 turns No. 30 d.s.c close -wound, onsame form as La; see Figure 2

S-S.p.s.c. toggle switch

8 The H A MM AR LUND

Front and rear views of the 'TiroStage Pre -Selector." Ide.rai unit for re-ducing noise and images.

J

Two Stagerrifi.: pre -selector is ii worthwhile uddi-

tiun to any superheterodyne, particu-larly those not having too much sensi-tivity. This one, in particular. will workwell with present superlieterodynes havingno B.l. ahead of the first detector. Eventhose already having one stage of H.F.can he improved by the use of this unit.Not only does it increase the sensitivityof your present superheterodyne, but italso goes a long way toward eliminatingimages- that it, two -spot liming. Noiseis also reduced somewhat due to the ',venalincrease in sensitivity and selectivity ofthe receiver.

A power supply for operating this pre-amplifier is not included in the unit.Inasmuch as it is to be used with somesort of receiver. the lower can be takendirectly from the receiver power supply.From 180 to 250 volts are required forthe plate supply and 6.3 volts for thehealers. If your preseiti receiver emplity132.5 volt tubes. such as the 38's and Sh's,then it will be necessary to employ twotype 58 pentodes in place of the 610metal tubes shown in the diagram. Ifthe glass tubes are Itsed, it is necessaryto shield them in order to prevent feed-back. In this regard. the metal tubes aresuperior because of their thoroughshielding.

It will he noticed that the two plug-in coils, VI:laid! are SWK-6, 3 -windingHammarlimil coils, ar' shielded withHaminarlund "'CS- coil shields. Do not

This unit trill improreany superheterodyne

Pre - Selector:Attempt it, operate the amplilier withoutthese shields because it just won't work.Also it will be noticed that the dual I tOmud. condenser has a shield plate he-tWeerl 1110 11111 stators. This must alsobe grounded in order t eliminate feed -hack.

Band spread is not employed for thesimple reason that it is not necessary.H. F. stages tune rather broad as com-pared to the, tuning control of the re-ceiver. In the first H. F. stage-that is,the one nearest the antenna circuit, theinterwound winding is employed for trim-ming. 1 here we have a ItOtt minf. con-denser oinneeied across the winding withone side grounded. The grounded side isthat nearest the grounded side of the

lir ...AFL_ ior

Bottom rime showing the wiring.

SHORT WAVE MANUAL 9

L

21-*1DRILL Fit 26112 HOLES .

( N

C01

DIA.4 Hp LEs

7 MCDI MC 140-M r

F &ONR100-51 r a

11 II

Wr.

Drilling dimensions for the chassis.

larger winding. The small coil at thebottom of the form, usually termed thetickler, is used as the antenna couplingcoil. Thi6 dril remains 111111141,d 111 thesecond stage. The interwound windingserves as the plate coupling coil and thelarge winding as the grid coil for thesecond amplifier tube. This also is tunedwith a 1.40 mint condenser. With properadjustment, of the 100 mmf. paddingcondenser, the two circuits will track verynicely.

There arc many arrangements whichcan he used for coupling the pre -selectorto the receiver proper. Ifowever, thearrangement shown is the simplest andis entirely satisfactory. Merely connectthe output tenninal of the converter tothe antenna post your receiver. Thenegative side of the converter need nutbe connected to the receiver because thisconnection .is already made through thepower supply. In wiring up the converter,all leads should be short and direct.

Long leads in a high gain amplifier ofthis type will cause no end of trouble.The longest lead is Ilse one. going fromIlse second coil to the plate of the first610. It will be noticed that this leadis shielded in order to reduce feedback.Do not employ ordinary shielded wire.This lead should he made with hook-upwire having heavy insulation, and a shortlength of braided shielding material shouldbe played over the wire. I f th., capacitybetween the shielded wire is too great,considerable sensitivity will be lost. Theconverter has a volume control of itsown which should be operated independ-ent of the receiver. The correct settingfor the volume control can only he learnedhr experience.

PARTS LISTIIAMMARLUND

1.-MCD.L.40-M two gang condenser1-MC-100-M trimmer condenser1-CHX R.E. choke2-S-13 sockets2-5-6 sockets2-CS coil shields2-SW14.6 6 -prong coil sets 17-270 M.

CORNELL DUBILIER(Condensers/

6-.1 mt. paper1-500 rural mica

I. R. C.Resittors)

2-300 ohm 1/2 watt2-10(4000 ohm 1/2 wart1-50.000 ohm 1 WALE

1-10.000 ohm PO1CM1011MI141Se.

-8 x 10 x 2" chassis1-7 x 10" panel (aluminum)1-Dial2-Knobs

Binding post strips, screws, etc.H. C. A.

2-6K7 Merar rubes

Wiring diagram and ratart+ "Tarn Singe Pre-sehalor...

10 The HAMMARLUND

Three Tube Regenerator

Three tube receiver for the beginner.

911-11-S simple three tube receiver eta -ploys an untuned RF stage. The pur-

pose of this RF stage is to reduce detuningeffects, usually caused when the antennais directly coupled to a regenerative de-tector grid circuit. The RF tube operat-ing with relatively fixed characteristicsprovides a uniform load for the detectorcircuit and also isolates it from the an-tenna.

Radiation from the oscillating detectoris also reduced. An oscillating detectorcoupled directly to an antenna works muchthe same as a transmitter and will inter-fere with other receivers tuned to the samesignal. The addition of the RF stage how-ever, prevents such radiation. Regenera-tion is also less difficult to control when theantenna is not coupled directly to thedetector. This is due to the relativelyconstant load, as pointed out previously.which exists with the additional couplingstage.

Dead spots usually caused by rem -maulcharacteristics of the antenna also do notappear in this receiver. The regenerationcontrol is not at all critical and a singleadjustment will suffice over a relativelywide band of frequencies.

$tandard 3 -winding Hammarlund coilsare used in the tune circuit. The primaryor plate coil for the R F tube is interwoundwith the detector grid coil. The usualplate tickler, or feedback coil, is connectedin the cathode circuit. The normal ticklerwinding with which these coils are wound

is too large fur use in a cathode feedbackoscillator and therefore, requires pruning.We have found that approximately 12 theoriginal number of turns works out satis-factorily. Additional experimenting mayhe required in individual receivers.

Single -ended tubes are employed be-cause they definitely make the wiring jobeasier, although if the experimenter hasother tubes available, there is no reasonwhy they should not he used. The audio

Inside view

SHORT WAVE MANUAL 11

PARTS LISTHAMMARLUND

2-CHX choke1-set 17-270 meter coils, SWK-61-50 minf. var. rood. IAA -50-B1-100 mrrif. %sr. cond. 1-/FA100.A1-6 prong socket, S-63-8 prop _F socket, S-8

CORNELL Milli LlER6-.05 mi. paper cond. 500 V3-.0005 mf. mica Eland.1-.0001 nif. mica cond.

1. R. C.1-300 ohm 1.2 resistor1-100.000 1;2 resistor1-2 meg. 1 i 2 resistor3-1/4 men. 1/2 resistor1-2000 112 resistor1-000 112 lOW resistor1-20.000 ohm pot.1-50.000 ohm resistor

PAR METALI-7' a 7" a 2' chassis1-cabinet to march

R. C. A.1.-6C5 tube1-6SK7 tube1.-6S.17 tube

MLSC.1-pilot light a sse=7,

stage is a triode and providtt, sufficientvolume for earphones. A pentode mighthave been used hot the increase in volumewould not have been sufficient In niscra tespeaker and for earphone operation therewould have 'men no particular advantage.

Power for this receiver may he obtainedfrom the supply described on pagm 12 and13. Any good power supply however, de-livering in the neighborhood of 200 to 250volts. will servo nicely.

Operation of the receiver is much likeother regenerative receivers. In additionto the regeneration control there is also anHf gain control. Actually this should betermed an aIIcnlratlir fur 1Iiire 1111

notiont view sl ins re.sislors am!condensers.

in the untuned HY stage used in this re-ceiver. This control reduces the strengthof strong signals which would overload theregenerative detector. Sisece a regenera-tive detector works best with relativelyweak signals, this control is definitelyworthwhile. F. very strong signalssuch as local broadcasting star willcause interference in this type of receiverand it is advisable to use a short antennato limit this irturference.

In addition to controls already men-tioned, there are two tuning condensers.One is termed "main tuning.' and theother "hand spread''.. The main lottingcontrol adjusts the receiver to the approx-imate freapiency or hand of frequencieswhere reception is desired. Fine tuning isthen done with the hand spread coorrol.

300OHMS

r/2 W.

EISK7

V20,000OHMS 8-1-

2 MEG. 69J7

.05 Mr.

50.000 OHMS1 W-

100.000 OHMS. w

6J5

10 -MF.

(1

5.

.25m CO,y, w.

1

ZC

If Irirrg diog r .for 3-tufer

12 The HAMMARLUND

ReceiverPower-

Supply

Two riewa show-ing the et-m.0rue-tionof the reeeirer

power -supply.

rr Ill. several short wave reeeivers pre -v. ly described require a separate

power -supply. While the power -supply andthe receiver may be incorporated in oneunit, it is to the advantage of the experi-menter to have the power -supply separate.This permits its rise with other apparatus.This power.supply is einihtrueted of goodparts with ratings sufficient to work withthe res'rivers in this hook and still main-tain a wide range of safety. If the experi-menter desires to build larger receivers,that is, receivers having considerably moretubes than those illustrated in this hook,it is advisable to use cottoottents of higherratings. For instance. the power trans-former in this particular lamer -supply,while delivering sufficient voltage at 79milliamperes, will handle up to three orfour tubes. In case larger receivers areto be used with it, we rev nil thatthe transforelier have a rating of at least100 milliamperes. The filter choke coilsof this power -supply are rested at 1311 ma.These also sl Id he inereased fa approxl.maidy 109 11111, if the larger sets are con.teniplated. No other values in the powersupply nerd be changed in order to in-crease its current capacity. Another poini

which should be ianisidered is the istithes which eta) at some time oir 1.11/1Cr

he used during experimenting. Our dia-gram shows a single 6.3 volt filamentwinding. If at any -time you expect toemploy volt tubes in your receiverfor some other experimental set -op, wesuggest that the power -supply be equippedwith a V? volt winding as well as the6.3 volt winding. Such transformers arereadily available. For convenience, wehave mail a ixflx2 inch chassis constructedof f. IC al ' . Ail four sides arebent down in order to make it rigid. Onone of these sides is mounted the terminalstrip containing die plate and filamentconucetimis. Oil the uthrr sidr we. havethe on -off toggle switch. The placementof these items can be learned from thephotograph.

The output voltage of the 'lower -supplyis very important. In this parlieular tine,the mil put voltage is 300 under normalload. Choke input is employed. If con-denser input were used. the voltage wouldbe entirel ton high. If condenser inputis desired. for any particular reason. thehigh voltage rating of theseelalllrry shouldlie around 2511 villa. The Illeioler sir sniragr

SHORT WAViE MANUAL 13

divider ei.inai'Zted fleellbS the output ter-minals of the filter consists of a 20.000ohm 50 watt resistor. As ran beAcre in the diagram, tole tap is providedin ease lower voltages arc required. Thislap should he adjusted under load withthe aid of a voltmeter in order to obtainproper voltage. if inure than one inter-mediate voltage is required, additionallaps may be placed on the voltage divider.However, bear in mind that the resistorslinem is only rated al 50 watts and that(here is an idle current of approximately15 milliamperes already flowing ilirongliit with no load. This means that theiota' additional load %bleb the resistorwill tam]. is 35 ma. If greater currentrequirements are necessary a resistor witha higher rating should lir employed. Oneid approximately 75 1n 100 watts wouldserve, depending upon the current drawn.[luring tests, this power -supply in ciiri-junction with iiir rersiiVerA lirelii011114- il-lustrated, was what might be consideredhunt -free. If trouble is experienced clueto tunable hums, that is, I a appearingin s places tm the dial in the receiverand suit in others, they may be eliminatedby connecting .001 nif. condensers lie -

Wiring diagramand purls valuesfor power-214113ply.

Drilling specifica-tions for power -supply chassis.

tween each plate of the rectifier and oneaide of the filament. Juggling these con-nections may be necessary in larder tocompletely eliminate tunable holm,. Also,outside line noses can be reduced con-siderably by romierting a .1 inf. con-denser between one side of dye l II

primary and B -minus. Use a high grade1A/0 V. paper r leaser.

PARTS LISTSTANCOR

1.-Power transformer-P 9482-Filter chokes-C-1420

AEROVOX3-8 mt. elettrolytic condensers

/S00 vp.C

1-20,000 ohm voltage divider with oneslider

R. C. A.L-Type Sit rectifier

MSC1-5' s ir x r chassis

/1;16* aluminum/1-Taaale switch

14 The HAMMARLUND

This earn tube trans-mitter is ideal for thebeginner. his effectireand amateurs hareworked stationsail orerthe trpriii with this type

transmitter.

1 -TUBE BEGINNER'STRANSMITTER

0 \F. noa hovel a list lif IIIIPILI.Vget started in amateur radii,. All

that is neressai-v is a conscientious desireto be a Ilarei and the ability to one'shands.

We assume the reader alreasl, hasAnnie kind of receiver suitable fur opera-tion in the amateur bench;. Many pimpleruceicr, arc described in this, and silliermagazines. We also assume the reader(if he contemplates building 1141 trans-mitter) already has a license or willobtain one before lie attempts to use atransmitter. The simplest form of trans-mitter is the one tube id -let which iscrystal controlled and operates on twobands with a bingle crystal. There its

nothing home-made about this transmitter.Every part is available through your favor-ite item parts dealer. A few of the partscould be made at home but if you are anewcomer, it's safe to bet you don't havea lot of junk nr paraphernalia from whirhyou would be able to snake lite parts iswe were to provide auffieiroi iriformnlinn.

parts are available atid, low rives and, oriillr5E4 Lo say, they

arc superior ts, any even the most experi-enced Ham might build.

The chassis is a 7" x a 2" steel unitwith black crackle finish. A wood basecould be used here. but the few cents savedwould be of little importance. The tubeis a 6I.6 metal type, not the glass variety.In the cathode, we find a standard singlecircuit tuning 'nit which is intended totime in 411 no-iirA, W e have connected anadditional fig l condenser across it, sothat it will lmu. slightly lower in frequencyand enable the crystal to oscillate. In theplate circuit, we have standard plug-inroils and tuning condensers. This circuitmay be tuned to either the crystal fre-quency which is between 35(N) Lc. and36.50 ke..; or to the second harmonic whichfails between 79011 and 73011 kc. (the 48meter band). When the piale, or outputcircuit is tuned to the crystal frequency,the cathode. coil should he shortcircuitedby the switch km' "SX''. Under some

SHORT WAVE MANUAL 15

1kttorn view showing the placementsof Armlets.

conditions, using a tube with hurter in-ternal shielding, the cathode couldlie left operating. We mention this so thatthe reader will not be confused by informa-tion in other articles where this cireuii isleft in operation. With the Us% however,this Cireail 11110111d he shorted to protectthe crystal when the output rireitit istuned to the fundamental. Tuning andadjusting should he done at a reduced volt-age. Use 250 ',Joins or less, or Canner! alarge. resistor, 10,tH110 ohms 25 watts, inseries with the I3 -plus to the plate andscreen. Set the plate condenser at mid-get& and adjust the cathode tuning con-denser for maximum plate mirrent. Then,adjust the plate condenser for minimumtorrent. This indicates resonance. Youran now apply the Full plate and ferret,voltage and connect the antenna. Fur

There are fewparts in this sim-ple transmitterand the beginnershould hare littledifficulty in get-ting it working.

hest all-around results, 1.111e a 11011blei withtwisted pair feeders. If a good grade oftwisted pair is used, this antenna perforinsexcellently and is very simple. l i will.however, only work on one band. The-finale wire fed Hertz will work on a andIll meters with fair Mirotas, but is slightlymore complicated. In either ease, afterthe antenna is connected. the plate circuitshould he retuned for the lowest plate cur-rent. If this valve is itnintl to he till§increase the antenna emipling. This earslie actmanplished by winding the antennaaril on top of the plate roil near the. B -plusend. In this ease, muse wire wills good in-sulation. In the ease of the Hertz an-tenna, increased coupling is accomplishedby moving the tap nearer the plate end ofthe output coil.

PARTS LISTHAMM AR II IND

1-40 meter coil. No. 421-80 meter roil. NO. 431.-MC-100-5 eerie* condenser1.-ETLI-40 [anion unit1-X5.2 crystal socket1-S.8 rube socket1-5.4 coil writes1-a -IX R. F. choke

I. R. C.t-400 ohm 20 wart resistor1-20.000 ohm 1 watt resistor1-20.000 ohm 2 watt resistor

131.11..re

L-3.5 MC. costalR. C. A.

1-616 tubePAR AIFTAL

x:2' black chassisCORNELL DIMMER

1-.0001 ml. mica condenser3-.05 ml. 500 V. paper condensers1-.005' SOO V. mica condensers

01Mr.

..11

.01MF

24,000 OHMS2 W.

16 The HAMMARLUND SHORT WAVE MANUAL 17

Parts for building receivers andtra nsru iI ten; in this hoot., are here

tinted.

CODE

31C -20-SMC 85.24MC-sa-sMC.50-51MC. -75-SMC -75-MMC -100.5MC -100-MMC -140-14MC -140-MMC -200-M

"MC" MIDGETCONDENSERS

Ideal variables for ultra -short aridshort wave tuning, Isolantite in-sulation. All contacts riveted orsoldered. Vibration proof. Newimproved IlanainarIund split typerear bearing. tool noiiisile,a miningcontact. Cadmium plated solderedbraes plates. Shaft -y.

CAPACITY LIST20 mmf. 81.4035 mmf. 1.5050 and. 1.110541 mint. 1.60SO ninif. 2.0050 mmf. .......... .. , . , .. 4.00

100 mmf ........... ....... 2.25IOU mmf 2.25140 mmf.,...... .. ..... 2.50140 2.50200 mud. 2.75260 mmf. 0.00

mr-125..m 320 rend..,......... ... .. .. 3.50M"-Midline Pleb, -S"-Straight Line Cap. Plates

"MCD" SPLIT -STATORCONDENSERS

Like single midgets, these incor-,rprirate every requirement im-

perative to highast quality. Speci-fications identical to single typesexcept that shield plate is locatedbetween skim stadiums. Overalllength behind panel -.3%.. Strongholentite hese. Single hole panelmount.(NIDE CAPACITYNICD 50 MMCD-50-nMC11-100.SMCD-100-MNI CD-1.44)-31

140-$

'M"-lfilidline Plates

50 eimf. per we.50 mmf. per sect..

WO mod. per sect.100 mini. per sect..140 mmf. per seeL140 mint. per sect. . 4.1W

'S" -Straight Lute Cap. Plates

ttsT...83.00

3.003.503.504.00

"MODS" DOUBLE SPACED CONDENSERSLIST

MCD-33-SX 31 mid. per sea. -63.511MCI).38-MX 31 niter, per sea.. 3.511"M X "-Miillion Plates "SX"-Strsight 1,iric (*an, Plates

"HP" MICRO

ONDENSERS

For tuning or trimming on highfrequencies. enimintn plated sol-dered plates. Isolnidite.Base mounting, single hole panelmount, or panel mantling withhushing.. 110 mint. size 1 0;32"high x 7/32" behind panel.HF-15 1.7.5 mud. ..... ..$1.25/1E45 35 tend 1.50HF-50 50 rumf 1.60HF-I0f1 100 mm(..... 1.00ITF-140 140 mmf 2.25

HF-30-1 30 . 1.85Dotable-Spared

HAMMARLUnDHAMMARLUND MANUFACTURING CO., Inc., 424-438 West 33rdjStreet, New York

"IIFD" mt(:Rt) DUAL CONDENSERS

A compact dual -ideal as ahigh frequency tuning COD,

denser. for tuning low -pow -erect short wave rind enlre-bnrl transmitters.

etc.. Heavy Isolantlite baseequipped with new HIM.marbled split rear bearing

and individual noiseless wiping contact for each sect' . RotorContacts variable Is, several p01;14011,1 for shortest leads. Shieldbetween sections. The 140 come. sue is 1t.i" high x longbehind panel. ?-4" shaft. Cadmium plated soldered brass plater.

CODEquw-so 00 mmf. per sect. . ... .62.75HFD-100 100 rind. per sect. , .... 3.25IND-140 140 :unit, per sect..... . 3.75

HFO-341-X 26.5 mint. per sect, 3.25Itouble-Spaced

CAPACITY LIST

"SM" M II)(;ET CONDENSERSFor receiving and transmitting,for short wave tuning. regenera-tion. antenna coupling. etc. Lowloss, motived hakelite insulation.NOR-e011ThilVe 111111T1111U111 plutes.Phosphor hrnere spring plate af-fords proper tension and smoothcontrol and provides perfect con-tact. Singly Jude mounting. Ba"shun. 5/16" tutinnting bushiest.1 9/15" wide x high. Depthbehind panel from 11,14" to 1176.depending on capacity. Light in weight. strong and compactin construction. Tinned soldered legs on the front end urnsupplies! to simplify wiring. Plates of straight line earineitytypes.CODEtill -15SM-25SM -50S31-100SM-140

"SM-35-X'SM-6a1

C IPAC1TY LIST1 h mud.. 8.5525 mud. .0550 mmf. . - . . ,141

100 romf. . ....... 1.00140 tomb........ 1.2535 nunf... .... 1.0050 mmf t.25

"Double Spaced Transmitting Types

"XP -33" COIL FORMS AND KITSOutstanding forms using new low loss inoils-Linn material -XP -53, Natural coloring elimi-nating losses. Groove -ribbed for air spaced

Flange grips, meter indexes.Moulded t hreaded shelf in form. 13-j" diameterand 27A" long exclusive of prongs Kits withwound coils for 111C. -141.M condenser alsoavailable.(088 LISTSWF-4 (4 prongs, evil form only ..SW P-5 (3 {wino, coil form 01:0y1.4WE-6 (6 -prongs, led form only). .

No. 40 coil iwound coil. 4 prongs, 111-20 meters) .

No. 4l coil (wound coil, 4 prongs. 17.41 meters)No. 42 coil remind coil. 4 prongs. 33-75 meterii..No. 43 coil .1 woutul roil, 4 prongs. 66.150 meters) .....No. 44 roil remind end, 4 prongs, 1R.5-270BC(' -4 (wound roil. 4 prongs. 250.560 meters) .

No. 60 coil (wound coil, 6 prongs, 10-20 meters).No. 61 coil (wound coil. 6 prongs. 17-41 meters .....No. 52 coil (wound coil, 0 prongs. 33-75 meters)...

8.34.35,411

1.0111.001.00.75.751 II1.251.251,25

No. 63 roil (wound coil Riz-prangs,1111-111)) meter) .. , . 81.00No, 64 coil (wand roil, sie-prongs, 135-270 meters) ... .. , 1.00BCC -6 (wound coil, 6 -prongs. 250-560 meters) . 1.50SWE-4 (kit -4. four -prong coils. 17-270 meters) 3.00SWE-6 (kit -I, six -prong soil, 17-270 meter. , ... . 3.75

"S" ISOLANTITE SOCK Ers

Standard socket at left. Lewmta.',,nssiss, losses. Constant resistivity.Gripped prompe--cannot shift.:lode groove, Rinit-proof side

....ripping canteen'. (dazed topand sides% Sub -panel or basemounting. 21,{" x 14N",

CODE 1.15'1'

!4-4 prongs', 6010S-5 prongs) .1111

ei..6 6 prongs)flge. base. 7 prongs .. 80A (sm. base. 7 prongsi... 40

prongs) .75Aorta socket at right. Isolantite.Pot new high frequeney acorntuhoi-954 or 955. 1- dia-meter. Five loupe grip silverpianist phosphor bronze prongs.Fop, silirg, amt plug iris:evil.

U115-900eniW LIS1'

NEUTRALIZINGCONDENSERS

Improved metre's:dug romicuser,with heavy aluminum' polishedplates and rounded edges. Isola ,tile. Fine adjusting screw. Perotire licking nut. 'Designed forherizontal adjustment.high x 1 13116 deep.CODE LISTN -t0 '2 to 10 mmf

I'

EXCITER TUNING UNITS

These exciter tuning omits are available for80,40, 20 and 10 meters. 'They are adjustedso that they will cover the entire bandwhen u.sed with the usual 6L0 ur similar(Ape tribe. The ECO.160 Is red in theelectron eonplerl mscillator described else-where in thus hook. It is designed formaximum stability and should be usedin conjunction with the ETU -SO. When

1411 mid. tutting condenser is used, theentire SO meter hand rim he etsvertsl.

The permeability tune coil rric.-io covers only the 40 meterband aml is dmMtiesi particularly for the type of transmitterdearribed on page 22.

1.15,TPRICE

ETV -80.. ..15.59ETU -40 .5.50ETC- 20 . , 5.501M 10 ...... . ..... 5.50Et '0-1011 12.00

2.00

All prices shown are list prices, and

subject to change without notice.

I "CH-X" R.F. MIDGET CHOKESinvaluable item where space is at a premium. Itis so small in size and light in weight that, it min be

= supported by own leads. /hive impregnated .i it ,

venial retinas' pies .'i'. Impregnated boles-core insuring ruggedness and stability. Ind.= rah. D.C. res.-35 ohms. Dist. cap. -1 mud.Current nevi* cap. -125 ma. Length neruss

(-110 cap. 1W. Diemeter W.('015KCH-230

(2501IA.) 500

11S'1'

"FIFE"INSULATED

ROTORCONDENSERS

This new line of trianunitting condensers departs considerablyfrom the usual design. The end plates me isolanlite /1.011 the.rotor is 100"..; insulated from the mounting brackets. Also, thecontrol shaft in otimpletely insulated from the rotor permittinghigh voltage to he applies' directly to the rotor without dangerof electrieal shock. The length of the condenser varies wallcapacity. The shaft is 115' long and the end OM, oar113/16' square.

CODE

IIFIID-50-ClIFBD-100.0HERD -35- EHERD -65-E

11F11 -50-CFIFA -100-C11F11-150.011E1i-100-E

41A PAC1TYPER SECTION

50100

3565

1(11)

511

I011150100

AmGAP.0.50*_050'.070'.070'.070".050'.050".050".070"

1.11-Pit 111.

84.155.155.507.009.003.203.704.105.11)

IIFA" VARIABLECONDENSERS

The HFA isindenser is available in both the single and dualtypes. The type -A" has .020" plate spacing and type "11"has .030" plate spacing. These are romgedly built with ri1 13/32* x 3 1/32" isolantite end panel. Roth singles and dualshave single hole panel mounting and can also be base mountedwith brackets. The IIFAD has 1 3/8" square front and rearisolantite naiads wills a 1.1/141° shaft extension. Coned ruction isthe same as the 111' It type ronderiser.s. Heavy brass plates aresecurely soldered and the entire assembly is cadmium plated topreserve the finish.

CAPACITY TYPECODE PER SECTION

HEA-75-A 75 mud. singleIRFA-200-A 1041 inns. singleIIEA-110-A 140 mmf. single111FA-25-11 25 mmf. singleHEAD -75-A 75 mmf. dualHEAD -100-A 100 mint dualHFAD-146.A 140 rend. dualUFA 11-25.14 'a eying. dualREAD -100-B ISO mmf. dual

LISTPRIC1

4.00

For complete catalog of Hanuruer-lund parts. write Dept. SWNI-::

address given above.

18 The HAMMARLUND

2 -Tube 815 TransmitterAFTER passing through the beginner

stage, the new -ham" usually requiresgreater flexibility and increased power notfound in the first transmitter. Operatiort1111 several of the amateur 1111111dg its desiredafter lie -newnessa' has worn off and thismeans the seminal transmitter must be ofmore elaborate design. Si nor iii t hr neve it tlydeveloped tubes permit great flexibility insimple designs. The 815, for example. is apush pull beans power tithe which will pro-vide 50 watts output and eau he driven withany small resmiving tube. The oscillator in

wan. N.ZT Cr.LR,IC SPECr.E.0 ry ec wa. 2, MILL

Ilriffirra iiitewrisierns.

ter is a 61'6 connected in a'trite t'' circuit to Alm frepiency multi-plying independent of the amplifier. Theoscillator will furnish excitation on 3 ama-teur hands with one crystal.

The ratlendr. rirenil consists of an ETU -40 tuning unit, in a,irhilion a 100mnd fixedcondenser is externally couneetril acrossIlse coil. Adjustment of the variable con-denser in the t g unit ;Amu at all ethical.

Plug-in roils are used for coupling thetwo stages. The nut primary is lo-cated between the gird coils and the tuningcondenser for ihe grid coil is mounted in-side the coil form. As it Safe,' measure.this coil it shielded to prevent coupling.

The 815 amplifier tube bring easy toshrive requires adjustment of the spacingbetween the coils in order to obtain propergrid current. Appr. ixiina Indy rhisa. providesefficient excitation. With the fully insulatedplate minimiser, the plate voltage can beapplied directly to the rotor withoutdanger of the operator being shocked whenmaking adjustments. This ay.suines, ofCOUrive, that die operator only touches ad-justing knob. Keying can he done in eitherIlse oscillator or amplifier ea desk circuits.When the oscillation is keyed, adjustmentsshould be made while listening, to the signal

SHORT WAVE MANUAL 19

XT AL

r -

6V6

ETU -40

200OHMSI/2 YO,

77`

0REY

7

0

ry

5.3 V.

PLUG-IN COIL, L.---_+_----

rd:

815

20.000OHMS26W.

01 %1F.

L____ ___J g,1i0c

25w. y

tOHMS`

2 w.45V. + 0

- +500V.

0

0

.005M F.

90.0f,CHX

T- -AOC 010siS

2. W.

OuTpu-r

'n a monitor so that the keying will beclean_ Meters can he connected in all cir-cuits, however, a simple and more econom-ical method is shown in the diagram. Herewe find a 100 ohm resistor connected ineach circuit to be metered and a rotaryswitch connects the meter to the olcsiredcircuit. A suitable power supply and modu-lating unit will he found nn pages 26 and 30.

Band20 m.40 m.80 m.

Coil Data, L 1Plate

S

11

Total grid

14:36

Coil Data. L 214 mc, 14 T. No. 167 mc. 24 T. No. 16

3.5 mc. 40 T. No. 18all 2M." Jong, 13/4" dm,

Bottom view show-ing placement ofparts. This t rams-rn itter is easy to build

and operate.

PARTS LISTHAMMARLUND

1.-ETU-40 tuning unit 1-XS-2 Crystal socket1-1-1FBD-1.00-C Var. 1-CEIX RF Choke

Cond. 2-SWF-1-Coil forms1-APC-75 midget cond. 1-CH-250 RF choke2 -8 -prong Sockets, 5-8 1-CS-3 Cnil Shield1-5.prong Socket, 5-5

1. R. C.1- 200 ohms 1/2 w. 1- 6,000 ohms 25 w.1-20,000 ohrn5 1 w. 2- 100 ohms 2 w.1-20,000 ohms 10 w. 1-20,000 ohms 25 w.

CORNELL DUBIL1ER4-.01 mf. paper cond. 600 V,1-.0001 ml. mica Rec. type1-.005 col. mica, 1000 V.

CENTRALAB1-Rotary switch No. 2505

PARMETAL1-7" x 13' x 2" chassisBARKER AND WILLIAMSON

1-80-BVL coil l-20-BLV coil1-40-BVL coil t-BV-hase assembly

R. C. A.t -6V6 tulle

BLILEYI-Variable crystAl

1-815 tube

20 The HAMMARLUND

Efficient 2 -TuberrinE newcomer to ha in radio who chooses1 to build his own transmitter rather

than purchase a ready-made one, usuallystarts off with something simple. T1 gh,all too often the beginner, in his haste toget on the air. puts together a haywiretransmitter with rather disappointing. re-sults. Assuming the beginner is going tooperate nn two hands (80-40 meters) andthe desired power output is in the neigh-borhood of 100 wails, we believe this outfitis just about ideal. Such a rig can be builtcheaply and need not he complicated.

Looking over our manufacturer's tubelist, the 812 variety seems to be the bestbuy front the standpoint of mononty.Since this tube only requires some 5 orft watts driving power for amino] 100 wattsoutput, a single 807 crystal oscillatorshould do the trick nicely. 11. sing the 81)7

in a trite'. oscillator -doubler circuit permitsfull output nit two bands with one crystal.This transmitter works on 80 and 40 meterswills nn provision for adding other bands.Although 20 -meter operation can he hadwith some sadrifire in output, if the final isused as a doubler. In this case, the tubeshould not he loaded as heavily as whenoperated as a straiglo amplifier.

The entire R.F. port' of this trans-mitter is mounted on 71,' x 13" x 2steel chas.sis whirl' was given a coat of graylacquer after all drilling was completed.This treatment provides a notch neaterappearance and eliminates linger stains

Transmitterwhich would appear on the unpaintedchassis.

The cathode circuit of the 807 rsnpLtysa 40.me.ter shielded coil and condicn-wr as-sembly. 'rids unit does not have sufficientrange to tune to a suitable fr....N.1'41- inorder to priVe i de lrculrer cry si .11 ..iwr a t ion.Therefore, it is necessary to add a stuallfixed capacitor of 11)11 mud. In the platecircuit of the oscillator, we have a plug-incoil because here we change front 80 to 40meters when doubling.

The 812 amplifier is extremely simpleand inset the split roil and condenser ar-rangement in order Its obtain neutralizingvoltage. Both stages use a new type ofvariable condenser having an insulatedrotor allowing much more compact eon-8trtietion and results in a considerable sav-ing in cost.

In wiring the transmitter, ordinary »kJpush -hack wire is used and enough terminalstrips are employed to make a neat andsimplified wiring job. The wiring diagramand coil data, should complete theconstructional infix/nation. Getting therig on the air is just about assimple as building it. Apply voltages tothe oscillator and adjust the cathode con-denser for maximum plate current of the807. Then. adjust the plate condenser ofthis same stage for the minimum platecurrent. Neutralizing is next. With fila-ment voltages applied to the 812 but withno plate mirage, open the neutralizing eon.

SHORT WAVE MANUAL 2]

denser all the way. Then, with the meterswitched to the amplifier grid circuit, ro-tate the plate condenser and a decidedchange in grid current Kill he noticed.Swing the plate condenser back anti forth.at the same time close the spacing of theneutralizing condenser. The fluctuationin grid current will gradually becomesmaller and smaller until it disappears. Asthe neutralizing condenser plates becomecloser, the thietnation of grid current willthen reappear. Correct neutralization isthat point at which no fluctuation in gridcurrent is noticed as the amplifier platecircuit is tuned through resonance. Whiledoing this job. it is well to note the pointof resonance, or rather the point where thechange in grid current occurs, and beforethe plate voltage is applied to the 812,the plate condenser should be set as nearas possible to this point. Then, when theplate current is applied, readjust the platecondenser for minimum current.

The last and final operation is connect-ing the antenna to the link coil and in -

COIL DATA50 -meter osc. plate: 37 turns No. 26 bare wire.40 -meter esc. plate: 17 turns No. 22 bare wire.Both coils wound en 4-proung Hammarlund forms

1 t6" dia. and spaced lu a length of 1 va",

PARTS LISTHAMM AR LLT ND

1-ETU-40 coning unit1.-EIEB-50-C (single/ condenser1-11TBD-100-C (split stator/ condenser

Isolantite socket, S prong2-S-4 Isolancite socket, 4 prong1-XS-2 crystal socket1-CH-250 R.F. choke2-CHX RF chokei-N-10 neutralizing condenser2-2-112" stand-off insulators SOS -2501-PTS power tube shield1-No. 43 plug -in -coil for 80 metersi-No. 42 plug -in -coil for 40 meters

Bottom view of two -tube transmitter

crease the coupling until the tube drawsproper plate current. With 1,000 voltsapplied to the tube, the plate currentshould be between 100 and 125 milli-amperes. For highest efficiency, the gridcurrent should be in the neighborhood of25 milliamperes.

BLILEY1-LD-2 crystal (190 meter band)

I. R. C.1-400 ohm wire wound resistor (type AB/1-2,500 ohm wire wound resistor (type

AB/1-20,000 ohm wire wound resistor (type

AB)1-30,000 ohm metallized resistor (2 watt)3-100 ohm metallized resistors (2 watt)

TRIPLETT1-0-L50 milli ammeter

CORNELL DUBILIER1-75 mmf. mica cond. (rec. type/1-.000I mmf. mica cond. (1.000 V)1-.005 mmf. mica cond. (5.000 V/6-.01 mmf. paper cond. (60(1 V. Owar

tiger)CENTRALAB

1-No. 2505 5 -pole 5 -position I sol. switchGENERAL ELECTRIC

1-GL-807 tube 1-GL-812 tubeBARKER-WILLI AMSON

1-BVL Coil base assemblyt-80 BVL 80 -meter coil1-40 BVL 40 -meter coil

ETU -40

Tit GL -1307 C GL -a12

ccx

.CH

* 5 T

0-420Mt.

20,000OHMS

2w.400OHMSits.

NOTE,5 3

aMTOP EWS Or0 0

40 Tier SOCKETS

SHOWN

o o 0 0 6+a C 0 C 4000.

C

3

c -4S 0.

AP. r

15000

Complete wiringdia-gram less power sup-ply. Note the simplemethod employed toswitch the meter to

various circuits.

22 The HAMMARLUND

The performance of au e.c.o.i. at 'ram as much in the con-struction us iii t he cireu i t . Here'sa frequency -control unit whichcoon hi nee a circuit novelty or twowith interesting constructionalfeatures. It has had a thorough"air test" and came throughwith flying colors.

-I compact and businesslike instru-ment haring output on 80, 40, mad20 meters. Complete. includingpower supply, it measures only

by /6 by 8 inches.

A Transmitter Frequency Control Unitwith Three -Band Output

A Self -Contained Cabinet -Type Exciter or Low -Power Transmitter

BY G. W. SMART,* W2.87111N

THE variable -frequency osarilla Ir.r. v. bilenot new by any means. bus reully only

begun In come into its own within the lastyear or tan. We shudder to think of theamateur bands eventually cluttered upwith thousands of e.c.o.'s or v.f.o.'s dart-ing buck and forth like a bunch of sizzlersin an aerial fireworks display; while thev.f.o. is a swell piece of apparatus, it re-quires some careful and prudent use. Un-doubtedly, before the evil of these instru-ments manifests itself, plenty will bewritten to overcome the problem. In themeantime we have found in the v.f.o.something that ran never be replaced byany other instrument. The particular

HammAriund Mfg. Co.. New York City.

v.f.o. to be described is an e.c.o. It seemsthat the type of circuit used is not so im-portant as the physical arrangement andgeneral mechanical design. Before we getinto the details of construction, let's seewhat makes this v.f.o. different from others.

In its design, a definite effort was madeto keep it simple to build and operate.Only one control is operated during normaluse and output is available on three bands-00, 40 and 20 by changing only theoutput coil. Although plug-in coils areused, band -switching could be employedwithout difficulty. Also, the tuned circuitcould be arranged to cover two bands with

one coil so that only two coils wouldbe necessary Int complete coverage.The entire design of this unit is sirn-plified by the use of only a singletuning condenser. Irsuaily three -gangcondensers arc employed in this typeof instrument.

Inside the oscillator tuned circuit assembly.The stiff wires at the corners serve both as

supports and terminals.

The OscillatorThe electron -coupled oscillator op-

erates in the 160 -meter band andcovers 1750 to 2000 kc. The tunedcircuit is a self-contained unit andincludes everything but the mainfrequenty-changing c leaser. Themechanical arrangement of this unitprovides excellent stability and free-

SHORT WAVE MANUAL 23

On the extreme right ran ha- seenthe permeability tuned coil which pro -rides excitation for the output stageOlt 80, 40 and 20 meters. This coil ismounted under the chassis so therewill be no coupling between it and the

output circuit.

darn from frequency changescaused by vibration or shock.This e.c.o. doesn't have to beoperated on sponge rubberpads. As a matter of actualfact, there is only slight mod-ulation, and that from tubeelement vibration, when theinstrument is subjected tomechanical shock. As shownin the photograph four verii-cal bars hold the entireoscillator assembly together,and these also serve as ter-minals for external connec-tions. One goes directly tothe grid of the 6SJ7 tube, a

second to the cathode, one to the B -negativeand the last to the tuning condenser.

Keying in the oscillator circuit is ac-complished by breaking the negative lead.A simple filter consisting of a small r.f.choke and a 0.995-ufd. silvered mica

Lt

O

R1-1 6SJ7a I

C6

TI

S2

'Z CSj,

X

VR-

1

C7

t2ryl

5V4G

X

6.3 V.

65K7a

R

0V.015 TO .s

C13L5

C14

trfsh-crJUNIPERS 1N

REGULATOR TUBE'S

L3Yo

C8 807CAP

C,

L4

C.. - 1- cafd. paper.Ca -35-pil.fd. compensator

(Erie Ceramicon N6801.Ca - 50-ptafd. air trimmer.Ca 3004L ;ad. silvered mica.Ca - 140 -lap -Id. variable (Ham-

marlund MC -140-S).Cf5 - I 00- AiLfd. silvered mica.C7, Cs -5004,14d. silvered mica.Cs - variable (llarn-

marlond MC -LOO -S).Eta - 0.001 -pfd. mica.Ctt-0.005-µfd. silvered mica.C12 - 50-tmlfd. air trimmer.Cia - 8.1sid . electrolytic, 450 -

volt.CI 32-P-fd. electrolytic, 450 -

volt.RI - 20,000 ohms, l -2 -watt.

R - 50,000 ohms, 1 -watt.R3 - 20.000 ohms, I -watt.Rt - 20 ohms, t -watt.R6 20.000 ohms. 2 -watt.Ro -400 ohms. Si -watt.R7 - 400 ohms, 1U -watt.Rs. Rs - 3000 ohms 20 -watt.Li - 30 turns No. 24 enamelled,

close -wound. on ',inchdiameter form. Cathodetap 10 turns from bot-tom. (In HammarlundECO-160 unit.)

L3 -60 turns No. 24 eosin.,close -wound, on 7i -inchdiameter form. 114 andCLa in HammarlundETU 80 unit./

1-3 - 17-pb., 36 turns No. 28,close -wound, on 14 -inch

form, with tuning. Mutt(Hammarlund No.60141.

La 3.5 Mc. -38 turns No. 24,length 1 bf in., diam. 1 i3in.; link I I turns.

7 Mc.-I8 turas No. 20,length 1:4in., diam.in.; link 6 turns.

14 Mc. -9 turns No. 16.length 13.i in., diam. 113in.; link 4 turns.

LS - 15 henrys, 150 -ma_Tt - 300 volts d.c. at 100 ma.,

with rectifier and 6..3 -volt filament windings.

St - S.p.s.t., low -capacity type.Si - S.p.s.t. toggle_Si D.p.d.t. toggle.

24 The HAMMARLUND

denser removes all traces of r.f. andpermits clean keying.

The voltages to the plate and screengrid of the 6SJ7 are regulated, thescreen by a 1.11-105 and the plate bya 11-150. The screen voltage, beinglilt we critical, hat cons' I regulationand consequently a high degree ofvoltage stability is obtained. The 6S17proved to be the best tube for thepurpose since very little output wasrequired. In this particular ease con-necting the screen and suppressor to-gether proved beneficial.

The output of the oscillator is tunedto 3550 kc. with a fixed tank circuit.t nless the entire unit is to be operatedon the high -frequency portion of the80 -meter e.w. band, or the 75 -meter'phone band, Ibis circuit will requireno adjustment. Tuning it to 3550 ke.permits operation over a very wide portionof the e.w. band and all of the 10- and20 -meter hands.

Buffer MultiplierThe second tube in the line-up is a 6.S k

operated as a fixed -tune amplifier -doubler.Its plate circuit is resonated to 7050 ke.with a permeability -Moos' roil. Once set,this eteil requires no adjustment regardlessof the output frequency.

It may seem unsound to tune this circuitto 7050 kc. and expect the amplifier whichfollows to operate in the 3.5 -Me. band. hutthat is exactly what happens. The 807can he operated on the 80 -meter band witheffieiency as great as, if not greater than,that obtained when it is operated on the20 -meter band as a doubler. Sufficient r.f.excitation gets by l..g to snake the amplifierwork effiriently over the r plate 80 -meterband. The 807, of course, is a straightamplifier on 7 Mr.

Output StageThe output of the 807 is relatively con -

slant over any one band and is approxi-mately the same on all three. A carefulcheck of the 807 grid current showed thatample excitation was present at any fee -

Fig. 2-Driftcharacteristic ofthe oscillatorunit, measuredfront a coldstart. Frequency

3.5 Mc.

queney in the 411- or 211 -meter bands andover two-thirds of the 80 -meter c.w. hand.For maximum 01111111t in the high -fre-quency portion of the 80 -meter c.v... band,or the 'phone band, it is necessary to makea slight adjostment of the oscillator out-put circuit.

The amplifier plate circuit when loadedto the normal 60 ma. by an antenna oranother amplifier requires no adjustmentover an extremely wide range of frequency,although a separate control is available onthe panel to 1 li up this circuit when ne-cessary. The plate current of the 807 isa fairly good indication of how the rem! ofthe outfit is working. A 0-100 milliarn-meter is connected permanently in thiscircuit.

Returning to L. the permeability -tuttedmil, we would like to point out that slightchanges in value might disrupt the opera-tion of the entire unit. For example, inone unit built up experimentally it wasdesired to increase the excitation for the807. On the assumption that the gridleak, R3, was absorbing slime of the outputof the 6SK7, an r.f. chlke was played inseries with the leak. The excitation wenttip on 40 and 20 meters, but the circuit nolonger passed sufficient r.f. at 3.5 Me, togive satisfactory operation. Removing

-1000

10 20 30 40 50 60 70TIME -MINUTES

80 90 ha

SHORT WAVE MANUAL 25

the choke permitted normal operation.On 7 Mc. a tendency of the 807 to oscil-

late with the key open in oscillator keyingwas overc by connecting a 20 -slim re-siator in series with the screen,

Mthough not shown in the photograph.additional terminal strips have been madeavailable to provide external grid bias-we believe this is a worthwhile addition, asit prevents oscillation in the amplifier whenthe oscillator is keyed-and to connect anexternal 600 -volt plate supply for the 807iu cases where higher output is required.

While there may be no particular ad-vantage in the key change -over arrange-ment, it was installed in this unit for testpurposes so that the key could be switchedfrom oscillator to amplifier under any par-ticular set of comfit' a to determinewhether or not keying of the oscillator wassatisfactory at all times.

Frequency DriftIn an effort to make this unit compact,

the power supply and all other equipmentwas built on the one ehussis. Naturally,some particular condition,: existed thatmay not exist its some other arrangement -For example, every experimental unitbuilt up proved to have ample stabilityand low frequency drift, although therewas occasionally hunt modulation in thecarrier and in some cases the keying wasnot dean. In all canes, it wan found ne-cessary to by-pass the oscillator heaterright at the tube to clear up hum modula-tion and mantling between the input andoutput circuits. With the addition of thiscondenser, complete isolation was achieved.The output circuit can he tuned throughre:immure, loaded or unloaded, and thereis absolutely no change in the oseillatorfrequency.

The frequency drift encountered in thisparticular mot was mostly caused by theheat radiated by the power transformerand rectifier tube. If the power supplywere not contained in Ilse cabinet, no driftcompensation would be requireol. althoughthe addition of drift compensation can bean asset in any ease. We found that witha 350.41. eflItIpelittatOT the overall drift ofthe complete unit shown in the photographwas quite low. The accompanying curvegives the result of a careful laboratorycheek. It would he imssible to use morecompensation. but it wan not deemed de-sirable because of the danger of overcom-pensation and a reversal of drift some timeduring operation. We are of the opinionthat to have a known drift in a known di.reetion is about the safest bet.

GeneralIt is surprising how mush more effective

low power becomes when the frequencycan be varied at will. We have used thisoutfit just as shown with no additionalamplification for a period of almost foururnntbs at W2AM N. During that timepractically the entire U.S. was worked andthe performance was really remarkable.Of course it doesn't pry to call CQ withthis sort of rig: our practice was to waitfor a (.Q, adjust the frequency of the os-cillator to coincide with that of the otherstation. and then call when the CQ wasfinished. Contacts were numerous andoperation appeared to be just as satisfac-tory as with any NO- or 300 -watt rig weever operated. An this took plat.' in the40 -meter band, which is pretty crowded.

Normally, the amplifier is keyed. Thispermits the "quiet" switch. Si, to he mushfor frequency setting. The oscillator canbe turned on and the signal checked in thereceiver without radiation from the trona-milting antenna. Thus a lot of mineers-sary disturbance is prevented. Everyv.f.o. should have some arrangement bywhich the oscillator can be hulled on andoperated independently .of the nillpitt alit -plilier so it will not cause interference dur-ing adjustments. Finding a place for the'-quiet" switch seemed. at first, to be quitea problem. However. a low -capacityswitch connected between the cathode andthe negative return of the tuned circuitkilled the oscillator and permitted every-thing else to remain the same in the circuitinsofar as current and tube temperaturewere elineerned. One word of warning-the leads to this switch should lie veryshort because if there is appreciable induc-tance iii the switch circuit the oscillatorwill operate even though the switch in

cloned. If the mechanical layout drilla:111Sthat the oscillator tuning unit he mounteda considerable distance from the panel theswitch should be operated by an eatenshaft.

No effort was mode to calibrate the umtill/tow since it was operated in conjunctionwith a calibrated receiver. However, wewould suggest calibrating it and providingsome means of checking it periodically.Our tests have shown that a unit of thistype, if carefully designed and constructed,will remain in calibrate indefinitely, butas a matter of precaution, even though itscalibration can be relied upon the oscillatorfrequency should be checked in the re-ceiver before transmission is attempted.This article is reprinted in pert from June1441 Or

2t, 7'hc HAMMARLUND

Medium Power Modulator

iwerttstedi in Irl,une opera-tion will find this an ideal mummy'

modulator unit. Although it has ntedium110%er output, when used together with anefficient transmitter, its range si hl bealmost unlimited. It will work with eitherthe 812 transmitter or the 815 trans-mitter already described_ Theavailable output of this modulator '1 isin the neighborhood of 65 waits. Natur-ally at ibis level, some distortion will beexperienced, although the quality sill hesatisfactory fora tnateur use. We II Ire I inntlis,serlisa,, and we trust that the readerwill 1101 be horrified to learn that this am-plifier Ilea distortion: all amplifiers havedistortion at certain levels and those thatso 1 excellent over the air, probablyhave more distortion than exists in thisamplifier. Distortionless output e -an beobtained at levels tip to 30 watia.,

F t lamentaliy, the audio power re-quired to modulate an RF amplifier, shouldbe equal to half the DC input of the RFamplifier. Twenty five watts of audiopower will completely modulate 50 wattsinput. tin the other hand, very satisfaetort' radio -phone performative elm he ob-tained with as lit lie as 25 or 30% audiopower. Therefore, it is reasonable to as-tatine that this amplifier can he used withinputs of 150 watts.

The 815 dual hewn power tube, wasselected for this amplifier because of itseconomy and relatively high output atlow voltage. The output transformer,T494 is adjusted for a 4500 ohm outputload. however, this can he changed to meet

almost any load eonditions, providing thetotal power in the load circuit is in Newwith our previous comments on ratio ofaudio to 1)C poser input. The speechamplifier and driver is about the simplestform available and is designed to workwith a crystal or other high impedance lowlevel rnieropl In the speech ampli-fier circuit, we have a 6SJ7 driving a dualtriode connected in a phase invertingcircuit, ibis in turn drives a pair of 6C5 -swhich are used to drive the 815 outputtube.

Extreme ear*, has been taken to main-tain complete isolation in the various highgain circuits. The builder should be pre-pared to adhere closely to the values speci-fied in order to avoid trouble. A departurefrom sonic of these values of condensers orresistors in some of the filters, :night resultin feed -back and instability.

The power supply section of this ampli-fier employs a transformer with a biastap on the high voltage winding: thissupplies negative grid voltage for the out-put tube. Another method for obtaining -this voltage would he to use separate dryLatiprie.s, however. the method used inthis amplifier is more economical in thelong run. Two rectifiers and two Idler sys-tems are required. The 83 mercury vaporrectifier tube is used in the high voltagesupply and 82 is used for the -17 supply.It should be noted that load resistor in theC supply is extresnilly low. A 1000 ohmload resistor is employed to permit goodregulation and re du voltage drop appear-

SHORT WAVE MANUAL 27

These views shim, the general mechanical lay -nos fof the modulator unit.

ing acrLOSS the resigner during periods whengrid rurrent flows.r ThiA entire ottif iRhuill.oil a 17"1,13 x

eltat,.-;is with an 834" x 19" panel. It ranbe ruck mounted or enclosed in a standardcabinet. The panel contains the micro-phone jack. gain control, plate currentmeter and primary switch with its associ-ated pilot light. The output terminals arebrought out at the rear of the eitatgAtk

PARTS LISTPAR METAL

1-Parinetal Chassis, 17 z 13 x 3'1-Black Parmetal Panel, 19 x 8 and 3!4"1-Pair Side Brackets fParrnetai)

KENYON TRANSFORMERS1-T-494 Output trans.t-T-507 Chokel --T-154 Choke1.-T-153 Choke1-T-255 input trans.L-T-216 Power trans.

TUBES1-RCA 60.71-RCA 6N72-RCA 6C51-RCA 815I-RCA 83I-RCA 82

RESISTORSI -111C 3 meg.t-IRC I meg. 1 = watt inetalized

2 watt metalixed

2-IRC 1000 ohm 1/2 watt mecalized3-111C 250,000 ohms 1 . 2 watt metalired2-IRC 50.000 ohms l ,2 wan metalizedt-IRC 3000 ohms L i2 watt metaliaed1-IRC 20,000 ohm 1/2 watt metalized2-IRC 500,000 ohms 112 watt Metuiiied1-Ward Leonard 507-249 1000 ohm

25 watt VAR,1-Ward Leonard 507-749 25.000 ohm

100 watt VAR.1-Ward Leonard 507-139 10.000 ohm

50 watt VAR.1-Mallory-Y 500,000 MP Carbon Con-

trolCONDENSERS

2-Cornell-Dub TLA 6040 4 mfds 600 V1--Cornell-Dub KR -288 8-8 mfds 250 V2-Cornell-Drab EP 9081 8 mfds 450 V2-Cornell-Dub BR 252 25 mfds 25 V1-Cornel1-Dub BR 102 ID cads 25 V3-Cornell-Dub DT 651 mfds 600 V1-Cornell-Dub DT 4P1 .1 mfds 400 V

MISCELLANEOUS

5-Amphenol sockets 8 prong2-Amphena sockets 4 prong1-Pilot assembly for 6 wan -110 V bulbs1-Am cmeoh.enot CL-PCiM closed ckt. input

1-Amphenol MC 1 F Mic. connector1-6 wail 110 V bulb1-S. P. T. Toggle switch f3 amps)3-5 point dummy lugs1-Panel mount fuse holder (3 AG)2-Small feedthru insulators fl irribacht1-"Gain" Dial plate1-Bar Knob-2 amp. fuse t3 AG)

2-Medium grid caps1-A C Line cord with plug

'r 'WSW.% 11/31,1'.11-1[..,.,14.1.15{ unnro,

Magnum of the complete modulator and itN power supply.

28 The HAMMARLUND

Antenna tuningunit which can beused to make upfur a great ninnyart ten n de/icier/ -cies. Wiring enAlgram...4 shier burrit used withUR rimy: t en /74.1.

... ................. .... 11-4.,Y1%.:. I

I I I, I. I 111

RECEIVING and TRANSMITTINGANTENNAS

WHILE radio signals can he receivedon almost any piece of wire, rare

exercised in building a good antenna sys-tem will pay dividends. For general broad-cast and short wave reception, a single wireabout 75 feet long seems to give best resnits. For reception on any particularshort wave band, the doublet is perhapsthe simplest and moat generally used; andit is very effective. This fatter type isrestricted to use over very narrow rangesof frequency. The flat top or main wire ofthe doublet should he wave length long.A convenient formula For calculating thislength is:

468/freq.(mr)For example, a 20 meter antenna (14 me.)should he 33.42 feet long. This is then cutin the center and fitted with a specialtwisted pair transmission line. In attach-ing this type of lead-in. the two terminals atthe antenna should he separated from 12to 16 inches, and the lead-in wires shouldbe spread to form a triangle having all sidesapproximately 16 inches. Make sure thebetter grade material is used for the lead

in. Poor quality here will result in inferiorperformance particularly thiring dampwea titer.

"Trailsmitting Antennas"More complicated antennas are usually

employed fur transmitting, hut here too,the simplesi perform consistently well andit is advisable for the beginner to avoid thecomplicated antennas, sinia he is well upon his theory. The doublet described aboveis best suited where break-in or duplexoperation is desired. There is less interfer-ence due to the feeders not radiating in ornear the operating room. When a similartype antenna is used for receiving and they -are separated several wave lengths, fineresults will be experienced.

Another simple transmitting antenna isone with a single wire feeder. This feederis connected to the antenna at a point re-moved slightly from the center of the eat

Care should Is! taken not to createsharp bends in the lead-in and it should bekept well away from all trees, metal roofs,etc. The distance front the center of theflat top to the point where the feeder is

SHORT WAVE MANUAL 29

I-1 per cent of the total length of the flattop and is the same for each of the impor-tant amateur bands. A single wire feederran lie tapped on the plate coil of the trans-mitter through a blucking condenser or itcan be coupled through a tuning '1.

Time was when nearly every amateurused the Zepp antenna. This is alai, shownin the drawing. In cases where the feedersare an odd number of quarter waves long.the tuning condensers should he 44444

in series. An even number of quarter wavelengths in the feeding system requiresparallel tuning

There are many other types of imped-ance matched antennas. but these requireto knowledge and equipment to getthem operating properly and the beginnerit ill do well to use the simple forms of an:Ictittas. at least until his experience fits himfor the morn complicated EIyaerliA. Thedrawings show a number of methods forconnerting antennas and many methodsI'm. timing them. Most of the diagrams areself-explanatory or are covered in thecaption.

In many locations, eirc stances willdictate the type of antenna to tate. flow-erer, there are a few aimple rules whichrim he followed for all locations: First.

the antenna should be well in the dear andaway from all surrounding objects. Second.it should be as high as poesible and third,all connections should be thoroughly sol-dered. Many amateurs prefer #12 solidenameled copper wire. Usually this typeof wire is difficult to handle and manykinks will remain in the v. ire, particularlyin races where meats arc not strongenough In permit the antenna to he pulledaufficieraly light to remove kinks. Strandedwire consisting of 7 strands of #22 willovercome the trouble with kinks and it ismuch easier to handle. Each strandshould he thoroughly riensiell and solderedwhere a joint is made. The stranded wireworks out particularly well in spacedfeeder systems where it is difficult to main -tam tatanesh.

PARTS LISTHAMMARLUND

2-1502-Standoff insulators

CENTR A1.AlI1-Roury Swi No. 3505.

COIL DATA30 cares No. 14,1ne rd wire2 inch diameter. soured sea length of

3 inches.

Diagrams of various simple antennas with which the beginner may obtain excellentresults. A & N do not require a tuning unit, while the others make Use of theunit shown on the opposite page. In figure the an tenors can be any convenientlength. preferably a 1/4 wave -length or more, but it does not hare to be any enact

length: the tuning unit will bring oboist a match.

30 The HAMMARLUND

LTHOUGH there is nothing compli-AL ea ted about this high voltage powersupply, it is important that good materialsshould he employed and care should beexercised in wiring. The high voltagetransformer has three out -put voltagesranging from 1000 to 1500 volts, which aresufficient to cover the requirements of thehigh voltage artqAiliers described in thisbook. Since this power supply feeds thelast amplifier in the transmitter, filter-ing is not too important. A single chokeof gond quality with a 2 nsf. fit ter condenserwill provide sufficient smoothing to pro-duce a very clear note. The filament sup-ply in the amplifier with which this powersupply will be uscAl, should be containedon the chassis with the real of the powersupply equipment. The switch arrange-nient permits the filaments to be heatedbefore the high voltage is applied. This isquite important because if the high voltage

Wiring diagram for ahigh voltage power sup-ply to be used in trans-

ters requiring at holm sand or more volts.

TRANS-MITTER

POWERSUPPLIES

High voltage powersupply.

were to appear across the tubes before thefilaments were heated, it is more thanlikely they- would be completely ruined.

PARTS LISTKENTON

1-Rect. filament transformer1.-high voltage plate transformer1-Amp. filament transformer1-Filter choke.

1. R. C.

1-50.000 ohm, 71 WI. resistorCORNELL DUMMER

clykanol. 2000 v.R. C. A.

2-866 rect. tubesPARMETAL

1-17" x 13" s 3" chassisMISC.

2-sp. at. toggle switch2-Plate clips for 866 tubes.

SHORT WAVE MANUAL 31

Low VoltageSupply

rrITIS power supply can be used with.1 any of the low power transmitters, de.

seribed in this booklet. or the low powerstages of any high power transmitter. Thechassis used is the standard 7" x 13" x 2."steel unit and provides plenty of space forthe various parts. Since must of the partsof a power soliply become quite but duringoperation, it is important to provide ampleventilation. Do not crowd the parts ormount them in an unventilated containeror cabinet.

While filtering is more important in lowpower stages, this supply with its singlesection filter provides sufficient smoothingto produce a clean, crystal clear note fromany good transmitter. Remember! it isn'talways the fault of the power supply whenthe note sounds bad. Spurious oscillationdue to poor design of the transmitter cando more to spoil a signal than even thepoorest filter. The single choke with inputand output condensers will produce excel-lent results if not abused by overloading.

The transformer contains all windingsfor filainelit and high voltage. With con.

Drilling dimensions forthe low rulings. powersupply. Sufficient fil-tering is obtained withone choke and t tro con -

densers.

74 clew of lute miragepower supply. This willwork with all transmit-ters requiring around

400 rolls.

denser input to the filter, a full load voltageis just ubrutt equal to the 400 voltage ratingof the secondary of the transformer. Withcondenser input it is advisable not to usea mercury vapor rectifier. The 51.3 givesthe best results. One very important partof this power supply is the fuse, by allmeans include a fuse in every power supplyyou build, it costs very little and will paybig dividends. Even if it only saves a t ohsin case of overload due to a short circuit,you will be way ahead in dollars and cents.

PARTS LISTIIAMMAR LUND

1-5.4, Citrons socketI. R. C.

1-20,000 ohm, 50 wart resistorAEOROVOX

2-8 mf. 500 V. electrolytic colds.STANCOR

1-Plate.61. transformer No. P.4081 (seetext for using}

1-Filter choke 20 H. 175 ms. No. C.1 410R. C. A.

1-57.3 tubeMISC.

1-Tosele switchPAR METAL

1-7' x 13' 2' chassis

Oaf) ,c,,.)7------.-1-

.

).,i

41-4- Ak :64 G 14 C3-41 N "L"il &in /; A.....-. q_erva ftA -r

-

t " e1'

13)

qQOUCTs

4cca

42-

AbR

Dixie PZ. E' !1Y Co.,11

Charlotte, North Carolina