all 7 screen grid secrets! - americanradiohistory.com · rear view of the hbh kirplane cloth...

All 7 SCREEN GRID SECRETS!15

CENTS

REG. U.S. PAT. OFF.

The First and Only National Radio Weekly

TUNING EQUAL

KARAS FRANCHISESHORT WAVE LAW WINS

RECEIVER IN CONGRESS

SHOOTING CUSTOMTROUBLE IN SET BUILDERS

SCOTT'S ANSWERSUPER QUESTIONS

FINE EYE APPEAL IN ALUMINUM SUBPANEL

TA- TV:fgnMTZSSEiea.i-TNINEMM.

A New Opportunity for Attractive Construction is Afforded by a Self -Bracketing Aluminum Drilled Subpanel, withAffixed Sockets. See Page 3.

HOW A NOVEL A SUPER DOUBLEELECTRIC AND EFFECTIVE THAT FITS MODULATION

BRAIN MIXER IN YOUR TESTS FORWORKS CIRCUIT AUTO HOME

RADIO WORLD April 7, 1928

Gen u ne HBH StiffeningFluid, ecret compound, withsuperlat ve effect on tonequality. L a r g e sized can,enough for three Coats. Cat.No. 1097 $1.50

"DOPE"111311 Stiffening Fluid may beused on any cloth typo speakerto great advantage. It is ofspecial manufacture, secretformula, and noted for supe-rior effects on tone quality.'two coats will suffice. Threeere slightly better. Larges 1-z e can, enough for threecoats. When the first coatdries, in 15 minutes, a spe-cial speed feature, apply thesecond coat. When that driesput on the third and lastcoat. Cat. No. 1097..51.50

Rear View of the HBH kirplaneCloth Speaker

Size, 18x24 Inches

All Ready to Play withAmazing Fidelity

H.B.H.AIRPLANE CLOTH

SPEAKER"The Speaker ThatSpeaks for Itself"

Size 18x24 inches, factory -constructed.All ready to play. Cat. No. 1088.

Front View of the HBH AirplaneCloth Speaker

Size 18x24 Inches

$11.00OTHER SIZES OF FACTORY -MADE MODELS

18x36" Cat. No. 1089....$13 24x36" Cat. No. 1090....$14 36x36" Cat. No. 1091....$16Any factory -made HBH Speaker, or complete kit, less unit, deduct $3.75.

COMPLETE KITS AND SEPARATE PARTS FOR HBH AIRPLANECLOTH SPEAKER

The HBH Airplane Cloth Speaker may be purchased com-pletely made up, in factory -sealed cartons, at the prices listedabove, but if you prefer to build the speaker yourself youmay do so at a saving of from $1 to $2, depending on the sizeof the speaker.

The complete kit consists in each case of airplane cloth,frame, moulding, unit, stiffening fluid, apex, crossarm, brack-ets, long cord, apex, hardware and instruction sheet.

We sell separately everynouncements below.

CLOTHGenuine airplane cloth sameas used for best airplanes;great tensile strength, lightweight, Govt. specifications.18x24." (with 757 for baffle).

Cat. No. 1099 $1.5018536" (enough extra to cut

o w n baffle with shears).Cat. No 1100 $1.80

34536" (enough extra to cutown baffle with aheand.Cat. No. 1101 62.00

36536" (enough extra to cutown baffle with shears).Cat. No. 1102 $2.50

Complete Kit, 18x24", Cat. No. 1109 $10.

Everybody wants a first-class speaker,because no set or power pack is anybetter than the speaker it feeds. Nowthe general public is enabled to obtainthe famous HBH Airplane ClothSpeaker, both in factory -assembledform and in kit form, as well as eachindividual component of the kit sepa-rately, and thus can obtain a wonder-fully clear -toned and faithful repro-ducer at the lowest cost at which suchfine results are generally obtainable.

component

FRAMEThe wooden frame. with cop-ing of decorative moulding.may he purchased in standardsizes and used as such, ormay be cut down from alarger standard size to asmaller special size, and clothcut by purchaser accordingly.The frames come completewith moulding and hardware,in factory sealed Barton.18524" Cat. Na 1103.55.0018538" Cat. No. 1104. 5.2524538" Cat. No. 1105. 5.3536a36" Cat. No. 1106. 5.50

of the kit. See an -

APEXThe apex le of the doubletype, so that one metal shieldis placed outside the dia-phragm and the other inside.but the same apex may beused on any type of con,speaker. Each ex isequipped with threaded sleeveand thumbnut for fasteningunit drive. Highest qualityand durability of metal used.Outside diameter of apex,114". Guaranteed to be en-during and serviceable.Cat. No. 1107 , 25e

Complete Kit, 24x36", Cat. No. 1110 $12

Those who have special cabinets, consoles,phonographs, etc., into which they want tobuild a fine speaker, have every opportunitynow to build a speaker that will create asensation. It is very simple to make thefamous HBH Airplane Cloth Speaker any sizeyou want. Determine the size desired, andmultiply the dimensions in inches, thus ob-taining the number of square inches. Multiplythis by three cents to obtain price. Thensend cash, check or money order with yourorder, as odd size kits are not C.O.D. items.All else are. Or you may order the nextlarger standard size C.O.D. and cut it downyourself. In either case you get complete kit.- - -

GUARANTY RADIO GOODS CO.,145 West 45th Street, New York City

Ship, me the following items as advertised in Radio World:

Cat. No Cat. No Cat. No

Cat. No Cat. No Cat. Nofor which I will Par Postman advertised price plus few cents extra for postage

Name

Address

City StateFive -Day Money -Back Gauranty

OgnitatigPowerful unit, excellent forany cone or similar typespeaker, standard for HBHspeaker; very loud. Cat. No.1098 $3.75

UNITThe unit is the Powertonemodel. which provides highdegree of volume and yet issensitive. Stands great strain_Died successfully in all radioreceivers, including Dowerpack installations up to 550volts on the plate. Up to135 volts DC may be passedthrough coils of unit with-out damage. For higher volt-ages altered output is recom-mended, but unit has longstood up to 180 v. unfllteratCat. Ste. 1108 53.75

Complete Kit, 36x36,', Cat. No. 1111 514

The story of the excellence of theHBH Airplane Cloth Speaker is besttold by the speaker itself. As allgoods are sold on a five-day money -back guaranty, you run no risk. Alsoyou SEND NO MONEY. Have oneof these speakers in your home andlet your friends, too, compliment youon the fine tone quality and volume.And, besides, think of all the real en-joyment you get yourself from thebest speaker in the low -price range.

REPLACEMENT COILSYou may have a unit in which there is nothing wrongexcept that the small coil built into it, or one of the twocoils, or both, are burnt out. Replace these coils and youhave the same old fine unit. These coils are hard to get,but we have plenty of them in three different sizes. Whenordering, state the dimensions of the bobbin, or, preferably,send your old coil and we will send the correct replace-ment coil. Cat. No. 1112, each, 75c.UNIT MOUNTING BRACKET. Cat. 1113 35c

GUARANTY RADIO GOODS CO.145 West 45th Street New York City

"UNINTERRUPTED READER INTER ESEVERY WEEK EVERY YEAR

Vol. XIII. No, 3 Whole No. 315APRIL 7, l9ffi

15c per Copy. $6.00 per Year[Entered as second-class matter, March,1922 at the post office at Ness York, N. Y.,

under Act of March 1S79]

RADIO WORLD

Technical Accuracy Second to None A N\RA O, kit it . 1,01 1.1.

I I i+ Veit .15th

Design Analysis of theShield Grid Diamond

THE use of the new screen grid tube1 as the radio frequency amplifier inthe popular four tube circuits, using aregenerative detector, as for instance theScreen Grid Diamond of the Air, carrieswith it definite advantages. Provided thatan ample -sized primary is used in thethree circuit coil, the amplification is in-creased tremendously, when one considersthat the gain in the first tube is squaredby the detector and the total multiplied ataudio frequencies.

The amplification in that first or RFtube may be made even higher if theplate voltage is increased or the numberof primary turns is made larger, or if bothmagnification opportunities are seized.

This all-important primary, the smallerfixed winding on the three circuit tuner,if too large, will cause the RF tubeto oscillate, and will reduce selectivity atnormal operation. Therefore the chosencoil, a Hammarlund HR 23 three circuittuner, represents a good compromise,since it has a rather generous primarywhen the entire winding is used.

Twice Ordinary Primary

The coil was originally designed for theHammarlund-Roberts circuit, hence theHR, and has a midtap on the primary, forconnection of a neutralizing condenserTherefore the total winding was twiceas large as on the other types then pre-valent. By disregarding the neutraliza-tion tap, since the screen grid tube re-quires no neutralization, and by connect-ing plate of the screen grid tube to oneterminal of the primary, and B plus to"the other, a suitable degree of amplifi-cation is achieved and the usual lossesincidental to neutralization are avoided.

Those who desire a still larger primary,either on such a coil or some other, mayobtain a tubing that will fit inside ofthe secondary of the coil, without inter-fering with motion of the tickler, andput on 35 turns of any kind of insulatedwire from No. 30. to No. 24. This newprimary may be secured to the subpanelby two diametrically opposite right-anglebrackets, which of course are affixed tothe new coil for support. At any eventa skinny priniary on the three circuitcoil must not be used.

The plate voltage on the screen gridtube may be high, and should be 135 atleast. Up to 150 volts are permissibleunder the automatic: system of negative

14 H. B. 11,1),/,1/1

r1

35TURNS

OPWIRE

SIDE VIEW OF A SPECIAL PRIM-ARY WHEN INSERTED IN A THREECIRCUIT COIL (DOTTED LINES)FOR THE USE OF A SCREENGRID TUBE. THE EXISTING PRIM-ARY ON THE THREE CIRCUIT COILWOULD BE IGNORED IN SUCH AN

INSTANCE.

grid bias used in the Screen Grid Dia-mond, whereby the voltage drop in theNo. 622 Amperite is capitalized.

Improves Selectivity

As the voltage source is 6 volts, and thefilament voltage is 3.3, the negative gridbias, obtained by connecting the gridreturn to minus A, is the difference, or2.7 volts. The grid is thus made 2.7 voltsnegative in respect to the negative fila-ment.

This is a little more than the bias rec-ommended on the slips enclosed in thetube cartons, but is highly satisfactory,nevertheless, because the extra negativebias proportionately increases the inputimpedance, and improves selectivity. Sinceit is very easy to use a screen grid tubein circuits that provide tremendous am-plification at the expense of selectivity,the extra bias is a step in the right direc-tion. Also, it enables the application ofthe 150 volts.

The standard hookup is shown herewithfor the first time in pictorial diagrammaticform. Those who desire to build thecircuit, recognizing that it possesses out-standing virtues in distance -getting, selec-

tivity and tone values with a maximumvolume that reaches almost incrediblelevels, and all at small outlay, of coursewill follow the life-sized point-to-pointpicture diagram published in the officialblueprint, where the schematic diagramalso is given.

An Innocent QuestionOne man, who introduced himself as one

who didn't know the first thing aboutradio, proceeded to prove it by saying:

"\Vith all these six, seven, eight, nineand ten tube circuits on the market, howcome that it is possible to get satisfactoryresults with a four tube set? Aren't eighttubes twice as effective as four? Don'tthey get stations twice as far off, or thesame stations with twice as much vol-ume?"

Well, that depends on a variety of fac-tors, as was explained to the innocentinquirer. One nine eight -tube circuit, forinstance, has an amplification factor twen-ty times as great as that of the ScreenGrid Diamond, whereas faulty design andincorrect choice of parts easily could makean eleven tube circuit inferior to a fourone.

Efficiency Sacrificed for ConvenienceAs for the run of five, six and even

tube factory -made receivers, it is a rec-ognized fact that the public that buyssuch sets is a convenience -loving aggre-gation, hence single dial control, evenwithout trimming facilities to compensatefor inequalities in tuning that science cannot well avoid, are produced.

This usually means that one or twotubes are used simply to make up for theloss due to dissonance produced by singledial operation. The chain of RF tubescauses self -oscillation even at a low broad-cast frequency (high wavelength), so"lossers" are introduced, and before we'vefinished we find that three stages of TRFahead of a plain detector tube may notperform as well as one decent RF stage.i.e., a four tube set may surpass in per-formance a six tube set.

On the question of cost, the four tubereceiver requires fewer sockets, coils, tun-ing condensers, neutralizers, tubes, less Aand B current and no ganging. For agiven amount of space the parts may hespread out more effectively, with a dis-tinct amplification and stability gain, dueon the one hand to absence of eddy cur-rent losses and on the other to absence


",firgra7L-71# -17,,v-

PLAN OF THE FRONT PANEL OF THE FOUR TUBE SCREENGRID DIAMOND OF THE AIR. THE ELLIPTICALHOLES SHOWN IN DOTTED LINES BELOW THE DIAL CENTER -CAPS ARE FOR THE ANCHORAGE OF THE MAR-

CO DIALS.

of squealing that requires still further"lossers" to keep the set quiet in opera-tion, or make it operable at all.

Regeneration's EffectAs if this were not enough, a four tube

set of proper design, as compared witha multi -tube factory -made set that servesconvenience first, may have the detectortube regenerative, which enables an in-crease in the amplification at radio fre-quencies even to a thousand -fold, or more,so that weak signals are strengthened,greater distance traversed, and at thesalne time selectivity sharpened, say, 200per cent.

Thousands of persons have built theDiamond of the Air in the three and ahalf years this circuit has been featuredin RADIO WORLD. Incidentally, noother publication has featured one cir-cuit so long, and so successfully. Now19,000 blueprints have been sold. Thecircuit has been essentially the same allthe time. This year the Screen GridModel was brought out, which changesonly two connections.

The value of substituting the screengrid tube. for the 01A tube has been con-clusively demonstrated. Delighted usersof the Screen Grid Model attest to the

. supremacy of the circuit.Sonorous Audio

The radio frequency level is well bal-anced and effective, in the present reign-ing success, and is followed by a highlyefficient and sonorous audio channel, con-sisting of two Karas Harmonik audiotransformers, which have a tone unex-celled by any other transformer in thesame price class.

Hence, to sum up the circuit, we havea TRF stage that attains a degree ofamplification not dreamed of last year anda regenerative detector, with each of thesetwo circuits separately and individuallytuned. (If two condensers were used onthe same shaft or otherwise actuated bythe same main dial, a trimming condenseror inductance would have to be used, andthis, too, would constitute each of thetwo circuits separately tuned.) The audiochannel is two stages of transformercoupling, because the highest degree ofvolume per tube is thus obtainable, con-sistent with stability, while quality remainsexcellent. Other forms of audio mightprovide better quality, but always withlower efficient efficiency per tube-threetubes might be needed where two areused now.

Fine Appearance Made EasyThere is one comparative point not yet

even hinted at-the appearance of thehome -constructed receiver. It is admit-ted that many who build sets for their

own use and enjoyment are not the mostskillful compositors of radio parts intoa finished receiver.

Placement of parts may be done poorly,and that is the main short -coming, butthis is overcome by following a blueprintthat is an exact duplicate of the wiring,at every point and angle, as laid outby the designer of the circuit himself.The official blueprint of the Screen GridModel Diamond is an exact copy of myown receiver.

Then there is the important subject ofthe subpanel. If a baseboard is used,anything approaching fine appearance isnext to impossible. The day of the base-board is gone forever from the sphereof the custom built or home -built set, just

LIST OF PARTSVital Kit

One Hammarlund HR 23, coil kit, con-sisting of one antenna, coupler and onethree -circuit coil, both for .0005 mfd. tun-ing.

Two Karas .0005 mfd. SFL condensers,type 23.

Two Karas Harmonik audio frequencytransformers.

One No. 622 Amperite with mounting.Three No. 1A Amperites with three

mountings.One Lynch 5 meg. grid leak.One Volume Control Clarostat.Three Aerovvox .006 mfd. fixed mica

condensers.One Aerovox .00025 mfd. mica grid con-

denser, with clips.One .001 mfd. Aerovox mica fixed con-

denser.One Yaxley No. 10 battery switch.One Yaxley No. 310 pilot light bracket

(lamp extra).Two Ely binding posts (Speaker -I-,

Speaker -).Two Eby binding posts (Ant., Gncl:).One 7 x 21 inch Bakelite front panel

(already drilled.One 10 x 20 inch aluminum self -bracket-

ing subpanel with four built-in sockets(subpanel already drilled for all holes).

Two Mar -co dials.One Pee -wee clip (No. 45 Universal

clip).ACCESSORIES

One Vac -shield for shielded grid tube.One shielded grid tube, CeCo RF 22.One CeCo type H, special detector tube.One CeCo type A.One CeCo type F (112)One roll flexible Acme Celatsite.One 7 -lead battery cable.One set of cable markers.Two dozen lugs.One HBH Airplane Cloth Speaker.A, B and C supplies.

as surely as it is gone from the field offactory -made receivers.

Aluminum Subpanel

A man wants to build for himself or forothers professionally, a receiver that, tubefor tube, ontperforms the others, yet atleast equals them in eye appeal.

Hence why not turn to the same sourcethat supplies the set manufacturer, anduse a genuine aluminum subpanel, of theself -bracketing type, with built-in sockets,to which one may affix a Bakelite frontpanel, already drilled for the Yaxley pilotlight and switch, two Karas variable con-densers, Hammarlund tickler coil andVolume Control Clarostat-holes of stand-ard size, by the way, so that no incon-venient situations arise.

This opportunity is here, for a self -bracketing aluminum subpanel and adrilled front panel for the Four TubeScreen Grid Model Diamond of the Airare now commercially produced. All holesare drilled for all specified parts and allleads, and insulators are seconded wherenecessary. If you are interested in suchconstruction of the receiver, further in-formation will be gladly furnished if youwill address me: H. B. Herman, c/oRADIO WORLD, 145 West 45th street,New York City, as I am now collatingfull information.

Lynch Resistors Used

Another form of, the Four Tube Dia-mond comprises two screen grid tubes,the second one being the detector, andin that instance the first audio stageshould be resistance coupled, using .1 or.05 meg. Lynch metallized resistor for theplate circuit, 2 meg. for the grid cir-cuit, and a .01 Aerovox stopping conden-ser. The grid leak remains a Lynch 5meg. metallized product. The holes onthe aluminum subpanel are so drilled as totake care of these parts if the spacecharge (screen grid) detector circuit ispreferred. The seconh audio stage re-mains transformer coupled.

A different blueprint is published forthe Diamond using two screen grid tubes,and is known as the Space Charge De-tector Diamond of the Air blueprint.

In either event, if the constructor pre-fers to drill his own subpanel, he maydo so from the information contained ineither blueprint, or if he desires to drillhis own front panel, he may follow thedata contained in the front panel diagrampublished herewith.

In both types of circuits the front panelis the same.

A 222 Vac -Shield should be placed overthe screen grid tube, whereas it is a goodplan to use a 201 A Vac -Shield over thedetector tube, too.

,

cpill

yx ..s

.,

1

e+

O`I

i'...

.In

II

1

..,..

,4.

I-`

"'.i

.I;

t.,...

..I

'

/')'

% )

':7

,

I/ /

I

AN

I-,

II'

./

.,,.5

inE

IG...

I X

, FD

,VP

-/, /

1.er

.1

s' N

.//

/I

/,-

-- -

._''s

,e-

11t

ti

t' t

,i

t

ivy'

...__

/ ---

-1 v

:-/ :

-1(f

iz,

.....

cp...

.."'"-

......

..A

A...

DR

OP

I...

Z5

0....

__.

1/-

v.j1

,...

.,,

......

......

.....

//--

--...

......

...,^

/-\

....0

4,..'

"

..---

roC

AP

' ON

TO

P//

OF

-22

TU

BE

/-.

'VA

,\

/'

BO

TT

OM

.

/'

......

1--

......

.<44

,,e

'...-

:-;-

...,..

...t

-....

itzc

7-/

/LO

G

.P.

N. F

+

//(7

/IF

IXE

D C

ON

GA

I'

r .0

06 /7

7 F

D;'

.

\''f)

TH

RE

AD

TH

RU

/N

.H

OLE

AN

D/

:"...

./:7

-:..Q

.?..

N,S

OLD

ER

T0,

1_'..

..F

R.R

IIE /

I

'/

WIW

IM

IMI

rIM

IZIM

ISZ

EN

E1

r1\

1I

FIX

ED

CO

NT

4.I

rr

r 1

.006

mro

.::ot

% l

-- -

-

,..N

. .9

75.

US

E T

WO

HE

XA

GO

NA

L N

UT

ST

O E

XT

EN

D c

oIL

. i"

BA

CK

TO

CLE

AR

FR

AM

E O

F"

VO

LUM

EC

ON

TR

OL


Tune in the Short Waves

FIGS. 5 AND 6ON TOP IS A VIEW OF THE AERO COILS THAT AFFORD A RANGE OF 13TO 725 METERS WHEN USED WITH A KARAS SHORT WAVE CONDENSER.THE PRIMARY OF THE INDUCTANCE SYSTEM IS ADJUSTABLE (LOWERVIEW), WHICH ASSURES HIGHEST EFFICIENCY FOR THE RANGE ONEIS WORKING ON. WITHIN THAT RANGE-ANY GIVEN SECONDARYDEPICTED ABOVE-FURTHER ADJUSTMENT IS NOT ABSOLUTELY

NECESSARY.

THE fact that a single tuning conden-ser is used in the Karas short wave

receiver described in the March 31 issueof RADIO WORLD makes the circuitextremely easy to tune. There is no in-tricate dial setting combination to solve.Just one sweep of the single dial fromzero to maximum covers the entire rangeof the coil in use. No station within oper-

ating range of the receiver escapes, pro-vided that the condenser is not turned toorapidly.

Turning of the condenser too rapidlyis not likely with the Micrometric, forthat dial is truly a slow motion tuning aid.By that is not meant that it has one ofthose ridiculously high gear ratios whichrequire an hour for turning the conden-

J. E. ./Inde?voi,ser from one extreme to the other, butthat it has a practical ratio. It turns thecondenser slowly enough to insure thatall stations be heard, yet not so slowly asto incite the impatience of the operator.

The ease of tuning is d neatly increasedby the special cut of the condenser plates.They are cut to straight line frequencycapacity variation. This is a feature ofutmost importance in a short wave receiv-er in which the stations may be crowdedclosely together. The condenser spreadsthese stations out in direct proportion tothe frequency. The advantage of thiscannot be fully appreciated except whentuning in the short waves:

In constructing the receiver it is im-portant that the rotor plates of the con-denser be put on the grounded side of thecircuit and that the stator be connectedto the grid side. This eliminates bodycapacity and greatly facilitates the separa-tion of short wave stations as well askeeping the "tune." Also it is vital touse a dial with no metal part exposed, andthe micrometric is just that.

Just as it is important to ground therotor plates of the tuning condenser, soit is important to ground the rotor platesof the tickler condenser C2. The statorof this condenser should be connected tothe tickler coil L3. The advantage of thisconnection is great when a weak stationis being coaxed in and when the circuitis brought up to critical regeneration.Be not misled by the circuit diagram inthis respect, but follow the wiring dia-gram Fig. 4 in the first part of this ar-ticle.

Inductance ChangesThe apparent inductance of the tuning

coil L2 changes as the regeneration is ad-vanced. As the capacity of the ticklercondenser is turned up the apparent in-ductance of coil L2 increases, and it isnecessary to decrease the capacity of Clto keep the circuit in exact resonance withthe signal frequency.

A good practice in tuning is to set thetuning condenser a little below the pointwhere the signal is maximumbefore ad-vancing the regeneration. Then as thetickling is increased the apparent increasein I2 offsets the lack of capacity in Cl.The optimum combination of tuning andtickling is thus arrived at much morequickly than when the circuit is returnedevery time the tickling has been changed.

Of course the two condensers can be man -

High Frequency Phenomena Give aA few years ago short waves were called

freakish 'because sometimes signals werereceived from tiny transmitters thou-sands of miles away with simple receivers.The waves seemed to violate all the lawsgoverning radio waves, or thought to gov-ern radio waves. They did not at all be-have like the longer and more familiarwaves.

Long waves, such as were used inbroadcasting and commercial radio tel-egraphy, did not travel so well in the day-time as at night. Some of the shorterwaves on the other hand seemed to travelmuch better in daylight than in the dark.Where long waves attenuated at a fairlydefinite rate with distance, short wavesseemed to increase or decrease in strengthin a perfectly haphazard manner. Theorypredicted that short waves should atten-uate much more rapidly with distance than

long waves, but actual results partiallydisproved the theory.

They Skip AroundAnd then it was discovered that the

short waves advanced over the surfaceof the earth in kangaroo fashion. Theymade one gigantic leap and came down toearth hundreds of miles away, or eventhousands of miles. In the space betweenthe transmitter and the receiver locatedwhere the waves came down after a longleap they could not be received with evenhighly sensitive equipment. Where theycame down a very simple receiver sufficed.

When this apparently erratic behaviorof the short waves was studied the skipdistance theory was advanced to explainthe action. The more data collected onthe behavior of the short waves the betterdoes the skip distance theory explain the

action, the more order is seen in the ap-parently haphazard travel of the waves.

The Heaviside LayerThe skip distance theory assumes that

the so-called Heaviside ionized layer inthe upper atmosphere is a fact. Thislayer acts as a mirror which sends thewaves down to earth after striking it, oras a refractor which bends the waves soas to follow the curvature of the earth.Abundant data have shown that thistheory is in agreement with observedfacts.

The distance up to the Heaviside layerhas acutally been measured. And it hasbeen found that the layer rises and fallsaccording to the amount of sunlight. Itmay descend to a region 200 miles abovethe surface of the earth, or even lower,and it may ascend to 400 miles or above.

it

li

April 7 1928 RADIO \\ ORLD 7

ithout Missing a StationWTechnical Editor

LIST OF PARTSCl-One Karas .00014 mfd. variable con-

denser.C2-One Karas .00025 mfd. variable con-

denser.C3-One Sangamo .0002 mfd. fixed con-

denser with clips.C4-One Sangamo .001 mfd. condenser

(across sec. of T2).TI, T2-Two Karas Harmonik audio

frequency transformers.RI-One 4 megohm Durham grid leak.R2-One No. 112 Amperite unit.Rhl-One Yaxley 20 ohm rheostat.S-One Yaxley No. 10 filament switch.

L3-One set of Aero short wavecoils (see text).

L4-One Aero radio frequency No. 60choke coil.

Two Yaxley phone tip jacks.Two Karas Micrometric dials.Two Karas sub -panel brackets.Three Benjamin sockets.Eight X -L binding posts.One Bakelite 7x18x3/16 inch panel.One Bakelite 8x17x3/16 inch sub -panel.

ipulated simultaneously, in opposite direc-tions, to arrive at the optimum combina-tion still more rapidly. With a little ex-perience it is possible to keep the twocondensers in exactly the proper relationall the time.

Choice of Battery TerminationSome builders prefer to bring all bat-

tery terminations to a strip of bindingposts while others prefer to bring themto a cable connector terminal. This re-ceiver has been assembled to satisfy bothof these classes of fans. Of course itmakes no difference in the operation ofthe circuit. It is simply a matter of con-venience. Fig. 4, which is a tracing ofthe official blue print, shows the arrange-ment of the binding posts when thatmethod is selected.

If a cable terminal connector is selectedall the battery terminals are brought tothis connector. In this connector all theterminals are marked and colored accord-ing to RMA standards.

The set of coils used to cover the rangefrom 13 to 725 meters is shown in Fig. 5.The largest coil at the left covers therange 235 to 550 meters. By connectinga 100 mmfd. condenser in parallel with this

THETHE

_1..11111111111111111111,

,10,;1

FIG. 7SECONDARY COIL DETERMINES THE WAVELENGTH RANGE, SINCESAME TUNING CAPACITIES ARE USED FOR ALL COILS. IT IS ONLY

A MOMENT'S WORK TO PUT IN ANOTHER COIL.coil the range is extended to 725 meters.The smallest coil at the right covers therange from 13 to 29.4 meters. The sec-ondary of this coil contains only threeturns of wire. In Fig. 6 this coil is shownmounted in its receptacle. It is coupledclosely to the antenna coil, which can beseen at the left. To loosen the couplingthe antenna coil should be inclined at anangle to the three turn coil.

Changing CoilsFig. 7 shows the rear view of the com-

pleted set and indicates how the-coilsare inserted into the receptacle. Note thatthis receiver has ben built with a cableterminal connector instead of bindingposts. Receiver Layout

The arrangement of the parts on thepanel is indicated on the panel view Fig.2 and on the wiring diagram Fig. 4. Allthe necessary dimensions for layout of thepanel are given on the upper half ofFig. 4, and all the necessary dimensionslaying out the sub -panel are given on thelower half. Every lead and connection

is also distinctly shown in Fig. 4 so thatthere is no chance -of going astray in wir-ing the circuit. '

Whereas only 5 coils are shown in Fig.5 there are actually six in the completeset. If No. INT-0 Is used the range isfrom 13 to 29.4 meters and if No. INT-1is used the range is from 15 to 33.5 me-ters. The next coil No. INT-2 covers therange from 31.5 to 68 meters. The small-est coil is used mainly to increase therange from 15 to 13 meters. The com-plete set of aero coils follows:No. INT-0 13 to 29.4 metersNo. INT-1 15 to 33.5 metersNo. INT-2 *No. INT-3

31.5 to 68 meters57 to 133 meters

No. INT-4 125 to 250 metersNo. INT-5 2.35 to 550 meters

[The first presentation of the Karas ShortWave circuit was published last week. Anyreader who desires a blueprint of the circuitmay obtain a cotnplimentary copy by addres-sing J. E. Anderson, Technical Editor, RADIOWORLD, 145 W. 45th Street, Al. Y. City.]

*sac Appeal to ReceptionThe propagation of all radio waves is

affected by the layer in a manner depend-ing on the altitude of that layer. Butshort waves are particularly affected. Forexample a short wave may strike thelayer when it is 200 miles up, rebound -andcome down to earth 400 miles. from thestarting point. It may again leave theearth only to be thrown back by the lay-er and come down another 400 miles away.

The Rise and FallWhen the layer rises to a higher alti-

tude the skipped distances on the earthmay be much greater. In fact there maybe only one rebound. Since the regionof reception of the short waves is thatwhere they come down it is apparent thatthe distance of reception depends on thealtitude of the Heaviside layer, and sincethat in turn depends on the sunlight it

is apparent why reception varies with thetime of the day.

Waves of all lengths do not behave inthe same manner. Hence a 20 meter wavemay be the best for communicating be-tween two given distant points at onetime of the day and a 40 meter wave atanother.

The vagaries of the short waves havebeen carefully studied and it is now wellknown what wave length is best betweeritwo given points at any time of the day.Commercial companies may have onewave for the night operation and anotherfor day time operation. The transmittersare arranged so that the operators canchange quickly from 'one wave to theother and thus avoid any interruption inthe service.

Fading is closely associated with theHeaviside layer and the reflection of

waves. If the altitude of the layerchanges the strength of the received sig-nal in any reception region will changealso. If the layer rises and falls the sig-nals will wax and wane. This explainsslow fading.

The explanation of rapid fading may befound in the fact that at any given pointsignals will reach a receiver both by thesky route and the earth route. The twocomponents of the waves may arrive atthe receiver so as to strengthen the totalsignal effect or so as to weaken it. Ifthere is any change in the effective dis-tances of travel, either by the sky route orthe earth route, the degree by which thetwo components will strengthen or weak-en each other varies, and this variationis fading. The variation may be slow orrapid. Fast fading may cause a squeal inthe speaker.

8 RADIO WORLD April 7, 1928

Screen Grid Coil DesignONTRARY to the prevalent impres-

t....4 sion among radio experimenters, itis not essential to employ a tuned plateimpedance in connection with the newscreen grid tube when this tube is used asa radio frequency amplifier. That issimply on method of coupling the tube totake advantage of the properties of thetube. But the tuned impedance methodis subject to certain disadvantages whichmay be avoided by selecting another typeof coupling. One of these disadvantagesis the lack of selectivity and another thetendency toward instability of the current.

A necessary condition for getting ahigh amplification out of the screen gridtube is that the useful load impedance inthe plate circuit be high. This conditioncan be satisfied with a radio frequencytransformer having a large number ofturns on the primary and then tuning thesecondary in the usual manner.

The method of coupling retains theselectivity of the circuit and is morestable than the impedance method.Shielding and neutralization may be dis-penced with entirely.

When the screen grid tube is coupledwith one radio frequency transformer ofthis design and 'followed by a regenerativedetector the circuit is so sensitive that it

By Hemstreet Hillesbecomes impractical to use an ordinaryantenna. The signals brought in would beentirely too intense. So a very smallantenna may be used, even one of four orfive feet of wire. For example, a pianohinge would be entirely adequate.

The use of such a small antenna greatlyincreases the selectivity of the circuit andmakes it possible to tune in distant sta-tions while the locals are operating. Forexample, with a National Shield Grid Fivereceiver constructed in this manner andoperating in Boston, WJZ was broughtin from Bound Brook, N. J. while WNYCin Boston was going. The frequencyseparation of these two stations is only10 kc.

The satisfactory operation of this re-ceiver in a large measure is due to thehigh impedance slot -wound primary onthe coupler between the screen grid tubeand the detector. The high impedance ofthe winding extracts from the screengrid tube a large proportion of the totalsignal voltage in the plate circuit of thetube. If a tuning coil is closely coupledto this high impedance primary the highvoltage is transferred to the secondary,and thence to the grid of the detectortube.

The special, construction of the National

Layout of Parts forBreadboard Unipac

A simple way of building the Silver -Marshall AC audio amplifier and powersupply (either 881-250 or 882-250) is toput all the parts on a wooden baseboard.This also affords a free ventilation of theparts. Everything is out in the openwhere the heat generated can escape asfast as it is liberated. This is an impor-tant feature in power amplification whereconsiderable heat is liberated by tubes,transformers, resistor strips and evensome by condensers.

If heat is not removed from these partsthe temperature rises to a dangerouspoint. The wax in the condensers softensand melts, insulation on wires becomesdamaged and the circuit as, a whole losesefficiency.

A suitable layout of the breadboard typeis shown in the accompanying diagram.At the left are the S -M328 power trans-former and the S -M filament transformer.In the middle are the various by-passcondensers and the resistors, and at theright are the audio frequency transform-ers, the S -M 331 Unichoke and all thetubes.

The two large tubes at the extremeright are the two -81 half wave rectifiers.The remaining large tube is the -50 typepower tube. One of the small tubes isa -26 type, tube used as an audio frequencyamplifier ahead of the -50 power tube.

The other small tube is a -27 heater typetube which is used as an audio frequencyamplifier between the phonograph pick-up unit and the audio frequency ampli-fier.

A large baseboard should be used sothat there is plenty of room for all theparts. Crowding is not consistent withthorough ventilation and cool operation.There is also room for the voltage regu-lation tube, in case one is used, as is ad-vised.

An important feature of this unit is themanner in which the phonograph pick-upis coupled to the audio amplifier. Theordinary method is to connect the pick-upunit in series with the primary of thefirst transformer. The result of this coup-ling is mediocre at best. But in this cir-cuit the pick-up unit is coupled throughthe medium of a -27 type tube. That isthe pick-up is connected to the grid -cir-cuit of the tube and then the first audiotransformer is connected to the plate cir-cuit of the tube in usual manner. Theadvantages are greater volume and betterquality. The pick-up works more effec-tively into the grid circuit 'of the tubethan into the primary of a transformer,and the primary of the transformer ismore effective both as to quality and vol-ume when it is connected to the plate cir-cuit of the tube than when it is connectedto the pick-up.

LAYOUT FOR S -M 250 UNIPAC

coils insures close inductive coupling be-tween the primary and the secondary andat the same time keeps the capacitycoupling down to extremely small values.These factors are consistent with highselectivity and extreme sensitivity, andthey largely account for the popularityand performance of these ci,rcuits.,

The regenerative feature in the detec-tor builds up the selectivity to a pointcomparable to that obtained in circuitthat have miniature primaries and smallamplification. Thus with a screen gridtube, a high impedance primary and witha regenerative detector it is possible toattain almost unbelievable amplificationwithout in the least sacrificing selectivity.Thus a circuit like the Browning -Drakeis greatly improved.

Proper location of coils is assured byemploying the National kit, in which thecoils, condensers and the dial are mountedon a frame as a unit. The coils are atthe extreme ends of this assembly so thatcapacity coupling is negligible. The coilsare also placed at right angles so that theinductive coupling between them is nil.

One Control

The two condensers are control by thesame drum dial, making the circuit sin-gle control. To compensate for the differ-ence between the input capacities of thescreen grid tube and the -01A tube a.0001 mfd, condenser is connected inparallel with the condenser which tunesthe first tuned circuit. Thus the two cir-cuits are Made practically identical.

For compensating for the effect of theantenna on the first tuned circuit an in-ductive trimmer is used. This is a smallrotor in inductive relation with the firsttuning coil, with which it is connected inseries. Thus no loss of selectivity resultsfrom the use of a common tuning control.

Since 'a screen grid tube has only anegligible capacity between the plate andthe control grid frequency amplifier willnot oscillate when the regeneration in thedetector is turned up. In fact the regen-eration in the detector makes the RF am-plifier work a greater efficiency as regardsvoltage amplification, but this is regularamplification and not regenerative.

Set Does Not Radiate

When tuning in distant stations it ispermssible to use the squeal method forthe circuit will not radiate. The screengrid tube prevents the oscillation fromreaching the antenna, where they wouldbe radiated. The small size of the threecircuit tuner and its vertical placementstill further limit radiation from the ch.=cuit while oscillating.

The circuit is very simple to build dueto the fact that the essential kit is alreadyassembled in one unit and no neutraliz-ing or shielding is necessary. There isnot much to do but mount the socketsand the audio amplifier.

The audio amplifier in the receiver isdesigned for high quality reproduction andstability. Three different National Imped-aformers are used, each specially designedfor the position it is to occupy. The firstis designed to take the output of a -71A.detector efficienctly, the second to workbetween a -40 type tube and a -71A.Careful attention has been given to con-tributory causes of motorboating when thecircuit is operated with a B battery elim-inator in designing these audio couplers.

[James Millen will describe the construc-tion of the National Shield Grid Five innext sc'eek's issue, April 14.]

April 7, 1928 RADIO WORLD

Electric Brain a SuccessMachine Transforms Speech

to Gibberish Then Trans-lates It-Permits Secrecyin Transmission-Workson Distortion Principle-Artificial Larynx, AnotherInvention, Permits Someof Dumb to Talk Again-Deaf Aided.

STRANGE languages synthetically manu-factured, and spoken by no human

beings, issued from the horns of the loud-speakers in the United States EngineeringAuditorium, 29 West 39th Street, NewYork City, during the talk and demonstra-tions of Sergius P. Grace, general com-mercial engineer of Bell Telephone Labora-tories, who was telling the members of theNew York Electrical Society about a fewof the marvelous scientific accomplishmentsof the Laboratories.

Mr. Grace explained that in connectionwith radio transmission systems designed tomake radio conversations secret, there hadbeen developed methods of inverting anddistorting the natural speech frequencies,or tones, so as to make the transmittedspeech unintelligible to the ordinary radiolistener.

Mr. Grace had with him phonographicrecords of such inverted speech in whichthe natural high frequencies had been trans-formed into low frequencies and vice versa.

Manufacturers GibberishWhen a record of this kind was played

by Mr. Grace on a Victrola there issuedfrom the horn a form of synthetic speechwhich was absolutely unintelligible to theaudience, but in which there were retained,nevertheless, all the original frequencies,or tones, in the voice of the person makingthe record, but with these frequencies re-versed.

The resulting language was somethinglike an imaginary mixture of English,French, Chinese, Siamese and a few otherlanguages thrown in for good measure. Ifwe had been accustomed from childhood tosuch a language, we would understand it,Mr. Grace said. Then Mr. Grace startledhis audience when he told them he hadbrought with him from the Laboratories amachine with "electrical ears" and an "elec-trical brain," which could understand thisunintelligible gibberish and retransform itinto its original language.

The audience of 1,000 members of theNew York Electrical Society and guestswaited in suspense while he proceeded todemonstrate this modern "Babel" trans-lator.

Electrical Brain at WorkWhile the unintelligible speech was issu-

ing from the Victrola, Mr. Grace held infront of the horn an electrical pick-up trans-mitter similar to the transmitters used inradio broadcasting studios. The electricalcurrent from this transmitter was carriedinto the "electrical translating brain," thenamplified and connected with the loud-speakers of the public address system whichhad been installed in the auditorium.

Immediately, these loudspeaking hornsburst forth at a volume several timeslouder than the phcinograph, with the orig-inal speech in English and, clearly under-standable by all the audience. Whenever

SERGIUS P. GRACE, GENERAL COMMERCIAL ENGINEER, BELL TELE-PHONE LABORATORIES, DEMONSTRATING THE ELECTRICAL EQUIP-MENT DEVELOPED BY THE LABORATORIES, WHICH TURNS SPEECHINTO GIBBERISH AND BACK AGAIN, AT THE MEETING OF THE NEWYORK ELECTRICAL SOCIETY, ENGINEERING AUDITORIUM, 29 WEST 39TH

STREET, NEW YORK CITY.

Mr. Grace would move the pick-up trans-mitter, or "electrical ear, away from thephonograph, the sound from the loudspeak-ers would cease and the audience wouldagain hear the unintelligible gibberish issu-ing from the phonograph.

Curiously enough, although at all timesthe synthetic speech was being transmittedinto the room, whenever the loudspeakersconnected with the electrical translationsystem were in operation, the translatedspeech sounds over -rode entirely the phono-graph gibberish. Thus we have added tothe marvels of science an electrical machinethat can understand a language unintelli-gible to ordinary human beings.

Chance for Secret LanguageTo demonstrate his ability to speak some

of this new synthetic language, Mr. Gracehimself spoke into the transmitter the cryp-tic words "Play -a -fine Crink-a-nope" which,after translation by the machine, came outof the loudspeakers as "Telephone Com-pany." In this way, Mr. Grace pointedout, it would be possible to build up a newlanguage from an old one, with the indivi-dual words inverted so as normally to benot understandable.

Mr. Grace during his talk about otherproducts, he described the functions of theloading coil and telephone repeater, andgave brief descriptions of television andradio trans -Atlantic telephony, both recentaccomplishments of the Laboratories' staff.

Mr. Grace also pointed out that much asthe research work of the Laboratories hadproved of value from purely a humanitarianpoint of view. In particular, he describedand demonstrated the Artificial Larynx, aproduct of the Laboratories which enablespeople who have lost their larynges throughsurgical operations to talk again.

Deaf Are AidedAnother most interesting contribution to

humanity is the new telephone receiver de-

veloped by the Laboratories for teachingthe deaf. This device has five miniatureindividual receivers with contact pins uponwhich the deaf person places his thumb andfingers. The incoming electrical currentfrom the transmitter of the teaching instruc-tor is electrically filtered into five fre-quency bands suited to each receiver andthus, whenever a particular word is spoken,there is a definite rhythm or sequence ofthe vibrations in the five receivers in con-tact with the fingers of the hand.

The deaf person soon learns the "pattern,"so to speak, of each individual word andin some cases is able to acquire a very con-siderable vocabulary in a short time. Thismethod of instruction was conceived and isbeing used by Dr. Robert FL Gault in Wash-ington under the auspices of the NationalResearch Council, the apparatus being builtfor him by the Bell Telephone Laboratories.

Penn ManufacturesBrielle Balanced Unit

The i;-. Balanced Armaturea new driving unit for any type con:,cloth or wood diagram speaker, is nowon the market and is finding favor. Tbisis a sturdy unit, well designed and pos-sessing unusual mechanical features. Theparts, while well protected, are readilyaccessible. Among the improvemen.:.unique in this motor are direct magneticpath, broad pole face and armature oflarge effective surface assure maximt.rnaction on armature, it handles output ofmodern power packs direct through coilsno output transformer being required.

This motor is put out by the G. R.Penn Manufacturing Co 34 West 3rdStreet, New York City. Full informationmay be had from them by mentioningRADIO. WORLD.-J.H.C.


A Good Mixer in the

FIG. IIN A AND B THE SAME OSCILLATOR HOOKUP IS SHOWN, THE PLATE COIL IN B BEING PROPERLYDIAGRAMMED IN INDUCTIVE RELATIONSHIP TO THE GRID COIL. A DIFFERENT TYPE OF OSCILLATOR,WITH THE GRID TUNED, IS SHOWN IN C. AN UNUSUAL METHOD OF COUPLING THE OSCILLATOR TO THEMODULATOR IS SHOWN IN D, WHERE THE CONDENSER RS IS ALSO USED AS A SELECTIVE VOLUME CONTROL.

MANY interesting possibilities presentthemselves when one seeks the con-

struction of a suitable mixer for a Super -Heterodyne.

Nearly all of the methods used in stand-ard Super -Heterodyne kits are good.Some are better in one respect than in an-other, but the designers simply choose thehookup that gives them what they deemthe most desirable compromise.

At every point in radio design com-promise enters. Your engineering knowl-edge is no better than your ability tocompromise, whether that compromise bebetween selectivity and quality, sensitivityand stability, volume and undistortedpower output, simplicity and efficiency orbetween economy and performance.

In the Super -Heterodyne mixer itself

80

70

60

.50

40

30

20

/0

0

the selectivity factor enters only at a pre-ventive of secondary interference. Thisis the greatest source of audible beatnotes, whistles, gurgles and squeals, andis due largely to the inability of the tuneror first detector to discriminate in favorof the desired frequency against all others.Hence as a palliative one many includeregeneration in the first detector, or mayprecede a straight detector with a stageof frequency amplification, amethod which makes tuning easier thanby the regenerative method.

The Unusual DetectionIn Fig. 1A is shown a familiar mixer,

consisting of the tuner or first detector(1) and the oscillator (2). The first de-tector does not detect for the usual pur-

MaMIIMMEMMEMMEMMEMMMEMMaalimalaMMEMEMMIMMaanMaim mammilummarnilimilmmiMalliMmmemmmammilMMEMMNEmiamilaMMIIMMMEMMINEMNIMMEMOMENEMMEMaMMEMIrninniaMMEaMMENEMEMimminmammilimmimmilmammumwasamma.=. ... :z=mamil mmmmm mamainammanlimaMMEMMEMICIMMEMMEOPradrnanOMOMMONOAMMEMMEMMOalliMEMEMMEMEMMEMEMMMMUMNEnammaimmmamomaaMMININNEMMEMMEMMIMMIIMMUMEMMEMMEM mm mm MMEMEMEMMEMEMEMMEMEM:NMMEMOMMEMIMEMMEMMESEMMEMEMIWAMMEMMENEMaamminimalliMMEMI.IMOMMmainammommuMmammilmaaraalimilmamammaMmiumummaimilliMaZallalliMMOMMEMEMEMEMMEMPAMEMEMOUMMIIMMEMMUMEMMEMMErnmmil0manimmaimallimaMMIMPIIMMEMMarnimMEMOMEMMEMEMENMEINOMMMEMEMMENOMMEMEMOMMEMMOMMMEMEMEMMEMMESMEMMEMMEMONMEMMEnn

AMEMMEMEMMEMMUMWAMMEMEMMINNEMEMUMMOMMEMENEMMEMINMEUXIIMMIIIMMOMMEMMEMMAng AniMiNIUMMEMEMOMMEMEMEMOMMEMOMMEMEMMEMNMEMEMMILIMMEMENUMMEMEMMEMMMEMMOMMEMEMNIMOMMEMMUMMinmommilammilammaramaimmilaMMMEMMmilliaMMEMIMOMMINUMMUMMOMEMMEMIMMEMMAMEMEMIIMENMEMMIrnallimmommiaMMEMEMMEMMEMEMONIMEMEMEMMilainllEMMEMMINIMMMONEMESEENIINEMMEMMEMOMIEMMMMM amaamomirammommommmommommam maw MMMMMUmammanummAannimmil mamma MMMMM MMMMM MMMMMMM mayMEMMUMNEMOUMEMMEMEMMEMMEMEMENImmulimilMmamMMMOMMUMMEMImmammilammmilammammamilrnamalimMilirnmmommrnaammmillinmaimmaimadmamm MMMMM Emu MMMMM maammosamimaamaimmMMMMM MEMMEMUMWENEMEMMEMEMIMMEMMEMMMERMEMMEMMEMMMOMMENMEMMMallialiNarAMMIMMUMMEMMOOMMEMMUMMIUMMOMMOMMEMOMOMMEMMIMillaiMMWOMManaMMEMMaillaillaaMMEMMEMEMOMMEMEMMEMMEMMOMMEEM

MMMMMMMMMMMMMMMMMMMM amammilimanmsrnaarnsimulammamalumanammimaamilmmamammomm MMMMM a MMMMMMMMMMMMMMMMMMMMamaarAMMIMIMMallimairnialiNEMNEMMUMEMMINIONMMEmmmammommmininMraMOMMENEMMENEMMEMMINIMMilmallaillmmillninaliMMEMEMERMIUMMamannalimmialmilmimmamilmilimmainimmimmammammummumilammmoWimmaimmailmaalmammilaiMMEEMammmalaimminnmEmmommommarnilmammammallinalrEMMENIMMMEMMIllammillaimmarnammalawmaMIMOMMUMMOMMIMIMMOMOMMEMMEMMOMMOMMEMOMIIMMOMEMMOMMINIImmo MMMMMM immummialammaamamminarnimilmmaMmilimmiallOMMMEMEMMEMMOMMEMMEMMOMMEMMIUMMENUMMIIMMEMOMEMMOMMEMMINEillaanEMMEMMOMMEMMENEMOMMIMMErnmairammmemmommommingam

OO

O OOO

OOO

OO

OO

OO

co

OO

OO O

co

FIG. 2

CURVE SHOWING HOW THE COUPLING CONDENSER CAPACITY AFFECTSVOLUME. INCIDENTALLY, AS THE VOLUME IS DECREASED THE

SELECTIVITY IS INCREASED AUTOMATICALLY,

pose, that is, to produce audible signals,but detects by receiving a higher radiofrequency and, through modulation, de-livering a lower, but still radio, frequency,still inaudible. That lower frequency isknown as the intermediate frequency andis produced by the mixing of the stationfrequency with the oscillator frequency.The mixing place is tube (1) and is knowntechnically as modulation.

The tuning condenser connected be-tween plate and grid of the oscillator,with stator S to grid, in conjunction withthe secondary L4, governs the oscillatorfrequency. Note that L5 is shown to theright, as is usual in such diagrams, al-though in fact this plate coil is always ininductive relationship to the primary L3(the pickup coil) and particularly the sec-ondary L4, hence the diagram in Fig. 1Bshows the real situation accurately inrespect to L5.

Instead of placing the oscillator tuningcondenser from grid to plate, thus tuningboth those circuits at once, one may tuneonly the secondary. This requires moreturns on the plate coil 1.5 (Fig. 1C), be-cause the coupling is exclusively inductive,save for some tiny capacity coupling dueto the distributed capacity of the coilwindings and to a possible radio fre-quency potential difference between thephysically adjoining terminals of the platecoil and the grid coil.

Body Capacity

The method shown in C is .a good one.The oscillation is no better than in theother instance, indeed, due to insufficientplate coil inductance, some coils might beused in this fashion without producingany signals in the loudspeaker, or wherebyfailing to produce them at the lower,broadcast frequencies (higher wave-lengths) at which the plate coil might failto produce oscillation.

On the other hand granting oscillation,one has a greater latitude in choice oftypes of tuning condensers, since one sideof the tuned circuit is at ground potential,and the rotor is connected to this point.The condenser stator S goes to grid.

Absence of body capacity is more easilyattained by this method, because in Fig.1A and Fig. 1B both the high radiofrequency potentials of two coils in oneoscillating circuit go to the tuning con-denser. By proper design, excellentchoice of condensers and wise location ofparts, body capacity may be greatly re-

April 7, 1928 RADIO WORLD 11

Aristocracy of Circuitsduced or prevented, even when the grid -to -plate method, or Hartley oscillator, isused, but with the other design it is fareasier to avoid body capacity.

If the reactance of the plate coil is nothigh enough at a low broadcast frequencyto induce oscillation, a fixed condenseracross it may help (Fig. 1D, dotted lines).However, in any event a rotary ticklercoil, as in conventional three circuit tun-ers, will produce oscillation over the en-tire wave band when the plate coil istightly coupled to the grid coil. Thetickler is set once and left thus, henceneed not be panel mounted.

Rare MethodWhereas a pickup coil of few turns was

used in the previously cited instances, inFig. 1D another and rare method of coup-ling is shown: The object of any form isto link the oscillator and the first detectorcircuits. In the coil method the grid sys-tem of modulation was used, that is, theoscillator's generation was induced in thegrid circuit of the first detector bymutually inductive coupling.

In Fig. ID the capacity method of coup-ling is used, and number of windings inthe oscillator system is two, instead ofthree. There is no pickup winding. Thecondenser RS couples the circuits se-lectively.

It will be seen, therefore, that two radiofrequency transformers or antenna coilsof the same characteristics might be used,provided the primaries are large; or, ifsmall, the primary on the coil to be usedin the oscillator circuit would be en-larged and the other primary left as it is.About 35 turns on a 3 inch diameter, usingNo. 24 single silk covered wire, would besufficient winding for L4, whereas theother windings might be 50 -turn second-aries and a 10 -turn primary (L1).

At Same RF PotentialBody capacity effects will not be noticed

in the condenser method of coupling, be-cause there is no essential potential differ-ence between the two points of connection,the plates of the two tubes, nor is eitherin a very critical state, anyway.

Any selective method of coupling is onewhere the coupling is adjustable from avery low limit to as high a degree as ispractical or desirable.

In this connection the capacity of thecoupling condenser is important. It wasfound that with coils wound of No. 24single silk wire on the three inch diam-eters that and with -01A tubes for os-cillator and modulator, terminals of thecoils being connected in the same relativeorder to avoid phase shifting,] beyond.0005 mfd, an increase in capacity had athrottling effect, diminishing volume,where as from minimum capacity settingof the coupling condenser up to .00035

tthe variation was not only smooth' butfrom faintest reception, just enough forearphone use, to powerful sound sufficientto be heard two blocks away.

This was a range with a vengeance,hence the coupling condenser was 'se-lective of degrees of volume, and accom-plished this work very nicely while in-creasing the actual selectivity when vol-ume was lowered.

By-pass CondensersThis is exactly as it should be, since the

loudest stations we receive have a greaterdial spread than the weaker ones, and theselective method of coupling reduces thedial spread about proportionally to the

0

GC

AMP

8 DET.

R -8 -

FIG. 3

A STAGE OF TUNED RADIO FREQUENCY AMPLIFICATION AHEAD OF THEFIRST DETECTOR, PLUS A VARIABLE CAPACITY COUPLING BETWEENOSCILLATOR AND MODULATOR, FOR SELECTIVE VOLUME CONTROL. IFTHE TRF AND FIRST DETECTOR TUNING CONDENSERS ARE GANGED,AND HAVEN'T TOALLY INSULATED ROTORS AS WELL AS TOTALLYINSULATED STATORS, THEN THE LEFT-HAND CONNECTION OF THEGRID LEAK SHOULD BE MADE TO A PLUS DIRECT, INSTEAD OF TO THE

GRID 'COIL. THIS REQUIRES A SEPARATE LEAK MOUNTING.

decrease in volume. This is not alwaystrue of other forms of volume control, forthese often leave selectivity where they -find it, and merely reduce volume.

As we are progressing toward a tunerand oscillator of certain design it is wellto note another point of difference in Fig.ID. A lone bypass condenser BC, sayabout 1 mfd., between A minus and B plus,was all we discovered previously, but nowappear three more, two of them acrossthe Amperites, and the third from fila-ment minus of the modulator to B' plus.Note, too, that the common point is madethe negative filament in each tube. Thisis supported by the general use of nega-tive filament in determining grid bias andindeed in making all static reckonings inrespect to vacuum tubes. Also it is themost likely place to be put at groundpotential, since it marks the end of_ thedesired radio circuit for that

Bypass ReasonThe reason for bypassing the resistor is

to render the circuit as stable as can be,and to negative so far as possible the

0Input

O

T.R.F.

FirstDet.

- 0 sc.

effect of the plate current passing throughthe filament. While a bypass condenseracross any filament resistor does not affectthe direct plate current, it does detour theAC component or radio frequency cur-rent in the plate 'circuit and minimize thecommon coupling introduced by the unisonof filament and plate current in this re-sistor, which otherwise produces smallvalues of feedback.

The fact that the direct plate currentflows partly through the filament resistoris often overlooked, but the plate currentfrom the B supply is delivered to theplate, is conducted past the grid to thetube filament through the space path in-side the tube, and divides unequally inboth legs of the filament, one of whichwears as a protective legging the filamentresistor.

Constructors will say that, testing sucha circuit with the' filament resistor bypasscondensers in and out, they do not noticeany difference. Neither do they noticeany difference in time between a thou-sand -dollar watch and a dollar watch,when they simply look at both for a

Int. Second.Det. Audio

OOutput

0

FIG. 4

THE ELECTRICAL ORDER OF THE CIRCUITS SHOWN IN FIG, 3. THE TRFSTAGE FEEDS INTO THE FIRST DETECTOR, TO WHICH THE OSCILLATORIS COUPLED. THE COMBINED RESULT IS DELIVERED TO THE INTER-MEDIATE AMPLIFIER, WHICH IMPRESSES THE GREATLY AMPLIFIEDINTERMEDIATE CARRIER UPON THE SECOND DETECTOR, AFTER WHICH

THE AUDIO CHANNEL DOES THE REST.


Sok

IN

C3

T,

CDO

A Super for

TZ T3 T4 Ts

By Bramhall

SPEAHER0

0 as 0 H+4S.

Ob-C.) A -

A 5 -CJ.

THE CIRCUIT DIAGRAM OF A SUPER -HETERODYNE SUITABLE FOR A TRANSPORTABLE RECEIVER LIKE THATMADE BY SEYMOUR SAGER. REGENERATION IS USED IN THE FIRST DETECTOR.

HERE is a transportable receiver ratherthan a portable one, excellent for in-

stallation in an automobile. It is too heavyto be carri'd suit -case fashion but is of asize that permits mounting on the instrumentboard of the car.

The automobile receiver, like the portable,must be sensitive enough to pick up signalswherever the automobile may be, and thatoften is in places where ultra -sensitivity isrequired. The receiver therefore is naturallyof the Super -Heterodyne type.

It contains eight tubes, which in a cor-rectly designed receiver of this type willgive sufficient sensitivity for all 'reasonablerequirements.

Ruggedness a Requisite

A receiver designed for constant use inan automobile must have certain character-istics not required of small portable receiversor of home receivers.

The first is that of unusual ruggedness.It must be built to withstand all the joltsand vibrations to which it will be subjectedin an automobile which may travel fast overrough roads.

The structure of the set must be sturdyand well braced so that there will be a mini-mum of play between the parts.

All nuts used for holding parts togethermust be locked either with lock washers orin some other positive manner.

Special attention must be given the mount,ing of, the tubes. Ordinarily the ordinarysockets, either the push or the bayonet types,are not dependable. as the tubes are likelyto be shaken out of either type in time. Ofthe two types, perhaps the bayonet type isthe more reliable ,particularly when used fortubes mounted upside down, as many of thetubes are in this "automobile" set.

Many methods of locking the tubes inplace will suggest themselves to the builderof such a set. For example, rubber bandscan be used to hold the tubes in place, ortwine may be used for the same purpose.For more or less permanent tubes plasticwood or a suitable cement can be used forfastening them in their sockets.

If the tubes are not mounted securely theywill fall out of their sockets, and as thiswill happen when the car is in motion, theprobability of breakage of tubes then wouldbe high.

Individual Design

It would not be practical to give the exactdetails of the receiver built for a particularcar, for the design that fits that car maynot necessarily fit any other car. A meresuggestion to the ingenious radio fan andautomobilist will suffice.

The photographs of the set built and de-signed by Seymour Sager, 92 Carrick Ave.South, Hamilton, Ontario, Can., show thathis eight -tube Super -Heterodyne is a typeof double-decker. It has only one deck butparts are mounted both above and below it.Thus some of the tubes and transformersare mounted right side up and others aremounted upside down.

The panel of the receiver is a square 11inches on a side. The sub -panel partition ismade of wood thick enough to allow mount-ing of parts on both sides with wood screwswithout mutual interference. The arrange-ment of the parts on the panel can be seenon the photograph of the automobile instru-ment board.

A filament circuit voltmeter of diminutivesize is mounted in the center near the upperedge. Below are the two tuning controls,which are General Radio vernier type con-densers. The various volume controls aredistributed on the lower two-thirds of thepanel.

Placements of Parts

The radio frequency portions of the cir-cuit are placed on top of the baseboard whilethe intermediate and audio frequency partsare mounted under it. A good idea of howthis is done is gained from the upper leftand right photographs.

The loudspeaker, consisting of the drivingunit and a large horn, is placed under thehood of the car beside the engine. Themanner of placement is shown in the lowerleft photograph. By comparing this photo-graph and that of the instrument board it isapparent that the -loud speaker is placed di-rectly behind the receiver viewed from thedrivers seat.

The filament power is derived from theautomobile battery, while the B power isderived from a set of dry cell batteries andthe C voltage from a small dry cell batterymounted in the upper compartment in thereceiver.

Loop Operated

The receiver is loop operated, as befits aSuper -Heterodyne and a transportable set.The loop is placed in the car over the driver,and is so mounted that it can be raised orlowered as suits the purpose of the operator.

Mr. Sager, the designer and builder of theset, took 11 months to iron out all the kinkifrom the set, and to get it working properlywhile the car was running at high speed. Hisgreatest difficulty was in holding the tubesin place. No less than 4 dozen tubes werelost before this trouble was overcome. Notethat the sockets used are of the bayonet type

Sockets of this type are used for electriclights in all trains, cars and boats becausethey hold the lamps.

Sensitivity of Set

When the cards motionless and the enginenot running stations within a 1,500 mileradius come in regularly with loud speakervolume, and often more distant stationscome in with similar volume. While trav-eling at a speed of from 30 to 40 miles anhour stations within a radio of 500 milescan be heard distinctly. Thus while tray -

LIST OF PARTS

L-One loop to tune with a .0005 mfd.condenser.

LI, L2, L3-0scillator coupler to tunewith a .0005 mfd. condenser.

T1, T2, T3, T4-Four Silver -MarshallNo. 210 intermediate frequency trans-formers.

T5, T6-Two Thordarson R-200 audiotransformers.CO, C5-Two Carter .00025 mfd. grid con-densers with grid leak clips.

CI, C2-Two General Radio verniertype .0005 condensers.

03-One General Radio 100 mmfd.midget condenser.

C4-One Carter I mfd. by-pass con-denser.

C6-One Carter .001 mfd. by-pass con-denser.

IA-Five No. IA Amperites.Rhl-One Frost 20 ohm rheostat.Rh2S-One Frost 10 ohm rheostat with

filament switch attached.RI, R2-Two Durham 2 megohm

leak.Pl-One Frost 400 ohm potentiometer.P2-One Centralab 500,000 ohm modu-

lator.Eight bayonet type (old) sockets, spring

suspension.One 0-6 volt panel mounting "Double

R" voltmeter.Two General Radio Bakelite type

vernier dials.Two Carter Imp jacks.Seven Eby binding josts.One 11 x 11 inch Cortlandt panel.One wooden sub -panel.Seven 01A tubes and one 112A tube.Three 45 volt B batteries.One 7,/ volt' grid battery.One loudspeaker.One automobile.

grid


Your AutoTorrence

UPPER LEFT-LEFT VIEW OF THE 8 -TUBE SUPER -HETERODYNE OF SEYMOUR SAGER, SHOWING THEOSCILLATOR AND THE INTERMEDIATE TRANSFORMERS. TOP CENTER-INTERIOR OF THE AUTOMOBILESHOWING HOW THE RECEIVER IS INSTALLED ON THE INSTRUMENT BOARD. UPPER RIGHT-REAR VIEWOF THE RECEIVER WHICH SHOWS THE DOUBLE DECK CONSTRUCTION. LOWER LEFT-THE LOUDSPEAKER IS INSTALLED UNDER THE HOOD OF THE CAR AS SHOWN HERE. LOWER RIGHT-MR. SAGER

HIMSELF AND HIS RADIO -EQUIPPED CAR.

eling at that rate at a distance of 500 milesfrom New York it is easy to follow aspeaker from the New York stations.

Mr. Sager, whose home is in Hamilton,Ontario, listened in to the Tunney-Dempseyfight direct from station WLS while he wasseated in his car near New York.

The difference between the stand -still andthe running sensitivity is due to inter-ference from the engine. The sparking canbe heard and becomes objectionable whenthe sensitivity is turned up toward its max-imum. But it speaks well for both the carand the receiver that the interference is notany more troublesome than it is.

Selectivity

The selectivity is enough for the range ofthe set. No interference from stations near-by is experienced when listening to thefarthest receivable stations even when thefrequency separation is small.

A suitable circuit diagram for a receiverof this kind is shown in Fig. 2. This showsthat regeneration is employed in the loop.This is a very useful feature in any port-able set where sensitivity is required, aswell as for suppressing certain squealswhich may at times be present unless theradio frequency selectivity is high as wellas that of the intermediate frequency.

The regeneration is controlled by meansof a 100 mfd. midget condenser C3. Thisis the first volume control aside from thetuning controls.

Volume Controls

There are four additional controls of thevolume. One is the 20 ohm rheostat Rhlin the negative lead to the modulator tube.The next is the 10 ohm rheostat Rh2 inthe negative filament lead to the first twointermediate tubes. The fourth is the 400ohm potentiometer P1 across the filamentcircuit to which the grid returns of the threeintermediate amplifiers are connected. Thesetwo controls, that is, Rh2 and P1, controlthe amplification and the oscillation in theintermediate amplifier.

The fifth volume control is the half meg-ohm potentiometer P2 across the secondaryof the first audio transformer.

The oscillator is of the tuned grid type.which is used because of the absence ofbody capacity.

The filament current in all those tubeswhich are not controlled by rheostats islimited by means of Amperites. One ofthese is used for each tube. Since all thetubes in the circuit are either of the 01A orthe 112A type all the Amperites are No. 1A.Only the last tube is a 112A.

Detection and Modulation

The modulation is accomplished by meansof the grid and condenser method. The gridcondenser CO is of .00025 mfd. capacity andthe grid leak across it is 2 megohms. Acondenser as small as .0001 mfd may beused here if desired.

The detection is done by the same method.

The capacity of condenser CS is .00025 mfd.and the resistance R2 across is also 2 meg-ohms. Of course the grid returns of boththe modulator and the detector go to thepositive end of the filament.

Both of the tuning condensers Cl and C2are General Radio .0005 mfd. vernier typecondensers. The loop must be designed tothis size condenser and it should be tappedat the center turn. The oscillator coupleralso should be wound for the .0005 mfdcondenser. The pick-up coil L3 may wellbe mounted so that its coupling with L2can be varied. But it is not desirable tohave a knob for this variable on the panel,for it affects the.

M. is the filament voltmeter. S is thefilament switch, which should be incorpor-ated in one of the volume control rheostats,Rh2 for example.

Ti, T2, T3 and T4 are intermediatefrequency transformers while T5 and T6 areaudio frequency transformers.

The oscillator coil and pickup can bemade easily by the constructor. On a3 -in. diameter the secondary 12 shouldconsist of 43 turns of No. 24 magnetwire. The plate winding Ll may consistof 30 turns of the same wire, or finerwire if available. The pick-up coil L2may have from ten to fifteen turns. Thelarger number gives slightly greater sen-sitivity but correspondingly lower selec-tivity. If an old three circuit tuner is re-wound for the job the pick-up coil shouldbe put on the rotor so that the pickup canbe varied as desired.

14 RADIO WORLD April 7. 1926

Double Modulation

THE CIRCUIT DIAGRAM OF AN EXPERIMENTAL HOOK-UP FOR DOUBLEMODULATION. THE MODULATED CARRIERS FROM THREE DIFFERENTBROADCASTING STATIONS ARE IMPRESSED ON THE MODULATOR OF

A HIGH FREQUENCY TRANSMITTER.

By Brunsten BrunnTHE new plan involving double modu-

lation and transmission on high fre-quencies outlined by J. E. Anderson,Technical Editor, in RADIO WORLD March17 has attracted considerable attentionboth in technical and lay circles, due tothe promise which the system holds outto those who would like to broadcastcannot find room in the present broad-cast band and to those listeners whowould like a greater practical latitude intheir choice of broadcast entertainment.

Let us review the theory. As a firststep consider what occurs when a broad-casting station transmits a given musicalnote. Let us further confine our atten-tion to a broadcast frequency of 1,000kc or 300 meters, and to a pure tone ormusical frequency of 1,000 cycles per sec-ond. This frequency is a little lower thanthe C two octaves above middle C.

Modulation or MixingWhen the 1,000 cycle note is sounded

before the microphone in the studio anelectric current of 1,000 cycles per sec-ond is produced in the modulator circuit.This current is amplified and ultimately

mixed with the 1,000 kc radio frequencyof the transmitting oscillator.

The mixing or modulation is not asimple process and the result of it is nosimpler. But for practical purposes wecan say that the product of the modula-tion consists of four different compon-

is the 1,000 kc radio fre-quency current of the oscillator, which isknown as the carrier. The second is aradio frequency current the frequency ofwhich is the sum of the oscillator fre-quency and of the 1,000 cycle note im-pressed on the carrier. In this case thisfrequency is 1,001 kc.

The third component is a radio fre-quency current the frequency of whichis the difference between the oscillatorfrequency and the 1,000 cycle note im-pressed on the carrier. In this case thisfrequency has a value of 999 kc.

The fourth component in the modulatedwave is a current the frequency of whichis that of the 1,000 cycle note impressedon the carrier.

Although the purpose of the entiretransmission is to convey the 1,000 cyclemusical note to listeners at the receivers

New R.C.A. EliminatorIs Dry and Tubeless

A B eliminator which marks a departurein socket power devices was announcedby the Radio Corporation of America.The new device, according to its sponsors,is designed to meet the demand for areliable and efficient B or plate supplyrequiring minimum attention and main-tenance expense.

The new eliminator, which will beknown as Model AP -1080, is of ruggedconstruction, and employs no acids orliquids to be replenished; it has nomechanical parts or tubes to be replaced.The secret operating mechanism is en-closed and sealed in permanent steel con-tainers. It is extremely compact, measur-ing 7i by 10 by 6% inches high andwill readily fit into the usual radio

cabinet. When the new eliminator is con-nected to the lighting socket and radioset, it requires no further care or atten-tion.

The operating cost is low. The devicedraws 22 watts under average load. Thepower output is ample for any type ofreceiver up to the eight -tube circuit withpower tube. The maximum voltage hasbeen limited to 135, since for all practicalpurposes in the average home the loud-speaker volume of a -71 or -71A, whenused with a plate voltage of 135, will givethe same satisfactory results as when themaximum allowable potential of 180 isapplied. Furthermore, at the lower platevoltage the life of the power tube is ma-terially prolonged.

tuned in on the transmitting station, weare not at all interested in the current of1,000 cycle frequency. It is not trans-mitted.

Transmitted TrioBut we are very much interested in

the three other components: All these areradio frequency currents and have thefrequencies 999, 1,000 and 1,001 kc. Themiddle is the carrier and the others arethe lower and upper side frequencies, re-spectively. The transmitting antennaradiates all of these in the form of elec-tro-magnetic waves.

And every receiver tuned in on thestation receives all of these. Althoughevery receiver is tuned nominally to thecarrier frequency only, it also receives theside frequencies. This is possible be-cause no tuner is perfectly selective. Ifit were, telephone reception would be im-possible.

The three radio frequencies picked upare amplified and finally impressed on thedetector or _demodulator.

Dernodulation or DetectionThe product of the detector or de-

modulator is a highly complex electriccurrent. It contains one component inwhich we. are much interested, and thatis a current having the same frequencyas the musical note that was sounded be-fore the microphone. The' transmitterrejected this, but in the receiver that isthe only one that is finally desired. It iscarefully nurtured and amplified in a re-gular receiving set until it has the desiredmagnitude, when it is turned into theloudspeaker. The energy contained in,this current comes out of the loudspeakeras a musical note, a close reproductionof the note that was sounded before themicrophone.

Thus the musical note we selected,namely 1,000 cycles, has been carried byradio waves across the space betweenthe transmitter and the receiver andfinally reproduced as sound.

Other musical frequencies are carriedand reproduced in the same way. Andmany different musical frequencies andother sounds can be carried and repro-duced simultaneously.

The frequency of the carrier of all ofthese is the same, namely 1,000 kc. Butthe side frequencies differ. For a tone of100 cycles the three frequencies are 999.91,000 and 1000.1 kc. For a 10,000 cyclesound they are 990, 1,000 and 1010 kc.

Frequencies Not LimitedIn broadcasting even the highest audio

frequency impressed on the radio fre-quency carrier is very low as comparedto the carrier frequency. But there is nofrequency limit to two frequencies thatmay be mixed. The two may be equal, inwhich case one side frequency is zeroand the other is twice that of either, i.e.,the sum of the two. As one of the inter -modulating frequencies is varied and thetwo are brought to equality the lowe,side frequency approaches zero throughthe entire audio scale. That is the hetero-dyne squeal which can be heard in alloscillating sets.

The frequency impressed on a carrierfrequency can thus have any value, atleast from zero up to the value of thecarrier frequency. And the carrier canhave any frequency we choose.

High Frequency ChosenLO us therefore choose a carrier fre-

quency of 20,000 kc, twenty times as highas the radio frequency carrier we con-


Producible in Homesidered before. We can modulate thishigh carrier with any frequency wechoose. Then we can modulate it with aradio frequency of 1,000 kc. The mainproducts of the modulation will be thefour frequencies 19,000, 20,000, 21,000 and1,000 kc. Just as we rejected the 1,000cycle frequency in broadcasting so wenow reject the 1,000 kc frequency in thiscase. The two side frequencies and the20,000 kc carrier are radiated.

Shortwave Receiver UsedNow a short-wave receiver can bring

in the 20,000 kc carrier and the two sidefrequencies, 19,000 and 21,000 kc. Thetuner should not be too sharp or the sidefrequencies will be suppressed too much.

If these three frequencies are receivedand impressed on a detector or a modu-lator the 1,000 kc frequency previouslyrejected will be reproduced. ' Beyond thedetector this is the only frequency we areinterested in for the moment, and we tunefor it. We tune for it just as we wouldfor a broadcast frequency of 1,000 kcand we can use the broadcast receiver.

Thus the 1,000 kc radio frequency nasbeen carried through the space interven-ing between the transmitter and the re-ceiver on a radio frequency of 20,000 kc,-and it has been reproduced at the receiv-ing end.

Double ModulationOf course the 1,000 kc frequency can-

not be heard in the receiver because itcarries nothing. But there is no reasonwhy it should not carry a musical pro-gram or some other intelligence. Itcould have been modulated before it wasimpressed on the 20,000 kc carrier. Andit could have been modulated with thesame equipment that is now used tomodulate a broadcast frequency.

If it had been, the detector in thebroadcast receiver would have convertedit to a current of audible frequency andthe loudspeaker would have convert,. Ithat to sound.

Many Frequencies Ride ThroughJust as many audio frequencies rode

from the studio to the receiver on theback of the radio frequency carrier, somany radio frequencies can ride from theshort wave transmitter to the short wavereceiver on the short wave, or high fre-quency, carrier. Each one of these car-ried radio frequencies in turn cancarry all the audio frequencies, and anyone of them can be picked out of theplate circuit of the short wave detectorby the ordinary radio receiver.

So all that is necessary to provide an-other broadcast band within tuning rangeof the ordinary receiver is to modulatethe broadcast frequencies as is now done,impress all, these modulated radio f e-quencies on a single high frequency car-rier, and then to prefix a short wave re-ceiver to the ordinary broadcast receiver.

A ProblemHow to impress these modulated broad-

cast frequencies on the high frequencycarrier is a problem for , the radio en-gineers to solve. It does not seem in-superable, particularly if the radio fre-quencies are spaced 50 kc apart. Moredifficult problems have been solyed andare being solved as a matter of routinein the large development laboratorieshere and abroad.

The experimentally inclined radio fancan readily test the theory by setting upa small high frequency oscillator in hishome and modulate its output by the

L2

A- Fl+A CIRCUIT DIAGRAM SHOWING HOW TO RECEIVE DOUBLY IN MODU-LATED HIGH FREQUENCY WAVES ON THE ORDINARY BROADCAST

RECEIVER BY PREFIXING A SHORT WAVE TUNER AND DETECTOR.

ANTENNA COIL OF BROADCAST RECEIVER

_J

modulated radio carriers from a fewbroadcast stations. Then he can receivethe high frequency by setting up a suit-able receiver in another part of his home.The transmitting oscillator should not bea power tube for then it might create adisturbance which might bring the wrathof the radio supervisor on him. A -01Atube or even a -99 could well be used.

For receiving the local broadcastingstations a tuner and RF amplifier arerequired for each station, but no detector.The tuners in this case need not neces-sarily involve tuning condensers, for fixedcondensers can be used and each circuitcan be adjusted to one station by varyingthe inductance coil.

Circuits SuggestedThe modulator and transmitting oscil-

lator may take the form shown in Fig. 1.There are three broadcast RF amplifiersA, B and C, each tuned to a separate fre-quency about 50 kc apart, or more. Theseamplifiers may be connected to separateantennas if desired.

All these amplifiers feed into the gridcircuit of the same modulator tube M.Each of these amplifiers then "talks into"the modulator grid circuit, but each talksat a frequency which is the carrier of thebroadcast receiver tuned in.

In the modulator plate circuit is a radiofrequency choke coil RFC. It shouldhave sufficient inductance to look like avery high impedance to the input. fre-quencies. But it should not offer muchimpedance to audio frequencies. Itmight be a Yi henry RF choke coil.

The plate currents for both the oscil-lator and the modulator flow through thischoke, and the plates of the two tubesare connected together, except that ahigh frequency choke HRFC is put inthe plate circuit of the oscillator Osc.This coil serves to prevent the ultra -highfrequency of the oscillator to passthrough the distributed capacity of RFCand of the plate circuit of the modulatortube. Its value would depend on whatfrequency is selected for transmission.For ten million cycles a 150 microhenry

`BROADCAST- RECEIVER

coil should suffice.Those famil ar with circuits will rec-

ognize that this is Heising's method ofmodulation.

Heising ModulatorCondenser Co should be a midget 100

mmfd. or smaller and the grid leak GLmay have a value from 10,000 or 50,000ohms.

The oscillator coil Ll of course de-pends on the freqtiency desired. It may,for example, consist of 3 turns of No. 14bare wire wound to a diameter of 5inches. Whether or not condenser Cl isnecessary depends on the frequency de-sired and on the stray capacities. Thecircuit will probably oscillate at a highfrequency without it, and the actual valueof the frequency for a test set is of noimportance. The frequency will be higherwithout the condenser than with it. Atany rate Cl should only be a midget ifused.

The grid return should be connected tosome point near the middle of the threeturn coil. The lead should terminate ina clip so that the position can be adjustedfor best results.

The oscillating coil Ll will serve forthe radiating antenna.

While the frequency of this oscillatormay not be as high as 20,000 cycles it willbe high enough to serve the test.

The ReceiverThe receiver of this system is much

simpler. The wave collector may be aloop just like Ll with a midget condenseracross it. The two loops should be point-ing in the same direction. Fig. 2 showsa possible hook-up.

The grid leak R1 may be of 5 megohms,the grid condenser C2 of 100 mmfd. orless. Cl is a midget variable condenserand L2 is a coil of the same specifica-tions as Ll in Fig. 1. C3 can also be asmall condenser of 100 mmfd.

The regeneration can be varied by slid-ing the clip at the end of the grid returnon the three turn coil. The receivershould not oscillate.

Inversion of SpeechMatter of Sidebands

Inversion of speech so that the highaudio frequencies come through as lowfrequencies and so that the low comethrough as high is a problem in modula-tion and the selection of the lower sidehand. If the speech frequencies range

from 0 to 10,000 cycles the lower sideband will range from 10,000 to 0, or thelower side band will be the speech bandinverted. It is only necessary to insertappropriate filters in the circuit to selectthe lower side band.


LiteratureWanted

HE names and addresses of readers ofT RADIO WORLD who desire literatureon parts and sets from radio manufactur-ers, jobbers, dealers and mail order housesare published in RADIO WORLD on re-quest of the reader. The blank below maybe used, or a post card or letter will doinstead.

RADIO WORLD,145 West 45th St., N. Y. City.

I desire to receive radio literature.

Name

Address

City or town

State

E. C. Stansfield, 686 E. Sec. St., Highfire, Pa.C. G. Schwille, Tannersville, N. Y.J. H. Walker, 12 Front St., New London, Conn.Carl Alverson, Dansville, N. Y.Joe Nathan, P. 0. Box 242, Beacon, New York.Chas. Van Cleve, 8012 89th Ave., Woodhaven,

N. Y.Livingston Lansing, Box 54, Salisbury, Conn.Al Johnson, 1409 Shelby St., Sandusky, Ohio.Ascorra Huss, P. 0. Box 2334 Lima, Peru '

F. A. Coyen, 1 Morin Ave., ISanielson, Conn.M. P. Fox, 1280 Marcy St., Akron, Ohio.Joseph D. Andrew, Route 3, Box 233, Salisbury,

North Carolina.Alfred Q. Carroll, 3220 17th St. N.W., Washing-

ton, D. C.Lon J. Gray, 4970a Delmar Ave., St. Louis, Mo.0. H. Stephens, 1806 Fairmont Ave., Philadel-

phia, Pa.C. B. McCarttey, 9 Barbara St., Jamaica Plains,

Mass.E. A. Chimner, 2539 Chevrolet Ave., Flint, Mich.

F. W. Suseny, 1600 Jackson St., San Fran-cisco, Calif.

Leonard B. Wormall, 116 Quebec St., Lowell,Mass.

W. A. Spangler, Wyoming, Ohio.Robert S. Lytle, Harlingen, Texas.C. R. Gray, Box 625, Nevada City, Calif.H. Arnold Jackson, Box 625, Nevada City,

Calif.L. S. Ross, 1288 Second Ave., San Francisco,

Calif.Barney Coleman, 1162 N. Sierra Bonita St.,

Pasadena, Calif.G. F. Welsh, Box 21, Pleasant Hill, Mo.

Geo. J. Night, 23 Water Blvd., Auburn, N. Y.Louis Warren, 1318a No. 21st St., St. Louis, Mo.Henry H. Koch, Jr., 48 West 120th St., New

York, N. Y.Harold Schooley, Allenwood, Penna.Stanley M. Craven, 302 Runnymede Ave., Jenk-

entown, Pa.V. E. Crosby, Hinckley, Minn.Louis Ad in, 1335 Boynton Ave., New York, N. Y.Lawson Jones, R2 Box 222, Danville, Ill.James Millen, 28 Wedgemere Road, Malden, Mass.C H. Wagner, 12734 Oak St., Binghamton, N. Y.0. R. Allen, 322 Dundas East, Toronto, Ont.,

CanadaWillice E. Groves, 15th Service Co., Fort Mon-

mouth, N. J.Martin Fahey, 1935 Harlan St., Philadelphia, Pa.Dan McKinnon, 157 Roxbury St., Roxbury, Mass.R. H. Van Dooser, 13 Remoleno St., Buffelo,

N. Y.Owen Cunningham, R. R. A., Kingfisher, Okla.Joseph A. Krulfeifer, 399 Bleecker St., Brooklyn,

N. Y.S. Marini, 102 Intervale St., Quincy, Mass.Joseph Marshall, 525 Devitt Ave., Campbell, Ohio

A. Newell, 146 Harding Place, Syradise, N. Y.A. W. Burgess, 1019 E. 49th St., Cleveland, OhioHarry A. Drew, 424 14th St., West New York,N. J.John Mathews, 765 St. Johns Place, Brooklyn,N. Y.Chas. Yerigan, Box 384 Alexandria, Minn.W. H. Williams, 606 So. 17th Ave., Ilumblodt,

Tenn.G. Wise, 115 Margaret St., Sarnia, Ont.Arthur J. LeMay, 94 Ford St., Lynn, Mass.Myron F. Church, 901 S. Harvard Blvd., Los

Angeles, Calif.David E. Ratcliffe, Box 846, 312 Cutler St.,Raleigh, N. C.Cleo Balanzar, 29-C Guy Place, San Francisco,

Calif.Roy A. Anderson, 703 Puget Ave., Sedro Woolley,

Wash.Forrest M. Beeson, 246 East Ave. 39, Los Angeles,

Calif.Carl P. Sorensen, 3843 N. Ridgeway Ave., Chi-

cago, Ill.John Reardon, 400 West 52nd St., New York CityArthur H. Ellis, 43 East Ave., Middletown, N. Y.Robert B. Riester, 15 Benton St., Stafford Springs,

Conn,

The Radio TradeCoolidge Pr

BakeliteWashington.

The Department of the Treasury hasmade public the text of its circular tocustoms officers carrying out the embargoorder placed by the President against im-portations of laminated insulation pro-ducts sold in the United States as bake-lite, and used extensively for radio panels.

Complaints had been made to the TariffCommission that importers were bringing into this country products which sim-ulate the bakelite material and it wasclaimed these were infringing on theAmerican patents covering the manufac-ture of bakelite.

The President directed, therefore, re-fusal of entry of such products in the caseof any shipment as to which doubt existedas to the infringement, and in carryingout this order, the Treasury advised Col-lectors of Customs to make a full reportof consignments of this character imme-diately upon presentation at the customshouses.

Full Text of AnnouncementFollowing is the full text of the an-

nouncement:"The Department has been advised by

the President that Formica InsulationCompany, Continental Fibre Company,Fibroc Insulation Company, NationalVulcanized Fibre Company, SpauldingFibre Company, Inc., and the BakeliteCorporation, engaged in the manufactureand sale in the United States of lamin-ated products composed of paper or othermaterials and an insoluble and infusiblecondensation product of phenols and for-maldehyde, have made complaint askingrelief under section 316, Title III, of the

ohibitsBootleggingTariff Act of 1922, front unfair methodsof competition and unfair acts in the im-portation or sale of such laminated prod-ucts.

"The President has also advised thatupon the facts submitted to him by thereason to believe that laminated prod-ucts are offered or sought to be offeredfor entry into the United States in viola-tion of said section 316, and that thecontinuance of such anparent violationof section 316 pending completion of finalfindings by the United States Tariff Com-mission, will work substantial injury tothe industry of the complainants.

Refusal Ordered

"The President has, therefore, by au-thority of subdivision (f) of section 316of the Tariff Act, directed that entry beforbidden into the United States oflaminated products in the manufactureof which synthetic phenolic resin varnishcovered by United States letters patentNos. 1018385 and 1037719 was used, pro-vided that the presence in the laminatedproducts of an insoluble and infusiblecondensation product of phenols and for-maldehyde shall be satisfactory evidencethat said synthetic phenolic resin varnishwas used in their manufacture, unless thecontrary shall be established.

"In the event any such merchandise isoffered for entry in your district, which,in your opinion, constitutes an infringe-ment of the President's order, the entrythereof should be refused and in the caseof any shipment as to which any doubt ofsuch infingement exists, you should sub-mit a report thereof to the Department forinstructions, together with a sample."

C. Arthur Liacos, West Groton, Mass.E. B. Polk, Cheriton, Va.Thomas L. Marshall, 196 Woodside Ave., Buf-

falo, N. Y.0. R. Allen, 322 Dundas East, Toronto, Ontario,

CanadaArthur C. Ocasin, 58 E. 106th St., New York

CityChauncey B. McGill, 221 Manhattan Ave., Jersey

City, N. J.F. H. Parks, 1915 Garrard St., Covington, Ky.L. E. Mattler, 9137 A. South Broadway, St.

Louis, Mo.Sidney Nordgren, 42 McGovern Ave., Ashtabula,

OhioArchier Miller, 19 Nashua St., Manchester, N. H.John A. Dutea, 29 Pearl St., Town Hall, Prov-

incetown, Mass.W. A. Ellis, 424 Drakert St., Hammond, Ind.W. M. Blaney, 500 S. Smallwood St., Baltimore,

Md.Anton Dyczus.579 Summer St., W. Lynn, Mass.C. Wilson, 155 N. Mechanic St., Cumberland,

W. C. Thomas, 139 Chestnut. Holyoke, Mass.Wm. Hamsell, 116 E. Main St., Ottumwa, Ia.Wm. L. Morrissey, 337 No. 41st St., Camden,N. J.Vernon V. Vaupel, 2106 Lunt Ave., Chicago,

P. Cohen, 635 E. 21st St., Brooklyn, N. Y.H. B. Robeson, 554 Myers St., Toledo, Ohio.

James G. Parsons, 1821, Duquesne St., McKees-port, Pa.

Holstein Kerr; 5 Castle Ave., Upland, Pa.C. W. Studivant, 1007 West 5th St., Austin,Texas.S. C. Irvin, 2959 California St., Denver, Colo.Chas. Rich, 119 Post Ave., New York, N. Y.Charles L. Banker, 130 South Ave., Pough-

keepsie, N. Y.S. Watkinson, New Lebanon, N. Y.R. W. Phelps, 5127 Centre Ave., Pittsburgh,

Pa.Ernest R. Eybel, 605 Winchester Ave., New

Haven,Conn.Leo H. Ware, 2338 E. 85th St., Cleveland, Ohio.E. C. Taylor, 1738 5th St., S.E., Canton, Ohio.

F. W. Rohrs, Phila. Rd. and Hamilton Ave.,Rosedale, Md.

Stanley Carpenter, 516 Locust St., Kalamazoo,Mich.

W. H. Gemmel!, Homer City, R.D. No.. 2,Penna.

Samuel C. Hyer, 79 Fairview Ave., PortWashington, N. Y.

Bayard E. Bryan, 596 Eshelman St., High -spire, Penna.

L. C. Leach, 444 Fifty-first St., Brooklyn, N.Y.Weightman Radio Shop, 132 N. 5th St., Mid-

dletown, Ind.Hyman Sobel, 2047 73rd St., Brooklyn, N, Y.James Millen, 28 Wedgemere Road, Malden,

Mass.Peter E. Greene, 21 Briggs St., West Warick,

R. I.F. M. Cornwell, Webster, S. D.E. J. Umphrey, 82 Vine St., Dayton, Ohio.H. G. Turner, Box 473, Hopewell, Va.S. R. Bevier, 763 Woodlawn Ave., Jackson,

Mich.P. P. Wells, 756 East 11th St., Pittsburgh, Pa.

A. A. Valentine, 427 W. 154th St., New York,.N. Y.

Frank J. Seib, 64 Lincoln Road, Brooklyn, N.Y.R. Twombley, 1389 N. Sierra Bonita Ave.,

Pasadena. Calif.M & D Radio Co., 1411 East 35th St., Kansas

City, Mo.R. S. Lytle, Harlingen, Texas.James S. M. Neves, 218 W. Main St., Alham-

bra, Calif.Elton Kelley, 3327 College Ave., Kansas City,

Mo.Herman R. Wallin, 693 Watkins St., Brooklyn,.

N. Y.Dr. Earl R. Hoskins, 17 N. State St., Chicago,

Ill.J. Polnik, 9117 W. Lafayette Ave., Detroit, Mich.Lewis G. Dale, 302 East 95th St., New York CityI. Ralph Lloyd, Lloyd In. Studio, 20 West 22nd

St., New York CityHenry Roese, 797 Quincy St., Brooklyn, N, Y.William Mittel, 1310 E. Price St., Philadelphia,.

Pa.Stanley M. Craven, 302 Rannymede Ave., Jenkin-

town, Pa.


Expert Efficiency Dataon the World's Record Super 10

/SHE construction of Scott's WorldsRecord Super 10 .was described in the

March 24th and 31st issues. Trouble -shoot-ing is discussed herewith.

IN SHOOTING trouble in any set it isalways well to use a tube cnecker or

tube tester. This usually consists of twoor three meters in a handy case, withsocket attached, so that a tube may beremoved from the receiver and placed inthe tester's socket, a plug being insertedin .the vacant receiver socket. Two metersusually consist of milliammeter and low -reading voltmeter, to test plate currentand filament voltage. It is well to havea third meter to test B voltages, prefer-ably a 0-500 high resistance voltmeter.

If you have no tube tester, the next bestthing to do is to remove your tubesfrom your set, take them to a friend whohas a set operating using the same typeof tubes, and place them in his receiverone at a time, noting if the receiver func-tions properly as each tube is inserted.

If you find that the receiver does notoperate when one particular tube is in-serted, it shows that the tube is defective.

Have Extra Tubes HandyRemember, just one bad tube will up-

set the operation of your whole receiver.It is a good idea to have one or two newtubes on hand at all times, and if you arein doubt as to the condition of your tubes,take one of the new ones and insert it inturn in each socket. If your signalstrength increases, it shows that the tubeyou have replaced is not working effi-ciently.

We have recently found that the -40tube (high mu) makes the most efficientfirst detector. This is the tube locatedthird from the end. Use a -01A for thesecond detector. Under certain condi-tions, the 112A also makes a good seconddetector, but never use a 10, or a -00Aas a second detector.

If you find that the receiver has atendency to start howling when you turnup your -potentieometer to get any degreeof volume, and especially if this- occurswhen" you have the speaker and set to-gether in a console cabinet, or whenspeaker is near the receiver, you probablyhave a microphonic tube.

Keep Speaker Away from SetIt is always a good idea to keep the

speaker away from set five or six feet.Generally, the tube in the second de-

tector socket is the one that will causethe trouble. To test for this, hold thesecond detector tube firmly with yourhand, noting if the hum or howl stops.If it does, then you know positively thatthe tube is microphonic. Try the othertubes in set in second detector socket,and you will probably find one that isnot microphonic.

How, to Balance CondenserThe results that you obtain particularly

with regard to selectivity, tone qualityand distance, depend on the careful bal-ancing up of the three gang condenser.This gang condenser has three small trim-mers between the plates, and before youcan get proper selectivity and sensitivity,these trimmers must be adjusted so thatthe two RR stages are correctly balanced.

The best way to adjust this condenser is

By E. H. Scottas follows: Tune in a station between300 and 370 meters. Then with a woodenscrewdriver loosen the small screw on thetrimmer next to the drum dial. Now loos-en the screw on the trimmer in the centeruntil it is about half way out. Next seethat the plates on the small midget con-denser on the front panel are half out.You are now ready to start adjusting.

First, retune the station between 300and 370 meters until you have the 'bestvolume. Second, adjust the trimmer atthe end of condenser until you get themer near the drum dial. While adjustingscrew on the center trimmer in or out, un-til you get the loudest signal.

Finally, adjust the screw on the trim-mer near the drum dial. While adjustingthe trimmers, tune station by moving theknob on the gang condenser slightly oneway or the other, noticing that the stationsnaps in and out. Make sure that youdo not get the station at two points onthe dial a few degrees apart; that is, getthe station in a one point on the dial, thenas you turn dial further get a silent spaceand bring in the station again. If this oc-curs, it proves that the gang is not bal-anced- correctly.

Oscillation BeginsYou may notice while adjusting that

the radio frequency tubes will go intooscillation. This will show that you areapproaching the proper point. When thisoccurs, lower the filament voltage a trifleon the two RF tubes. (controlled by therheo stat below voltmeter), and continueadjusting.

If you find that in balancing the firstand center trimmer, it has very little ef-fect on the increase in volume of the sta-tion, it is a sign that there is either ashorted stage or an open stage.

First, check up your wiring on the twoRF tubes, and see that everything iswired according to the blueprints. Makesure that you have inserted the transform-ers correctly. Sometimes constructors getthem reversed or get the 530 or 520 inwrong places.

Next unsolder the connections on yourthree gang condensers; then take thevoltmeter and small C battery, or a pairof headphones and C battery, and testacross the terminals of each individualcondenser. If headphones are used, thereshould be no click heard, and if a volt-meter, there should be no reading. Ifthere is a reading, it is a sign that thatparticular condenser is shorted, and itshould -be returned for adjustment to theRemler Co. The same check should bemade on the small midget condenser onthe front panel.

First unsolder the leads running to it.There should be no click or reading whentesting across the two terminals, norshould there be a click in the phonesor a reading when the plates are ro-tated.

If, after testing the condensers you canfind nothing wrong, remove the B530, andthe two B520s, test from S to F post andfrom P to B post. There should be aclick or reading between each of these.If there is no reading or click betweenthese points, it is a sign of an open trans-former and should be returned to factoryfor replacement.

Next test between the S toP posts, then

between F and B posts. There shouldbe no reading on your voltmeter. If thereis a reading, it shows a shorted transform-er and should be returned to factory forreplacement.

First, note that your voltmeter showsbetween 414 and 5 volts. Generally, youwill find that you get best reception atabout 4% volts. However, after the re-ceiver has been turned on for about fiveminutes, the battery will have settled;then by means of the master rheostat onthe subpanel, readjust voltage so that itreads about /4% volts. Turn on the rheo-stat controlling the RF tubes about three-quarters. Turn potentioneter up abouthalf way. Tune in a station by rotatingboth dials together.

You will note that on stations about400 meters, the dials read very close to-gether. However, on the very low wave-lengths, the oscillator dial will read from30 to 40 points higher than the gang con-denser or wavelength dial. On the higherwavelengths, the oscillator will read alittle lower than the gang condenser dial.

Tips on TuningIt is impossible, at the frequency at

whiCh the transformers for the World'sRecord Super Ten are peaked, to makeboth dials run together using the .00035condenser. However, this does not affectthe operation of the receiver or its ef-ficiency, for it is a simple matter to tunein a station and make a note of the dialreadings. Once the station is logged, youcan go to the numbers shown for the sta-tion and it will come in.

You will find it necessary, to stop tubesfrom oscilating, to keep the rheostat con-trolling the RF tubes turned down moreon the lower wave lengths than on thehigher wavelengths. When you have astation tuned in, you can turn this rheostaton until the receiver begins to squeal,then turn back until the squeal disappears.You will then have your rheostat stagesoperating at maximum efficiency.

Now tune in the station, using bothdials, until you get the maximum volumeand best tone quality, and control the vol-ume by means of the potentionmeter.This will enable you to regulate the vol-ume from a whisper to maximum volume.The midget condenser on the lefthandside of panel is used to bring in distantstations with maximum volume and also tokill off interference.

The best antenna to use with theWorld's Record Super Ten is one about50 feet long, including the lead-in. Youwill find that you will get better resultswith the antenna facing in one particulardirection. In Chicago, on the North Side,stations on both coasts come in best withthe aerial facing East and West, How-ever, if you are near a very powerfulbroadcasting station, a little experimentingwith the direction of your aerial will en-able you to eliminate this station easier.

The best ground to use is a copperplate with your ground wire soldered to itand buried five or six feet in damp earth.The next best ground is a ground clampwith wire or a cold water pipe. The nextbest a ground clamp and wire on a radia-tor or radiator pipe.

A good ground is absolutely necessary ifyou wish to obtain maximum results fromyour receiver.


A THOUGHT FOR THE WEEKTrillE,V, during, recent years, a well -Pr known player disappeared from Broad-way and the speaking stage, in all likelihoodhe could be found in one of the motion pic-ture studios. Now the broadcasting studioalso gives work and shelter to many a playerwho, not so long ago, before our native le-gitimate stage became a thing of rags andtatters, strutted his brief hour before thefootlights and bowed to the plaudits of hisadmirers. Cold silence is his reward now-silence and a more or less plethoric envelope on pay day. 'Tis a merry world, mymasters! Merry-but so still and cold.But-there's the envelope!

SEVENTH YEAR

The First and Only National Radio Weekly

Radio World's Slogan: "A radio set for every home."

TELEPHONES: BRYANT 0558, 0559PUBLISHED EVERY WEDNESDAY

(Dated Saturday of sane week)FROM PUBLICATION OFFICE

HENNESSY RADIO PUBLICATIONS CORPORATION195 WEEP 45TH STREET, NEW YORK, N. Y.

(Just east of Broadway)ROLAND BURKE HENNESSY, President

IL B. liEWNESSY, VicePresdentHERS AN BERNARD, SecretaryChicago: 55 West Jackson Blvd.

Kansas City, Mo.; H. A. Samuelson, 300 Coca Cola Bldg.Los Angeles: Lloyd Channel, 811 S. Coronado St.

European Representatives: The International News Co.Breams Bldgs., Chancery Lane, London, Eng.

Paris, France: Brentxtno'a, 8 Avenue do loped,

EDITOR, Roland Burke HennessyMANAGING EDITOR, Herman Bernard

TECHNICAL EDITOR. 1. E. AndersonART EDITOR. Anthony Sodaro

CONTRIBUTING EDITORS:lames H. Carroll, John Murray Barron and

Capt. Peter V. O'Rourke

SUBSCRIPTION RATESBeen cents a copy.. $6.00 a year. $3.00 for sit

months. $1.50 for three months. Add $1.00 a yearextra for foreign postage Canada, 50 cents.

Receipt by new subscribers of the first copy of RADIOWORLD mailed to them after :lending in their order.is automatic acknowledgment of their subscription order.Changes of address should be received at this office twoweeks before date of publication. Always, give old address;also state whether subscription is new or a renewal

Equal Franchise Wins;Board Life Preserved

Washington.The radio bill, continuing the Commis-

sion for another year and including amodified "equal franchise" provision, wasadopted by the House and the Senate an&sent to President Coolidge.

The President carefully considered thebill and then signed it.

The equal franchise provision directsthat the total power for each of the fivezones be the same, except that whereapplications are lacking in one zone, tem-porary grant of such spare power waybe made to another zone. This exceptionwas a Senate amendment to the originalabsolute House provision. The amend-ment, originally and as adopted, was de-signed to grant greater power principallyto the South.

Provisions of BillSection 5 of the bill deals with equal

franchise as follows :"It is hereby declared that the people

of all the zones established by Section 2of this act are entitled to equality of radiobroadcasting service, both of transmissionand of reception, and in order to providesaid equality the licensing authority shallas nearly as possible make and maintainan equal allocation of broadcasting licens-es, of bands of frequency or wavelengths,of periods of time for operation and ofstation power, to each of said zones whenand in so far as there are applicationstherefor; and shall make a fair and eq-uitable allocation of licenses, wavelengths,time for operation and station power

each of the States, the District ofColumbia, the Territories and possessionsof the United States within each zone,according to population.

"The licensing authority shall carry intoeffect the equality of broadcasting servicehereinbefore directed, whenever necessaryor proper, by granting or refusing licens-es or renewals of licenses, by changingor reassigning wavelengths, by changingperiods of time for operation and by in-creasing or decreasing station power whenapplications are made for licenses or re-newals of licenses.

The Modification"Provided, that if and when there is

a lack of applications from any zone forthe proportionate share of licenses, wave-lengths, time of operation or station'power to which such zone is entitled, thelicensing authority may issue licenses forthe balance, of the proportion not appliedfor from any zone to applicants from

other zones for a temporary period ofninety days each, and shall 'specificallydesignate that said apportionment is onlyfor said temporary period. Allocationsshall be charged to the State, district, ter-ritory or possession where the studio ofthe station is located and not where thetransmitter is located."

Senator McKellar, (Dam.), of Tennes-see, sought to have the measure recom-mitted with a substitute for the redis-tribution clause under which the FederalRadio Commission is directed to make areallocation of stations, wavelengths andpower for each of the five radio zones ofthe country. Senator McKellar said hewanted to correct the ambiguity in theredistribution clause. His motion wasruled out, of order by Vice -PresidentDawes.

Shorter LicensesThe bill, in providing that the terms

of the present members of the FederalRadio Commission shall expire at the endof one more year, also continues theCommission's authority for a year.

Broadcasting station licenses, under thebill, are to be issued for no longer thanthree months, and all other licenses forno more than one 'year.

Senator Dill (Dem.), of Washington,criticized Commissioner 0. H. Caldwell,of New York, for stating that the re-distribution clause of the radio bill wasunworkable.

The Washington Senator declared thatstations affiliated with the Radio Corpora-tion of America had obtained the "lion'sshare" of the station power and hence,the equalization plan was needed.

Victor Deal DiscussedNegotiations under way for a merger

of the Victor Talking Machine Companywith the Radio Corporation were broughtinto the debate on the bill. Senator King(Dem.), Utah, charged the Radio Corpora-tion with being part of a "trust" seekingto control the radio field, asserting thatthe acquisition of the Victor Company wasfor the purpose of assuring the otherbroadcasting stations the use of Victorartists hitherto denied.

Indications are that the new law willcurtain the number of licenses and thepower of such centres as New York andChicago. It is the understanding that un-der one tentative plan the number of sta-tions throughout the country would bereduced from 685 to 550. This again raisesthe Constitutionality question.

Separate B SupplyAdvocated for Audio

ADVERTISING RATES- General Advertising

1 Page, 7%." x 11" 962 lines $300.00% Page, 7%" x 5%" 231 lines 150.00% Page, 8%," D. C. 231 lines 150.00

5.9. Page, 432" D. C. 11$ linee 75.00'A Page, 4%" S. C. 57 lines 37.501 Column, 2%" x 11" 154 lines 100.001 Inch 10.00

Per Agate Line .75Time D !went

52 consecutive issues 20%28 tlmea consecutively or E. 0. W. one year 15%13 times consecutively or E. 0. W 12%%

4 consecutive issues 10%WEEKLY, dated as Saturday, published Wednesday.

Advertising forms close Ttlesday, eleven days in advanceof date of issue.

CLASSIFIED -ADVERTISEMENTSTen rents per word. Minimum 10 words. Cash with

order. Business Opportunities, ten cents per word. $1.00minimum.

Entered as secondclass matter March 23, 1922, atthe Peat Office at New York, N. Y., under the Act ofMarch 3, 1879.

Eveready Reduces Price;Adds New Layerbilt

The National Carbon Company, mak-ers of Eveready radio batteries, an-nounced a new smaller size EvereadyLayerbilt B battery, No. 485, as an itemadditional to its large size Eveready Lay-erbilt B battery, No. 486.

A price reduction on the two leadingEveready round -cell B batteries, the Nos.770 and 772, also was announced.

A device announced by the WholesaleRadio Service Company, 6 Church Street,New York City, is the Ra-pam AudioUnit, for use with practically all makesand models of radio receivers and alsofor phonograph reproduction.

The Ra-pam is a completely self -con- -tained, light -stock operated two -stage am-plifier. A heater -type AC tube is used inthe first -stage and two 210 type powertubes in the second stage. A 281 typerectifier tube is used to sapply the B cur-rent through the power transformer andfilter system, which is self-contained in ametal case approximately 15 x 11 x 7". The

Ra-pam will fit nicely into most consoles.The Ra-pam does not supply the B cur-rent for the tubes in the set that remainin use after the Ra-pam is connected.

The sponsors said:"Six months hence the trade will ac-

knowledge the step taken in the designof the Ra-pam as a great advance overpast practice. The idea of supplying allthe tubes in a radio receiver from thesame B eliminator filter' system is thecause of much trouble that has been ex-perienced in the form of rnotorboatingand audio distortion. A separate' B sup-ply is better."


Clustorn Builders,. AssociationCustom -Built Radio, IncCustom -Built Radio Set GuildCustom Radio Builders AssociationCustom Radio Builders ClubCustom Radio Builders GuildCustom Radio Builders, IncCustom Radio Builders of AmericaCustom Radio Builders Service ClubCustom Radio GuildCustom Set Builders AssociationCustom Set Builders ClubCustom Set Builders Club of AmericaCustom Set Builders GuildCustom Set Builders, IncCustom Set Builders of AmericaCustom Set Builders of U. S. & CanadaCustom Set Builders of the WorldCustom Set GuildCustom Radio Constructors ClubDX Finders ClubGuild of Master RadiotriciansHome Radio Builders Club

HelpName the Baby: Set Builders RushRadi0 r

. .1 Win Raditrician,American Radio Set Builders AssisnationAmerican Radio Set Builders of AmericaAmerican Radio Technicians AssociationAmerican RadiotriciansAmerican Radiotricians AssociationAmerican Radiotricians. IncAmerican Society of Master Set BuildersAmerican Society of Set Builder

.

0

0

00

0Association Custom Radio. Set Constructors 0Association of Radio TechniciansAssociation of Radio Technicians of America. -0

00000000000

00000000000

Institute of Master Radio Receiver Constructors 0Institute of Radio Set Builders 0Institute of RadiotriciansInternational Custom Set Builders GuildMaster Builders of Custom Made Sets

000

Master Custom Radio Receiver Constructors...0Master Custom Radio Receiver Constructors

GuildMaster Radiotricians' Club of AmericaMaster Radiotricians' GuildMaster Radiotricians of America, Inc.Mutual Association of RadiotriciansNacuset Builders' AssociationNaraset Builders' AssociationNational Association Custom RadiotriciansNational Association of Custom Set Builders....0National Association of Radio BuildersNational Association of Radio Set BuildersNational Association of RadiotriciansNational Custom Set Builders ClubNational Custom Set Builders Club of Arnerica..0National Custom Set Builders, Inc 0National Custom Set Builders & Radiotricians

Association 0National Radio Builders' AssociationNational Radio Builders LeagueNational Radio Club

00

0000

000

National Radio Custom Builders Association 0National Radio Set Builders 0National Radio Technicians 0National Radiotricians Association of America -0National Radiotricians CorporationOrganized Institute of Custom Set Builders 0Pioneer Custom Set Builders Club of America -0Pioneer Radio Builders SocietyProfessional Radio Set BuildersProfessional Radio Set Builders of AmericaProfessional Set Builders ClubProfessional Set Builders Club of AmericaProfessional Set Builders UnionRadio Assemblers & Designers InternationalRadio Builders Association 0Radio Builders Club 0Radio Constructors Association 0Radio Craft Club 0Radio Craftsman 0Radio Craftsman Club of America 0Radio Doctors & Set Builders of America 0Radio Engineers Club of America 0Radio Path Finders Club 0Radio Receiver Builders of America 0Radio Repair & Service Club 0Radio Repair & Service Union 0Radio Set Builders Association 0Radio Set Builders Association of America 0Radio Set Builders, Inc.' 0Radio Technical Association of America 0Radio Technical Society of America ClRadio Technique Club of America 0Radiotricians, Inc. 0Set -U -Need Builders 0Society of America Technicians 0Society of Master Custom Radio Set Builders -0Society of Radiotricians 0United Custom Set Builders 0

to Fill QuestionnaireThe custom set builders proved conclusively their real interest in

forming an organization of their own by quickly filling out and sending in

the questionnaire published last week and reprinted herewith. If youhave not filed your answers, please do so now, as the organization willget under way speedily, and it should have every rightful prospect aboard

the band wagon.

Next week the general trend of the answers will be divulged.

Herewith is a questionnaire which all prospective members of the custom setbuilders club should fill out and mail to RAsio Wm.!). 145 West 45th Street, New YorkCity, attention Mr. McCord. If you have already out and sent in one of diecoupons previously published, it is nevertheless necessary to fill out and mail to itAinoWORLD the accompanying questionnaire.

Only from the list of those who send in the questionnaire will those be chosen towhom membership application blanks will be sent.

Please answer all questions frankly. If more room it needed, write on a separatesheet of paper.

Do not hesitate to answer any question. Do not fail to send in questionnaire justbecause you prefer not to answer some question or questions. All replies will betreated in strict confidence. Not even names of those sending in questionnaires willbe published. No obligation attaches to mailing, in a questionnaire. If you want blanksfor others or a duplicate for yourself, write to RAN° Wogtii, enclosing 2c stamp,

Your name

Address

City State

(2) How old are you?(3) Are you a citizen of the United States?(4) If not, of what country?(5)

Do you make custom radio sets as your ex-clusive means of livelihood'

(6) If not, do you make custom radio sets for hireas a side line'

(7) How long have you been making custom radiosets?

(8) How many have you made?(9) If you do not make them for pay, do for

labor?them for others without charge for

labor?(10) Do you make radio sets exclusively for your

own use and enjoyment"(11) From whom do you buy your parts'

(12) Are you an annual mail subscriber for anyradio magazines?

(13) If so, state which(14) If not, do you regularly boy radio magazines

at news-stands?(15) If so, state which

(16) How did you obtain your radio knowledge?

(17) How much did you spend last year (1927)on parts?

(18) Are you a beginner interested in attainingradio knowledge so you may become a customset builder?

(19) Are you neither a custom set builder nor aprospective one, but interested in purchasinga custom made set'

(20) From what institutions of learning were yougraduated? Include public school, high school,college, with addresses

(21) Do you favor incorporation of the prospectivecustom set builders club?

(22) Do you favor co-operative buying by theclub for its members?

i23) pit you favor local brandies of such a club,in addition to the central organization'

IA) What dues, if any, do You think should becharged?

(25) Do you favor the club maintaining a centrallaboratory for the benefit of its members?

(26) And sending out confidential circuits, tubeAnd other data, including blueprints?

(27) What circuits, if any, have you specialized in?

uto How many customers have you?(29) Do you sell factorpmade sets?(30) If no, state which(31) Do you service sets other than those of your

manufacture?(32) Do you accept tune payments for sets you

make?(33) If so, does anybody discount this paper for

yott?(34) What is your gross income per year from

custom set building,(35) Net income from same?'36) Give two references as to your character.

Name of reference

Address

Name of reference

Address(37) Is your set building business in your borne?

or have you a separate place ofbusiness'

(38) Give name and address of two whom yourecommend for membership.

Name

Address

Name

Address

Name

Address(Be sure to choose the name yaw Wald Mclub to bear. See nest column.)


i-Offitigif ANOTHER FENCO HIT!Thousands of Fenco 3 foot Cones have beensold to discriminating radio fans. Again Fencoengineers have produced a triumph.Quantity production-enormous buying power enables usto offer at the lowest price, a high quality complete kit,with full directions for building the famous

FENCO AIRPLANE CLOTH SPEAKERKit consists of wood frame, first qualityAirplane Cloth, Genuine Fenco Master COUn:t, 10 feet phone cord, U. S. specifica-tion Airplane dope and unit support,nails. Nothing else to buy

$2.00 Deposit on C.O D.Absolutely Guaranteed. Dealers Write

FENCO CONE CO.57 MURRAY STREET NEW YORK CITY

VICTOREENSuper CoilsSend for Folder

Geo. W. Walker Co.2525 Chester Avenue

Dept. B Cleveland, 0.

BLUEPRINTSfor

Diamond of the AirUsing Standard Tubes(not shield grid tubes)

4 -Tube Model 25c5 -Tube Model 25c

Send stamps, coin, M. 0. or check.

RADIO WORLD145 West 45th St. N. Y. City

Subscribers: Look at theExpiration Date on

Your WrapperWe -do not like to take your name from

our subscription list without specific in-struction to do so because many of ourreaders wish to keep a complete file of thepaper.

Please, therefore, look at the subscrip-tion date stamped on your last wrapper,and if that date is earlier than the issuecontained in the wrapper, please sendcheck to cover your renewal.

In this way you will get your copieswithout interruption.

Subscription Dept., RADIO WORLD,145 West 45th Street, New York City.

RECENT ISSUES of Radio World, lSc each.Be sure to give date of issue when writing. RadioWorld, 145 West 45th Street, New York City.

Take Your Choice of 7Other PublicationsFor NEW RADIO WORLD Subscribers Ordering NOWRadio World has made arrangements-To offer a year's subscription for any one of the following publications with one year'ssubscription for RADIO WORLD-RADIO NEWS or POULAR RADIO or SCIENCE AND INVENTION or BOYS' LIFEor RADIO DEALER or RADIO (San Francisco) or RADIO AGE.

This is the way to get two publications-for the price of one,-Send $1.00 today for RADIO WORLD-for one year (regular price-for 52 numbers)-and select any one of the other-nine publications for twelve months.

-Add 51.00 a year extra :or-Canadian or Foreign Postage-Present RADIO WORLD subscribers-can take advantage of this offer by-extending subscriptions one year-If they send renewals NOW(

Radio World's Special Two -for -Price -of -One Subscription BlankRADIO WORLD, 145 West 45th Street, New York City.Enclosed find 56.00 for which send me RADIO WORLD for twelve months (52 numbers).beginning . and also without additional cost, Popular Radio, orRadio News, or Science and Invention, or Radio Dealer, or Radio (San Francisco), orRadio Age, or Boys' Life (or $10.00 for a two-year subscription to one address). No otherpremium with this offer.

Indicate if renewal.

Offer Good Until

May 15, 1928

Name

Street Address

City and State

Radio UniversityWHEN I TUNE in WOR on my re-

ceiver I hear a steady flute -like squealnot unlike that produced by the steamwhistle on a peanut stand. I have triedeverything to eliminate it but have notsucceeded. Sometimes it disappears ofitself. Can you explain what causes itand how it can be remedied?

JOSEPH J. CALLAHAN,Brooklyn, N. Y.

The cause of the whistle you hear isanother station which is operating on thesecond harmonic of the frequency ofWOR. The carrier frequency from thatstation modulates with the second har-monic of WOR. This second harmonicis generated in your own set. There isno complete cure for the condition exceptto stop one of the stations. But it canbe reduced by carefully excluding thesignal from the interfering station by tun-ing and shielding.

The interference is caused by one orthe stations which operate on 1420 kilo-cycles. WCDA and WRST operate onthis frequency.

* * *

I AM TROUBLED a great deal by het-erodyning when I tune in distant stations.It seems like I cannot get any distant sta-tions, either west or east, without inter-ference. Is there any way of tuning outone of the stations when the other is de-sired when the two are operating on thesame frequency?

FRANCIS STOESSEL,Milwaukee, Wis.

(1)-Yes, there is one way. If you ar-range the receiver so that it operates ona loop and an antenna at the same timeand adjust the pick-up of the two so thatthey are equal you can entirely elimi-nate one of the stations provided that theyare not in a straight line and on the sameside of you. This is the same methodused in direction finding at sea for elim-inating the 180 degree uncertainty.

SCOTT WORLD'S RECORDBuild the 9,400 -mile receiver. SUPER 10Listen in on all the world.

Easy and economical to construct. Results guaran-teed. Write today for free circuit diagram, parts listand copies of long distance reception verifications.

SCOTT TRANSFORMER CO.7626 Eastlake Term Dept. E Chicago

FOUR, WORLD'S RECORDS* SCOTT'S SUPER TEN *

Official Service Station

lor'r° NEW Vel DIAMOND this AIRSets Built of Tested, Guaranteed Parts. Shipped

Anywhere. Satisfaction Absolutely Guaranteed.

H. & F. RADIO LABORATORIES, Inc.168 Washington Street New York City

BIG REWARBig TIP1121il await you Is BMW If

You wont to mope inure money quickly. 2,111lione be-ing made by others. Get your share NOW. Get com-Plete facts. Send for FREE complete booklet andguide of money -making opportunitlea. Be Sent to got

tide. BARAWIK CO., Dept. 884. Chicago, U. S. A.

BLUEPRINTand Instruction Sheet

for the Silver -MarshallShielded Grid Six

The New ReceiverUtilizing the New lerShielded GridTubes with Their 25 Cents

Powerful Kick.Guaranty Radio Goods Co.

145 WEST 45TH STREETNEW YORK CITY

RADIO WORLD 21

i',

April 7, 1928

Radio's Biggest SeasonForecast by Polymet

Due to enormous business, the PolymetMfg. Corp., manufacturers of filter andblock condensers, bakelite moulded con-densers, wire -wound resistances, etc., hasbeen compelled to take over another floorat 599 Broadway, New York- City.

This additional space will enable Poly -met to increase manufacturing facilitiesand maintain service to the increasingnumber of radio receiver and power unitmanufacturers who are adopting Polymetessentials as standard equipment.

This was the first public announcementmade by Otto Paschkes, president, andNat. C. Greene, vice-president, upon theirreturn from abroad, where they surveyedradio conditions in England and on thecontinent.

The company issued a statement saying:"This optimistic announcement by one

of radio's leading parts manufacturers ishighly significant in the face of rumorsof unsatisfactory conditions at the pres-ent time.

"It is no doubt true that many smallmanufacturers are plowing a hard row andwill be unable to survive, but the an-nouncement of expansion by the PolymetMfg. Corp. proves that the industry isdaily becoming more stabilized and thatthere is an ever-increasing demand forthe products of dependable and financiallystrong manufacturers."

In commenting on the Polymet expan-sion program Mr. Greene said :

"Our growth has not been of the mush-room variety. Polymet is one of the pio-neers in radio, but its growth has beensteady and sure and built on that firmestof all foundations, the determination toproduce and sell quality and service.'

"The orders we now have on hand fromthese manufacturers convinces us that theradio business has only begun to growand that next season will be one of thebiggest in the history of the industry."

Accurate Panel CompilationFor those fans who wish to know which

standard circuit panels may be procuredfrom stock, all drilled and engraved andready for use, Cortlandt Panel Engrav-ing Co., 165 Greenwich Street, New YorkCity, has carefully compiled a list con-taining this information. Every popularcircuit is covered and exact dimensionsare given.

It also contains a price list on all size

THE VERY UNIT FOR EXPONENTIAL HORNSThis purchase directfrom the manufac-turers permits us tooffer this well knownexcellent unit at thespecial price of$3.00. Satisfactionguaranteed. Moneyrefunded If requestedafter a 5-dey trial.Take advantage ofthis offer, and Inyour $3.00 and re-ceive

vast°}0Y

TS Vt,3 (in

littrlemoney.

Berkman Unit, gait Lake City, Utah Suitable for the Ex -poem° magnet Moving Armature ponentlal or the usual

List Price, $0.00 cabinet horn.Tested and Approved by Radio World Laboratories

N. Y. C. RADIO SALES CO.2230 OCEAN AVENUE, BROOKLYN, N. Y.

THE A C KARAS EQUAMATIC-Full descrip-tion, analytical article, in Feb. 11th and 18thissues. Send 30c for these isues and get freeblueprint. Radio World, 145 _West 45th St., N. Y.City.

EVERY FRIDAY at 5.40 P. M. (Eastern Stand-ard Time) Herman Bernard, managing editor ofRadio World, broadcasts from WGI3S, the GimbelBros. station M New York, discussing radio topics.

POWERand

QUALITY

With the introduction of thenew UX250 and CX350 tubes,Silver -Marshall are ready withthe new 681-250 and 682-250Power Amplifiers. The 681-250is a one stage power amplifierand may be added to any exist-ing first stage audio system.The 682-250 is a complete ACoperated two stage amplifierand may be connected directlyto the detector output. Eithermodel may be had completelywired or in kit form, ready toassemble. Model 681-250 kit,$78.25; Model 682-250 kit,$93.25. Wired models are $15.00additional.SILVER -MARSHALL, Inc.878 W. Jackson Blvd. Chicago, Ill.

plain panels of bakelite and hard rubber.A list of this kind is invaluable to fans andcustom set builders and should be in thehands of everyone. It is also unique,insofar as we know, being the only oneof its kind. It may be had for the ask-ing by addressing the above concern andmentioning RADIO WORLD. --J. H. C.

SM

POWERFUL UNITDrives Any Cone Speakerand Produces Delightful Tone

at Great Volume

Try It for Five Days!If not delighted with it, return itand your money will be refunded.

A Superb CreationAt a Price That $3Fits All Purses .75GUARANTY RADIORADIO GOODS CO..

145 West 45th St., Now York City.Please send lee one cone speaker unit ae adrer.

Used. I will pay postman 43.75, plus few seatsextra ter postage. Your 5 -day money -back guarantyIs accepted.

Name

Address

City State

RheostatsFixed Condensers

JacksUsed in the majority of popular cir-cuits. Experienced designers realizenothing can successfully be used inplace of Carter parts.

l'Carter Radio ColCN ICAGO

RECENT ISSUES of Radio World, 15c each.Be sure to give date of issue when writing. RadioWorld, 145 West 45th Street, New York City.

BRETWOODVariable Grid Leak

De Luxe Model

-e,i41111111111111NE

BETTER BY FAR, than any fixedleak in the detector circuit is theBretwood Variable Grid Leak.

DON'T SEND A SOLITARY CENTThe Bretwood Leak may be baseboard or panelmounted. Works the same in any position. Nofluid used.- - - - - - - - - - - - - - -Guaranty Radio Goods. Co.,145 West 45th Street,. N. Y. City

Please mail me at once one New and Improved1928 Model De Luxe Bretwood Variable Grid Leakwith one Bretwood Bullet Condenser attached, forwhich I will pay the postman $2.25 on receipt. Bothmust be the genuine Bretwood articles, importedfrom England.

Name

Street Address

City State


FORTY TIMESas Much Amplification!

The New Shielded Grid

4 -TUBEDIAMOND

OF THE AIRDesigned by H. B. HERMAN

and described by him in the February 4

11 and 18 issues of RADIO WORLD.The favorite four -tube design, simple as

can be, takes a great step forward, sothat home constructors of radio receivers,and custom set builders, can build a dis-tance -getting and voluminous set, the partefor which list remarkably low.

The new shielded grid tube is used asthe radio frequency amplifier. That iswhy the amplification is boosted fortytimes over and above what it would beif an -01A tube were used instead.

Such simplicity of construction marksthe receiver that it can be completelywired, skillfully and painstakingly, in twoand a half hours.

All you have to do is to follow the of-ficial blueprint, and lot a new world ofradio achievement is before youl Distantstations that four -tube sets otherwise misscome in, and come in strong. No tuningdifficulty is occasioned by the introductionof this new, extra powerful, startling tube,but, in fact, the tuning is simplified, be-cause the signal strength is so muchgreater.

When you work from the official wiringdiagram you find everything so delight.fully simple that you marvel at the speedat which you get the entire receiver mas-terfully finished. And then when you tunein-more marvels! 'Way, 'way up, somewhere around the clouds, instead of onlyroof high, will you find the amplification!

You'll be overjoyed. But you shouldplace every part in exactly the rightposition. Stick to the constants given, andabove all, wire according to the blueprint!

Front Panel, Subpanel andWiring Clearly Shown

When you work from this blueprint youfind that every part is shown in correctposition and every wire is shown goingto its correct destination by the ACTUALROUTE taken in the practical wiring it-self. Mr. Herman's personal set was usedas the model. This is a matter-of-factblueprint, with solid black lines showingwiring that is above the subpanel, anddotted IMes that show how some of thewiring is done underneath.

Everything is actual sire.Not only is the actual size of the panel

holes and instruments given, but the dimen-sions are given numerically. Besides, itis one of those delightful blueprints thatnovice and professional admire ad much-one of those oh -so -clear and can't -go -wrongblueprints.

Be one of the first to send for this newblueprint, by all means, and build yourselfthis outstanding four -tube receiver, withits easy control, fine volume, tone quality,selectivity and utter economy. It givesmore than you ever expected you couldget on four tubes-and the parts are wellwithin the range of anybody's purse.

The circuit consists. of a stage of tunedRF shielded grid tube amplification, aregenerative detector, and two transformercoupled audio stages.

What a receiver!

$1.00 for 27" x 27" Blueprint,

Send your order today!

RADIO WORLD,145 West 45th St., N. Y. City.Enclosed please and:0 81.00. for which send me at ones one of-

ficial blueprint of the Four -Tube Shielded GridDiamond of the Air, as designed by H. R. Her-man, and described by him in the February 4,11 and 18 issues ef Hullo World.45 cent. soles for Feb. 4th. 11th. 18th Lamm

NAME

ADDRESS

CITT STATE

rlheyi.eBuilt to Last/Don't throw away "Nyour CeCo Tubesbecause you've had themfor a long time. TheyLAST for a long time ---they're built that way.You get your full money's worthof service in: every CeCo Tubeand there's a type for everyradio need.Ask your dealer

to help you choosethe right typesfor your set.

C. E. Mfg. Co., 'me.Providence. R.I.,. U.S.A.

Allow us to introduce to you the --

POWERCLAROSTAT

Tito big brother of the Clarostat family, intendedfor the heaviest jobs 1n radio layouts. In placeof cumbersome and costly wire -wound resistors.Provides exact resistance value required for bestresults, rather than a crude approximation. Avail-able in three ranges -0-10 ohms for filament andlute -voltage control; 25-500 ohms for line -voltagecontrol and certain voltage control; 200-100,000ohms for voltage control In poorer units and elec-trified receivers. Resistance range covered in sev-eral turns of knob providing micrometric resistance.Noiseless operation. Slays put. Rated at 10 wattsfor handling real work. Sold for $5.50.See the Power Clarostat at your dealer,as well as the other types of Clarostat.But be sure you are offered genuineClarostats, in familiar green box andwith name stamped on metal shell. Andask the dealer for literature, or writeus direct.

American Mechanical Laboratories, Inc.285 North Sixth St.

Brooklyn, N. Y.

Acme Wire CompanyAnnounces New Line

The Acme Wire Company of New Hav-en, Connecticut, makers of the well-known Celatsite Wire and Parvolt Con-densers, announces a complete line ofwound by-pass and filter condensers tomeet every requirement of modern radiopractice, including complete groupings ofFilter condensers in handsome metalhousings with lead -in -terminals designedfor the more important AC and DC powersupply units such as Samson,,Thordarson,Hi -Q, Victoreen, Silver -Marshall andAmertran.

V. M. Tyler, president of the AcmeWire Company, says that this companyhas been studying the developments inelectrified radio for several years and hasspent a great deal of money in designingthe special complete groups of housed -amplification service.

Acme Parvolt by-pass condensers arenow available in all standard capacitiesand voltage ratings, while the ParvoltFilter types are made in standard capaci-ties and in ratings of 200, 400, 600 and800, 1000 and 1500 volts. All are testedfor sustained duty and not only meet thestandards of the R. M. A. but have anadded factor of safety self-imposed byAcme to overcome any possibility ofbreakown from the sudden voltagesurgest expected in electrified radio.

SCREEN GRIDDIAMOND

and otherFeatured Circuits

Use only the

HAMMARLUNDPARTS

Specified by the Author

301 Bettart. Atad3as,

ammarlundoRLC/SION

PRODUCTS

FILL OUT AND MAIL NOWSUBSCRIPTION BLANK

RADIO WORLDRADIO WORLD 145 West 45th Street, New York City

(Just East of Broadway)

Please send me RADIO WORLD for months, for which

please find enclosed

SUBSCRIPTION RATES:Single Copy $ .15Three Months 1.50Six Months 3.00One Year, 52 Issues 6.00

Add $1.00 a Year for ForeignPostage; 50c for Canadian Post-age.

Aprn 7, 192S RADIO WORLD

Hammer Moves IntoLarge, New Quarters

The growth of the Hainmer RadioCo., formerly at 303 Atkins Avenue,Brooklyn, necessitated enlarged quartersand they are now located at 142 LibertyStreet, New York City. A complete stockof standard parts in stack at all times,and all the popular kits are carried. Theyare distributors for Magnaformers, ScottSelectone Transformers for the ScottSuper, Silver -Marshall and Sampson Pow-er Blocks. Sets built from these well-known parts are on demonstration. Un-der the able leadership of S. Hammer,this house is prepared to render an evenbetter and greater service to all branchesof the trade. An enlarged mail orderdivision is prepared to make prompt de-livery on all orders.-J. H. C.

Super OscillatorI WISH TO WIND an oscillator coil

for a Super -Heterodyne to tune with a.0005 mfd. condenser. I have a Bakeliteform 2% inch in diameter. What sizeof wire should I use and how many turnson each winding? I want to connect thecondenser across only one winding.

RASMUS SORENSEN,Duluth, Minn.

(1)-Use No. 28 DSC \vire and wind 53turns for the secondary, 40 for the ticklerand 15 for the pick-up coil.

SMOOTHERPOWER!

For "The Diamond of theAir" and other A.C. Sets.Aerovox Non -Inductive Con-densers last longer and filterbetter.

E [Om"BUILT BETTER"

70 Washington St., B'klyn, N. Y.

\LYNCHResistors for very equirement of tilefan builder and en Inner.

ARTHUR H. LYNCH, Inc.1775 Broadway N. Y. C

-} -Includes TheseFamous Karas

Parts:Karns Micrometric Dials,

Karas .00025 Mfd. VariableCondenser, Ortbometric

Karas .00014 Mfd. VariableCondenser, Orthornetric

Karas Subpanel BracketsKaras Harmonik Trans-

formers-and all other parts by

famous manufacturers!Cost of Complete Kit:

-$58-95r

ItReachedHalf Way'Roundthe World !

Os

THE KARAS 3 -TUBESHORT WAVE KIT

1 -.1,t wane kit using the r.nre.n. hart, IP:11

ycnir guarantee of sa! act ! I h, \li, rp,metric. dial, are the ,mlc rd, M !

%%ANC receit It, es tit I tuMut 4

back lash-made of ktkelitt ! Imtantl,quires uu t.lri thug ; screw :rough tuning and vernier. Kara,Variable Ouldensers, built f the Inn 4tinder precision standard..;remer -4 pa' '

broader tuning range! !Mild till, 111.W

complete kit at ),nor deal ,.r write 4.

KARAS ELECTRIC COMPANY4039DA North Rockwell Street CHICAGO

You Need

"VacShileld"for the New 222Shield Grid Tubeto Stabilize Your

SetTHE invention of

these non-magneticshields for Type 201-Aor the new Type 222Tubes prevents inter-sta g e coupling andelectro-static effects,overcoming stray ca-pacities that maketuning of distant sta-tions so difficult.Just the thing to sta-bilize short-wave set,too.Attached in a minute.Order today by mail,

C. 0. D., 51.00

ORANGE RESEARCH LABORATORIES

247-249 McKinley AvenueEast Orange, N. J.

here it is at last! A real 30.inch power cone for only $6.50.The new Excelocone is unlikeother impractical knocked -downcones on the market. Easy tobuild.. Everything furnished andrut to exact dimensions. Simpleillustrated instructions furnishedimpossible to go wrong. Beauti-

ful clear and natural tome. Gets all the notes fromhighest piccolo note (frequency 4,096 per second) tothe lowest bass tuba note (frequency 36 per sec-ond) without squeal, rattle, rumble or distortion.Cone handsomely lithographed in old rose and blackharmonizing colors; base in beautiful brown fros-tene lacquer. Has sold in stores for $32.50 assem-bled. Build it yourself. and sell it to your friends,

Thousands of Whined neon. Send no money.Shipped C.O.D., plus trams company charge.

Indicate size and model desired.

30" Cone, Pedestal Type $7750130" Cone, Wall Type 6.5022" Cone, Pedestal Type 7.2522" Cone, Wall Type 600

MONMOUTH PRODUCTS COMPANY867 E. 72nd St. Cleveland, Ohio

Quick Action Classified AdsRadio World's Speedy Medium for Enterprise and Sales

10 cents a word - 10 words minimum - Cash with OrderSETS BUILT TO ORDER, modernized, re-

paired. Save money on kits and radio supplies.Write. Geibel, 1243 North 30th Street, Phila-delphia. Pa.

FOR SALEMadison -Moore "One Spot" 8 tube Superhetero-dyne in I eautiful Fritz walnut cabinet. Fiat loop.Matched Cunningham tubes. Guaranteed perfect.5115.00. G. Sherwood, 225 Delaware St., Saginair,Mich.

GUARANTEED Safety Razor, with strop, m neat,strong carrying case, 25 cents. First-class, new.Send coin, M. 0. or stamps.-P. Cohen, 236 VaretStreet. Brooklyn, N. Y.

NEW SHIELDED GRID TUBES for Dia-mond, S -M Six or Laboratory Super, Tyrman 70.Price $5 each. Philip Cohen, 236 Varet St.,Brooklyn, N. Y.

MAGNAVOX M7 cone speaker, List $15, Alcondition, used two weeks. Fine tone. Price, in-cluding baffle, $9. Send M. 0. on 5 -day moneyback guarantee. I. Andersen, 118 Goodrich St.,Astoria, N. Y. City.

BE THE LICENSED RADIO DOCTOR in yourcommunity. 57-$10 spare time evenings. Our co-operative plan secures all the work you want.Secure franchised territory now. Write for book-let. Co-operative Radio Doctors, Dept W, 131Essex St., Salem, Mass.

RADIO -BARGAIN BULLETIN. Sets and acces-sories less than wholesale. Unusual offering ofstandard new sets with factory guarantee. Getlisting and save at least half. Columbia Sales,Box 362, Winona, Minn.

RADIO SETS built to order. Sets repaired.Superhets a specialty. Sweeney Radio Shop,Dept. RW, Pearsall, Texas.

LARGE MANUFACTURER of popular pricedRadio Cabinets wants representatives selling radiodealers. Models listing at $13 and up. Well madein large modern plant. Quantity sellers. Straightcommission basis. For full details, address DrawerRW 10, Boonville. N. Y.

AIRPLANE SPEAKER OFFER-One pieceairplaine cloth 24x18, one piece 10x10, one can dopeand apex, all sent for 52.25 postpaid. JeffersonMail Service, Box 184, Maplewood, N. J.

"RADIO THEORY AND OPERATING," byMary Texanna Loomis, member Institute cdRadio Engineers, Lecturer on radio, Loomis RadioCollege. Thorough text and reference book; 886pages, 700 illustrations. Price $3.50, postage paid.Used by Radio Schools, Technical Colleges, 'Uni-versities, Dept. of Commerce, Gov't Schools andEngineers. At bookdealers, or sent on receipt:died( or money order. Loomis Publishing Com-pany. Dept. RW. 405 9th St., Washinaton, D. C.

GUARANTEED Safety Razor, with strop, in neat,strong carrying case, 25 cents. First-class, new.Send coin, M. 0. or stamps.-P. Cohen, 236 VaretStreet, Brooklyn, N. Y.

"RADIOPHONE RECEIVING" by nine special-ists, 75c postpaid. HAIldorson copper -shieldedtransformers 3% to I ratio, $1.25 postpaid. Wm.Wagner, 819 DeKalb Ave., Brooklyn, N. Y. C,


SEND NO MONEY "11111

"Double R" Meters Improve Your SetUse Them to Maintain Accurate Voltages and CurrentsSo That Maximum Reception Efficiency is Assured

Pin Jack 0-6 Voltmeter forA Battery Measurement

This 0-6 voltmeter, No. 306, is especiallyuseful for the No. 25 and No. 28 Radiolas,because it is equipped with pin jacks whichfit into the plugs with which those sets areprovided. The meters may be used in anyhome -constructed set, too, where the builderdesires to place tip jacks on the front panel,so the meter can be plugged in for obtain-

bng reading. The meter maye kept permanently in cir- .50cuit, if desired.

No. 306, 0-6 volts DC

MULTI -TUBE SETMILLIAMMETER

Panel model. Rec-ommended for setshaving six tubes ormore, particularly ifa -71, -10 or -50 tubeis used as the output.May be kept perma-nently in circuit. For

DC measurements 0.100 milliamperes.

No. 390 $1.65POCKET AMMETER

No. 1 For testing dry cells, 0-40ampere DC scale pocket meter.$1.50

POCKET AND PORTABLEVOLTMETERS

No. 8 For testing A batteries,dry or storage, 0-8 volts DCscale $1.65

No. 10 For testing A batteries,dry or storage, 0-10 volts DCscale 1.65

No. 1.3 For testing A batteries,dry or storage, 0-16 volts DCscale 1.65

No. 50 For testing B batteries,dry or storage, but not for Beliminators, 0-50 volts DCscale 1.65

No. 39 For testing B batteries,dry or storage, but not for Beliminators, 0.100 volts DCscale 1.85

No. 40 For testing A and Bbatteries, dry or storage, butnot for B eliminators; doublereading, 0.8 volts and 0.100volts DC scale 2.25

No. 42 For testing B batteries,dry or storage, but not for Beliminators; 0.150 volts DCscale 2.00

No. 348 For testing AC currentsupply line, portable, 0-150volts 4.50

VOLTAMMETERSNo. 18 For testing amperage of

dry cell A batteries and volt-age of dry or storage A batteries, double reading, 0.8volts, end 0-40 amperes DC $1.85

No. 35 For testing amperage ofdry cell A batteries and voltage of B batteries (not Beliminators); double reading,0-50 volts, 0-40 amperes DC 2.00

Also Track Down Trouble in a Jiffyand Permanently Cure It with the

Aid of These Fine Meters

It is absolutely necessary to use a highresistance voltmeter in measuring the volt-age of B eliminators, either across the totaloutput or at any intermediate voltage. A lowresistance meter at least partly short-circuitsthe eliminator and causes the voltage readingto be away off. Sometimes the reading is aslittle as 25 per cent of the total actual voltage.

All "Double R" meters are accurate to 272'per cent, plus or minus, and all, except theammeters Nos. 1 and 338, may be kept per-manently in circuit.

Panel meters take 2 5/64 -inch hole.

Our Complete Meter Catalogueis contained in this advertisement.

TROUBLE -SHOOTING TEST SET

High Resistance Metersfor B

Eliminators

Here is the me-ter you've beenwishing fort A0-300 DC voltme-ter with a veryhigh resistance.Specially madethat way so it will test the output voltages,from maximum to any intermediate voltage,of any B eliminator or grid biasing resistor.It also makes all the measurements of anyother meter of its voltage range, hence willgive correct readings of B batteries, C bat-teries, cells, or any other DC voltage sourcenot exceeding 300 volts. Full nickel finish.Portable type (fits in sack coat pocket eas-ily). Accurate to 2$ per cent, plus orminus. Fully guaranteed. Requires 35 dif-ferent dyes to make. Furnished with longconnecting cords and conven-ient tips. May be kept per- $ .50manently in Circuit.No. 346 -

[Note: 0-500 volts, instead of 0-300 volts,is No. 347. Tests ALL power packs -Price 55.50.]

PANEL VOLTMETERFOR A BATTERIES

The best inexpensive combination for troubleshoot-ing is a "Double R" Tube Checker, comprising a 0-10milliammeter, a 0-6 voltmeter, a switch, a rheostatand a socket. Add a high resistance voltmeter (0-300or 0-500 v.). With these it is advisable to use aplug, so that all you need do is remove a tube froma receiver that you're testing, put the plug in theempty socket and the removed tube in the socket of

the tester. You can immediately find any openor short circuits, broken or flimsy connections,

reversed connections, etc.The "Double R" Cord and Piug, andthe "Double It" Tube Checker are

shown with high resistancemeter.

SERVICE MEN!No. 210 Tube Checker, consists of 0-6 volts DC Voltmeter, 0-10 DC MIIII-

ammeter, Grid Bias Switch, Rheostat, socket. Binding Posts (with in-struction sheet) 96.90No. 21, cord and plug. For connectial meters la A and B leads of areceiver without any dioconnoollons. Terminals correspond with postson No. 210 tube shocker 61.85No. 346 DC Voltmeter (high resistance) 34.50No. 947 DC Voltmeter (high resistance) 95.50The cord terminals of the plug lead. eonespond with the binding hosts of the

tube checker.Now connect the 0-000 or 0-500 volts high reetetance voltmeter tram Ac- to

B+ poets and YOU get all necessary readings. You can test plate voltage fromB eliminators, or any other B supply, DC plate currant and DC filament voltage,as well as the efficacy of the tube, by throwing the grid bias switch. for theplate current should change within given limits, depending on the type of tuba.

ignitly roar testing outfit with the indispaneable combination that constitutesthe Trouble Shooting Teat Set and Tlme-Saver. You quickly locate trouble whileothers Bounder about.Complete Combination 21 (with;. S:10: g::101)..:111:00gComplete Coinbination

PANEL VOLTMETERSNo. 335 For reading DC volt.

ages, 0.8 volts $1.65No. 310 For reading DC volt-

ages, 11-10 volts 1.65No. 316 For reading DC volt-

ages, 0-16 volts. 1.65No. 337 For reading DC volt-

ages, 0-50 volts 1.65 , NameNo. 339 For reading DC volt- I

ages, 0-1003 volts 1.75 r

INo. 342 For reading DC volt-ages, 0-150 volts 1.75 I

No. 340 For reading DC volt- ' City State RW-28ages, double reading, 0-8volts, 0-100 volts 2.25 I

One of the mostpopular meters, the0-6 panel voltmeter,DC. May be keptpermanently in cir-cuit. Panel model.

No. 326

PANEL AC VOLTMETERSNo. 351 For reading 0-15 volts

AC $2.25No. 352 For reading 0-10 volts

AC 2.25No. 353 For reading 0-6 volts

AC 2.25(See No. 348 under "Pocket and

Portable Voltmeters.")PANEL MILLIAMMETERS

No. 311 For reading 0.10 milli-amperes DC $1.95

No. 325 For reading 0-25 milli-amperes pc 1.85

No. 350 For reading 0-50 milli-amperes DC 1.65



DC PIN JACK VOLTMETERSNo.308 For No. 20 Radiola, 0 6

volts DC $2.50No. 307 Desk type voltmeter

with cord, 0-6 volts DC 2.50

6 -VOLT A BATTERYCHARGE TESTER

No. 23 'For showing when 6 -volt A battery needs chargingand when to stop chargmg;shows condition of battery atall times $1.85

PANEL AMMETERNo.338 For reading amperage,

0-10 amperes DC $1.65

I GUARANTY RADIO GOODS CO., 145 W. 45th St., N. Y. City7Please send at once your meters, catalogue numbers:

for which I will pay postman advertised price plus few cents postage.

Address

ALL METERS SOLD ON FIVE-DAY MONEY -BACK GUARANTY.


Plir SEND NO MONEY "ft"Double R" Meters Improve Your Set

Use Them to Maintain Accurate Voltages and CurrentsSo That Maximum Reception Efficiency is Assured

Pin Jack 0-6 Voltmeter forA Battery Measurement

This 0-6 voltmeter, No. 306, is especiallyuseful for the No. 25 and No. 28 Radiolas,because it is equipped with pin jacks whichfit into the plugs with which those sets areprovided. The meters may be used in anyhome -constructed set, too, where the builderdesires to place tip jacks on the front panel,so the meter can be plugged in for obtain-ing reading. The meter maybe kept permanently in air- .50coif, if desired.No. 306, 0-6 volts DC

MULTI -TUBE SETMILLIAMMETER

Panel model. Rec-ommended for setshaving six tubes ormore, particularly ifa -71, -10 or -50 tubeis used as the output.May be kept perma-nently in circuit. For

DC measurements 0-100 milliamperes.

No. 390 $1.65POCKET AMMETER

No. 1 For testing dry cells, 0-40ampere DC scale pocket meter.$1.50

POCKET AND PORTABLEVOLTMETERS

No. 8 For testing A batteries,dry or storage, 0-8 volts DCscale $1.65





No. 40 For testing A and Bbatteries, dry or storage, butnot for B eliminators; doublereading, 0-8 volts and 0-100volts DC scale 2.25

No. 42 For testing B batteries,dry or storage, but not for Beliminators; 0-150 volts DCscale 2.00

No. 348 For testing AC currentsupply line, portable, 0.150volts 4.50

VOLTAMMETERSNo. 18 For testing amperage of

dry cell A batteries and volt-age of dry or storage A bat-teries, double reading, 0-8volts, and 0-40 amperes DC -$1.85

No. 35 For testing amperage ofdry cell A batteries and volt-age of B batteries (not Beliminators); double reading,0-50 volts, 0-40 amperes DC 2.00

Also Track Down Trouble in a Jiffyand Permanently Cure It with the

Aid of These Fine Meters

It is absolutely necessary to use a highresistance voltmeter in measuring the volt-age of B eliminators, either across the totaloutput or at any intermediate voltage. A lowresistance meter at least partly short-circuitsthe eliminator and causes the voltage readingto be away off. Sometimes the reading is aslittle as 25 per cent of the total actual voltage.

All "Double R" meters are accurate to 234per cent, plus or minus, and all, except theammeters Nos. 1 and 338, may be kept per-manently in circuit.

Panel meters take 2 5/64 -inch hole.

Our Complete Meter Catalogueis contained in this advertisement.

TROUBLE -SHOOTING TEST SET

High Resistance Metersfor B

Eliminators

Here is the me-ter you've beenwishing f or I A0.300 DC voltme-ter with a veryhigh resistance.Specially madethat way so it will test the output voltages,from maximum to any intermediate voltage,of any B eliminator or grid biasing resistor.It also makes all the measurements of anyother meter of its voltage range, hence willgive correct readings of B batteries, C bat-teries, cells, or any other DC voltage sourcenot exceeding 300 volts. Full nickel finish.Portable type (fits in sack coat pocket eas-ily). Accurate to 2'4 per cent, plus orminus. Fully guaranteed. Requires 35 dif-ferent dyes to make. Furnished with longconnecting cords and conven-ient tips. May be kept per- $ .50manently id circuit.No. 346

[Note: 0-500 volts, instead of 0-300 volts,is No. 347. Tests ALL power packs -Price $5.50.]

PANEL VOLTMETERFOR A BATTERIES

The best inexpensive combination for trouble -shoot-ing is a "Double R" Tube Checker, comprising a 0-10milliammeter, a 0-6 voltmeter, a switch, a rheostatand a socket. Add a high resistance voltmeter (0-300or 0-500 v.). With these it is advisable to use aplug, so that all you need do is remove a tube froma receiver that you're testing, put the plug in theempty socket and the removed tube in the socket of

the tester. You can immediately find any openor short circuits, broken or flimsy connections,

reversed connections, etc.The "Double R" Cord and Plug, andthe "Double R" Tube Checker are

shown with high resistancemeter.

SERVICE MEN!No. 210 Tube Chester, consists of 0.6 volts DC Voltmeter. 0-10 DC M1111 -

ammeter, Grid BIas Switch, Rheostat, Socket. Binding Posts (with In-struction sheet) $6.50No. 21, cord and plus. For connecting meters la A and B leads of areceiver without any disconnections. Terminals correspond with postson No. 210 tube checker $1.85No. 346 DC Voltmeter (high resistance) $4.50

No. 947 DC Voltmeter (high resistance) $5.50The cord terminals of the plug leach correspond with the binding posts of the

tube checker.Now connect the 0-900 or 0-500 volts high resistance voltmeter from Al. to

posts and you get all necessary readings. You can teat plate voltage fromB eliminators. or my other B supply. DC Plate ....sot and DC Mamma voltage.as well as the efficacy of the tube. by throwing the grid his, switch. for theplate current should change within given limits, depending on the type of tube.

MOID Your testing outfit with the indisnsable combination that constitutesthe Trouble Shooting Teat Set and Time-Sapveer. You Quickly locate trouble whileothers flounder about.Complete Combination NO,. 21 and 210 (with 0.300 Voltmeter. No. 946). 312.00Complete Combination Nos. 21 and 210 (with 0-500 Voltmeter, No. 3471..513.00

PANEL VOLTMETERSNo. 335 For reading DC volt-

ages, 0.8 volts $1.65No. 310 For reading DC volt-

ages, 0.10 volts 1.65No. 316 For reading DC volt-

ages, 0-16 volts. (65No. 337 For reading DC volt-

ages, 0-50 volts 1.65No. 339 For reading DC volt-

ages, 0-100 volts 1.75No. 342 For reading DC volt

ages, 0.150 volts 1.75No. 340 For reading DC volt-

ages, double reading, 0-8volts, 0-100 volts 2.25

One of the mostpopular meters, the0-6 panel voltmeter,DC. May be keptpermanently in cir-cuit. Panel model.

No. 326

PANEL AC VOLTMETERSNo. 351 For reading 0-15 volts

AC $2.25No. 352 For reading 0-10 volts

AC 2.25No. 353 For reading 0-6 volts

AC 2.25(See No. 348 under "Pocket and

Portable Voltmeters.")PANEL MILLIAMMETERS

No. 311 For reading 0.10 milli-amperes* DC 21.95


No. 350 For' reading 0-50 milli-amperes DC 1.65



DC PIN JACK VOLTMETERSNo. 308 For No. 20 Radiola, 0-6

volts DC $2.50No. 307 Desk type voltmeter

with cord, 0-6 volts DC 2.50

6 -VOLT A BATTERYCHARGE TESTER'

No. 23 'For showing when 6 -volt A battery needs chargingand when to stop charging;shows condition of battery atall times $US

PANEL AMMETERNo. 338 For reading amperage,

0-10 amperes DC $1.65- -GUARANTY RADIO GOODS CO., 145 W. 45th St., N. Y. City.

Please send at once your meters, catalogue numbers:

for which I will pay postman advertised price plus few cents postage.

Name

Address

City State Rip -28ALL METERS SOLD ON FIVE-DAY MONEY -BACK GUARANTY.

all 7 screen grid secrets! - americanradiohistory.com · rear view of the hbh kirplane cloth...

Documents