Vol. 9 SEPTEMBER, 1944 No. 9

CORNELL-DUBILIER ELECTRIC CORP.HAMILTON BOULEVARD

SOUTH PLAINFIELD, N. J.

CTORY

BUYUNITEDSTATESWAR

NDSAND

STAMPS

Sec. 562, P. L.&R.U. S. POSTAGE

PAIDSo. Plainfield, N. J.

Permit No. 1

Ur. L. J. 1VIo r r 1. C C

71547 North 1 . dt e

TcrldauFree, Is.

WANTED: Signal Corps Equipment

You may have Radio -Amateur and Photographicequipment that is urgently needed by the Army SignalCorps. The Army will buy the following from privateindividuals.

Radio: Standard and commercial built short wave trans-mitters (such as Hallicrafters HT -1, etc.; Temco andCollins Model 32 and 30) and Standard and commercialbuilt short wave receivers (such as Hallicrafter, National,RCA, RME, Hammarlund or Howard); AC and DCVoltmeters, Ammeters, Milliammeters, Radio FrequencyMeters and Volt -ohm, milliammeters; Oscilloscopes, 2-3inch; Audio sig. gen. 30-15,000 cycles; RF sig. gen.15-215 megacycles; late model Tube Checkers, and othertest equipment.

Photographic: 35 MM Motion Picture Cameras (suchas Mitchell (all models), Bell & Howell - Standard Pro-fessional, Akeley-Professional (all models) and Eyemo(all models) Bell & Howell Mfg.), etc., and 16 MMMotion Picture Cameras (such as Cine -Kodak Special,Magazine Cine -Kodak, Filmo 70.D or Filmo Auto Master);Tripods; Lenses, all types for 35mm and 16mm equip-ment; Exposure Meters; and Cameras (such as SpeedGraphic 4" x 5", and Speed Graphic 21/4" x 31/4" with orwithout flash synchronizers) and Leica Model III (F) or11B (C), or equal; Range Finders; Pack Adaptors andCut Film Holders.

If you have this type of equipment, you can assistthe war effort materially by selling it to the Army.Write to:

EMERGENCY RELIEF SECTIONPHILADELPHIA SIGNAL CORPS PROCUREMENT DISTRICT5000 WISSAHICKON AVENUE, PHILADELPHIA, PA.

briefly describing the equipment you have and statingthe price at which you can offer each item. FOB Phila.delphia. Do not ship any material without specificdirections from that office.

Price consideration is based upon your net cost lessreasonable depreciation for use, age, and condition ofequipment. Inasmuch as all equipment is being pur-chased FOB Philadelphia, cost of packing and shippingcan be shown separately so that an allowance for thecosts can be made when material is accepted.

Page 2 THE C -D CAPACITOR

A Free Market -Place for Buyers, Sellers, and Swappers.These advertisements are listed FREE of charge to C -D readers so if there is any-

thing you would like to buy or sell; if you wish to obtain a position or if you have aposition to offer to C -D readers, just send in your ad.

These columns are open only to those who have a legitimate, WANTED, SELL orSWAP proposition to offer. The Cornell-Dubilier Electric Corp. reserves the right toedit advertisements submitted, and to refuse to run any which may be considered un-suitable. We shall endeavor to restrict the ads to legitimate offers but cannot assumeany responsibility for the transactions involved.

Please limit your ad to a maximum of 40 words, including name and address. Ad-vertisements will be run as promptly as space limitations permit.

WANTED-Latest NRI course in good con-dition, also test equipment, such as VOM or combination set testers and tubetester. Cash at once for good equipment.Charles Lentz, 2300 Bronx Park East,Bronx 67, New York, N. Y.

FOR SALE -1 dc generator 6 or 12 vdc to350 to 700 vdc, on 6 volts delivers 350,12 volts, 700 dc, just overhauled, newbearings and brushes installed. Makeoffer, S. Wiseman, 114 N. Elmwood Ave.,Buffalo 1, New York.

FOR SALE OR TRADE -4 12" frequencyRecodes; 0-1 voltmeter. WANTED-Ra-dio testers or photo enlargers, or cam-eras. Milt Farber, 454 Ocean Ave., Jer-sey City 5, N. J.

FOR SALE -1 3Q5GT, 2 1Q5GT, 2 1H4G,2 1N5GT, I 6N5, 1 heavy duty powertransformer for car radio, 10 asst. by-pass condensers, new. 1 31, 1 A4 tubesused. First money order for $12.50 forall. Delbert Shaffner, Deepwater, Mo.

WANTED-Complete instructions for Mil-lion tube checker, model DF, either copyor photostat. Will pay any reasonableprice. Paul Sibre, 2733 S. W. 11 St.,Miami 35, Florida.

FOR SALE-Precision 700 Electronometer(comb. tube and set tester), Solar CB 1-60 condenzer analyzer, 113 v. ac -dc 2 -speed record player portable with ac -dcamplifier, also asst. radio tubes, parts,used auto radios. All inquiries answered.Raymond M. Zwickel, 1660 E. 13 Street,Brooklyn 29, N. Y.

FOR SALE - Hickok 53X dynamic tubetester. Hickok all wave signal genera-tor with built-in out -put meter. Webster60 watt amplifier with all tubes. WalterKryger, 912 W. 151 Street, East Chicago,Ind.

FOR SALE-Supreme No. 546 oscilloscope(3" very new); No. 562-A Sig. Gen. andMod. (new condition all bands); No. 550set analyzer (36 ranges incl. cond. test).Have factory instructions for all, reas-onable. T. D'ddario, 13545-117 St.,Ozone Park, N. Y.

WANTED-Test equipment to be used forradio repair shop: VOM, signal genera-tor and tube tester. Marvin Cohen, 1045Maryland Ave., Atlantic City, N. J.

WANTED-Cathode ray oscilloscope or 3"or 5" cathode ray tube. W. L. Thiel,96 Westbury Blvd., Hempstead, N. Y.

FOR SALE -2 Zenith chassis and speak-ers, 1 General Electric Mode! K32 chassisand spkr., other sets. Lours A. Gold-stone, 1279 Sheridan Ave., Bronx 56,New York.

RADIO TUBES FOR SALE - Get my listprice. Last stock of tubes were sold outin one day. New shipment arrived. V.Kozma, 3104 Wilkinson Ave., New York61, N. Y.

TRADE - Savage .22 Hi -power repeatingrifle for late issue of Sprayberry radiocourse. Want Templetone sheet fromVol. I of Rider's Manuals. L. C. Chap-man, Rt. 1, Columbus, Miss.

SEPTEMBER, 1944 Page 3

FOR SALE-Hearing Aid $10; Dayrad tubetester to 48 volts, $3.00; complete Philcoauto radio $5.00. Tauber's Radio, 516South Cicero Ave., Chicago 44, III.

TRADE 2 12" auditorium type ac dynam-ics, need new cones, have line match-ing transformers, will trade for 12SA7tubes. Can use 35L6 and 50L6. UnitedRadio and Sound Service, 71 12th St.,Wheeling, W. Va.

FOR TRADE OR SALE-Transmitting andreceiving tubes, several meters, receiverand H.V. power supply parts, quartzcrystals, 16mm movie equipment, otherradio equipment, chemicals and lab.equipment. Write for list. A. Zamba-kian, 1259 Gaylord St., Denver 6, Colo.

WANTED-Late model tube tester, multi -meter, and a set of Rider's Manuals.Walter Lyons, Darien, Ga.

TUBES FOR SALE-Most any type, no or-der accepted for less than 10 tubes, OPAlist on all tubes, send check or money,order. Refund on any types we happengo be out cf. Levenson, Suite 6, 7 Mon-roe St., Mt Vernon, N. Y.

FOR SALE-New Neo-Glo automatic elec-tric Radio Service sign. Send $2.00 fullprice, pay shipping on delivery. Alsowant a small radio, whether playing ornot. Have Sunbeam shaver, like new.Make offer. M. Levengood, Palmyra,renna.

WANTED-For cash or trade, power trans-former of 110v input of 230 or 250 ma.with 6.3 volt winding, also filter chokeof 200 or 250 ma. Want 35mm candidcamera. Have 2 band 6 tube radio withmagic eye tuning, from 5 me to 550 kc,works off one 6v battery, new tubes, Alshape. John Arnold, P. O. Box 84, Bluffs,Ill.

FOR SALE OR TRADE-Italian P. Berettapistol, .38 cal, with holster and 40 bul-lets. Gun taken from Italian officer dur-ing invasion of Sicily. Also Suprememodel 85 tube tester, Philcc signal gen-erator. Wanted: RCA Voltohmyst, Jr.,small electric drill, small radios, tubes,and any test equipment. W. S. Frank,Chippewa Falls, R. R. 3, Wis.

WANTED FOR CASH-Small radios, vacu-um cleaners, test equipment, recordplayers, cameras. G. Samkofsky, 527Bedford Ave , Brooklyn, N. Y.

FOR SALE-Hearing aid, complete withmike and earphone. Best offer takes. RCA 3 tube, 8 button Inter-com. system.Best offer takes. Tauber's Radio Shop,516 S. Cicero Ave., Chicago 44, Ill.

TRADE one used 913 cathode ray tube forphono pickup, prefer audox. WilliamMacnes, 154 Woodland, Campbell, Ohio.

FOR SALE - Have ultra -high equipmenttubes, wireless phonograph, etc. Want8 mm movie projector, home recorder,crystal mike, vibra -pack. W. M. Mc-Donald, 933 Main St., Melrose 76, Mass.

SWAP-Simpson 0-200 ma dc meter in Alshape plus cash for an 0-1 ma dc meterof reliable make and in similar condi-tion. W. E. Percel, 2315 Caledonia St.,Toledo 5, Ohio.

FOR SALE-Maytag two cyl. gas engine,32 v. Philco cabinet radio also others,2 late model battery farm radios.WANTED-Medalist Kodak camera, Jun-ior Voltohmist RCA, Ampso 16mm soundprojector, model X or XA. F. Miller, 208Linden Ave., Woodlynne, N. J.

WANTED-Late model signal generatorin good condition. Write Auburn RadioService, 829 Park Ave., Cranston 10,R. I.

FOR SALE-Tubes and parts. SupremeDiagometer, Supreme sig. gen., VTVMtube tester, other tester, new phonomotor ang table. Cash only or sellwhole shop. Crooks Radio Service, Box94, Kent, Ohio.

WANTED-Modern tube checker; also alate model signal generator. Write stat-ing make, condition and price to Harry'sRadio, 7 School St., Glen Cove, L. I.,N. Y.

WANTED-Reel for lake fishing-Pfleugeror Shakespeare preferred, or any goodmake-must be in good condition. Cash.Bert Buckner, 280 W. Central, Si. Paul 3,Minn.

FOR SALE-Home built volt OHM meter.Jewell 135 foundation meter-ten dollarscash. Oscar's Radio Service, Merrill,Iowa.

SALE OR TRADE - Teleplex Jr. Codemach. with five tapes and built in ACoscillator, new Triplett 221 0-10v DCVM. WANT "Kirsten Pipe" recorder,two speed, Pvt. J. C. Terribilini, SignalCo. SCU 1991, Presidio of San Francisco,San Francisco, Calif.

FOR SALE - Model 85 Supreme tubechecker with adapters, $20; Thordarsonoutput trans. T15S92, new, $18; Thordar-son driver trans. T15D85, new, $9.60.Thordarson choke T75C51, new, $6;Rider's manuals 1 & 3, ea. $5; ElectricService sign, $3. Clair E. Breth, Sr.,213 S. 4th St., Youngwood, Pa.

(Continued on page 11)

Page 4 THE C -D CAPACITOR

SERVICING L. F. AMPLIFIERS *Fundamentals of Audio Amplifier Stages. FrequencyResponse Characteristics and Gain Calculations

Low frequency amplifiers are de-signed to increase small voltages inthe audible frequency range of ap-proximately 16 to 18,000 cycles persecond, obtained from microphones,electric phonograph pickups, the de-tector stage of a radio receiver, andother devices. In communicationwork these low frequency amplifiersare called audio amplifiers and thesetwo terms will be used interchange-ably. The amplified voltage is usu-ally applied to a loudspeaker or other

venting the direct plate voltage ofone tube from disturbing the gridbias of the next tube, and yet it mustpass the signal current with a mini-mum of modification of amplitudeand phase as the frequency changes.The positive plate voltage on the firsttube, possibly several hundred volts,must not be applied to the successivegrid which is essentially negative,both being measured with respect tothe B- or "ground."

USUALLY PENTODE

CH/5515 5-RESISTANCE-CAPACITANCe COUPLING

yOiN MIDDLE I HIGHFREQUENCIES

LOSS DUETODECREASING

CTL

I -INCREASINGOSSDUETO XCC

IDO 8000FREQUENCY

Fig. 1. Typical resistance -capacitance coupled amplifier showing frequency responseand effect of circuit components. C.I. is stray wiring and Miller effect capacitances.

device to convert electrical energyinto mechanical energy.

Low frequency amplifiers usuallymust be capable of uniform gain overall or some portion of the 16.18,000cycle band. The uniformity of gainwith frequency is primarily a func-tion of the type of coupling betweenthe stages of tubes.

One essential detail that must beaccomplished by any system used incoupling the output of one tube tothe input of another is that of pre -

Audio stage coupling systems in-clude iron core transformers, resistor,capacitor combinations, and inductor -capacitor combinations. All of thesewill ordinarily produce frequencydistortion of the signal to some de-gree. It is necessary to study eachproblem as to the best couplingmethod to use.

The conditions for perfect trans-fer of signal current from one stageto the next are: Faithful reproduc-tion of all frequencies present in the

* Courtesy of Radio and Television Retailing.

SEPTEMBER, 1944 Page 5

original signal, without altering thewave shape; Magnification of theamplitude of the signal in a linearmanner. The principal types of au-dio coupling methods and their gen-eral frequency response characteris-tics are shown in Fig. 1, Fig. 3, andFig. 4.

In some problems, there is a neednot only to amplify the signal butto modify it in some pre -arrangedmanner, giving another problem tothe design of vacuum tube amplifiers.

R -C Coupled Voltage AmplifierThe use of tetrodes and pentodes

is a practical means for getting asimple voltage amplifier at lower costand weight, and under usual condi-tions, with less frequency distortion,than those using transformers forcoupling. A typical circuit in Fig. 1

shows a capacitor for coupling theplate of one tube to the grid of thenext, and high -value resistors forplate and grid circuits. The couplingcapacitor, CO, is sometimes called ablocking capacitor since it offers avery high impedance to D.C. This

coupling system is often designatedsimply resistance coupling.

Since the alternating voltage mustappear across the following grid re-sistor Re, there is provided a cou-pling capacitor Cc which offers lowimpedance to signal current throughthe grid resistor Ra. The followingtube also has an input capacitancewhich is in shunt with its own gridresistor. This input capacitance, CT,is a parallel combination of the inter -electrode grid -cathode capacitance andthe Miller effect capacitance. Thusthe effective load on the first tubeconsists of a combination of the tube'sown internal plate resistance R,,, theplate load resistor RL, the grid re-sistor R5, the coupling capacitor Ceand the next tube's input capacitanceCr. The equivalent circuit is shownin Fig. 2.

The voltage gain of a resistance -capacitance coupled amplifier stage isnever equal to the "µ" or amplifica-tion constant of the tube. The plate -circuit alternating voltage is dividedbetween two impedances in series.One of these is the plate resistance,

EQUIVALENT CIRCUIT

APPROXIMATE CIRCUIT FOR°LOW" FREQUENCIES

IT= -Gm Eg

1111 Rg Eo

APPROXIMATE CIRCUIT FOR"MIDDLE" FREQUENCIES

IT= -Gm Eg

RP R1E

TCTAPPROXIMATE CIRCUIT FOR

HIGH FREQUENCIES

Fig. 2. Equivalent circuits for resistance coupled amplifiers at middle, low and highfrequencies showing active components.

Page 6 THE C -D CAPACITOR

of the tube itself. The other isthe combination of the load resistanceRL, the grid resistor Re, the cou-pling capacitor CO, and shunt capac-itor CT.

At medium and low audio fre-quencies the tube's input capacitanceCT is not important, since its react-ance is usually greater than Re,while C, can readily be chosen ofsuch a size that the voltage dropthrough it is small. The load is thennearly pure resistive and the gaincalculation becomes:

cc = Voltage gain - G"'

GP+Gj.+GgWhere Gm is the mutual conductanceof the tube in mhos (this value isusually listed in micromhas which is10-8 mho.), Gn is the tube's plateconductance (1/R,), GL is the con-ductance of the plate -load resistor(1/R1,), Gg is the conductance ofthe grid resistor (1/Ro).

At low audio frequencies (say be-low 100 cycles) the reactance of thecoupling capacitor Ce begins to causea considerable voltage drop, since itis in series with Ra. The equivalentcircuit is shown in Fig. 2. For ex-ample at 60 cycles, with a couplingcapacitor of 0.011 ,G,f and a grid re-sistor of one-half megohm only 90%of the voltage is effective betweengrid and cathode. If the same per-centage is to apply at 30 cycles, C,,must have twice the capacitance. Itis not desirable to increase Cs muchbeyond the actual low frequency re-sponse requirement for three reasons,(1) the amplifier stability becomesless, (2) a physically larger capacitorincreases "hum" and noise pickupand (3) the leakage of DC to thegrid increases. However, if severalstages are to be used it may be neces-sary to go farther in the matter ofsecuring "flatness" in the frequencyresponse curve since the deficienciesof the stages are multiplied by cascad-ing. Thus if a stage gain drops 20%at 60 cycles (response 0.8) thenthree such stages will respond (0.80)=51% of middle frequency gain.

The gain at low frequencies iscalculated by the process of applyingcorrection factors to the gain calcu-lated for the medium frequencies.These factors may be found in anumber of standard texts.*

At high frequencies C,, may be ig-nored because of the decreasing react-ance but Cr assumes increasing im-portance and eventually becomes thedominant factor so that a plain re-sistance -coupled amplifier gives lit-tle gain above approximately 50,000cycles. The lower gain is due to thedecreasing reactance of the inputcapacitor CT which is shunted acrossRe. The equivalent circuit is shownin Fig. 2. For any tube, the inputcapacitance does not have only thesmall value listed as the grid -cathodecapacitance but instead:

Input CT = Ggk -}- Co, (1 + «)For a typical amplifier using a 6F5high ,u, triode,

Input Cr=5.5+2.3 (1-70)=160 u,µf (maximum).

While tetrodes and pentodes haveCg values of about 1/1000 that ofsimilar sized triodes, the stage gaincc is greater also. In general thetotal input capacitance CT will belower than for triodes.

The gain of the resistance -capaci-tance amplifier is less at low fre-quencies (under 200 cycles) and athigh frequencies (over about 8,000cycles) than at middle frequencies(1,000 to 4,000 cycles).

The voltage gain of an amplifierstage is best shown by example. Theproblem is to determine the amplifi-cation of a 6J7 pentode with resist,ance-capacitance coupling. The tube'sGm = 1,200 micromhos, plate resist-ance Rn = 1 megohm, (these arefound from a tube data book). Thecoupling device consists of a plate -load resistor Rr. = 250,000 ohms, agrid resistor of 500,000 ohms and acoupling capacitor of 0.01 J.

*The Electronic Engineering Handbook-Caldwell-Clements.

Radio Engineering-McGraw-Hill.

SEPTEMBER, 1944 Page 7

The next step in using equation(1) is to determine the correspond-ing conductance. The plate resistanceof 1,000,000 ohms (10°) has a con-ductance of 1/100 or 10-° mhos. Theplate -load resistor value of 250,000ohms gives 1/250,000 or 4 x 10'°mhos and the one-half megohm re-sistor Rg, a conductance of 1/500,000or 2 x 10-6 mho. These conductancesare in parallel (see Fig. 2) henceadding them gives the total conduct-ance of 7 x 10-° mho. To find the

them by iron -cored inductors. Usu-ally only the plate resistor is so re-placed and the arrangement may becalled an impedance -capacitance -re-sistance coupling or simply an im-pedance coupling. The frequencyresponse is inferior to that ofresistance -coupled amplifiers. Typicalcircuits and response curves areshown in Fig. 3. The decrease ingain at high ;requencies is greaterbecause chokes have more distributedshunt capacitance than resistors. The

USUALLY TRIODE

L -C -R OR IMPEDANCE COUPLING

o4Jo

TRIODE USUALLYBUT MAY BEPENTODE ORYETRODE

B -DOUBLE -IMPEDANCE COUPLING

EFFECT OF RESONANCE[IN LG AND CD

LOSS DBE TOLOSS DUE TO # DECREASINGDECREASING XL XCSa INCREASING XCC

100 5000FREQUENCY- CYCLES/SECOND

Fig. 3. Impedance coupling gives frequency response similar to resistance couplingexcept where grid choke is used. Resonance in Co and Lo give low frequency rise

in amplification. Rise may be controlled by shunting resistor across LG.

middle -frequency voltage gain it isnow only necessary to divide thetube trans -conductance (G,,, = 1200micro -mhos = 1200 x 10-° mhos) bythe sum of the circuit conductance(7 x 10-6 mhos).

1200 x 10_o mhos«- 7x10'Umhos =171

Impedance -coupled AmplifierAn obvious way to avoid the direct

voltage drops in the resistors of anR -C coupled amplifier is to replace

decrease in gain at low frequencies isgreater because the inductive react-ance falls with frequency while re-sistance does not. The arrangementis used less since tubes suited to re-sistance coupling have become avail-able. Impedance coupling is usedprimarily with triodes where therelatively high plate current makesthe use of load resistors costly sincea large power supply voltage wouldbe required.

If both plate and grid resistors arereplaced by chokes, "double impe-

Page 8 THE C -D CAPACITOR

dance" coupling results as shown inFig. 3. Since two chokes are thenin parallel (for AC) the high fre-quency decrease is accentuated but alow -frequency rise can be producedby choosing the two chokes and thecoupling capacitor to produce seriesresonance at the low end of the de-sired range. A desirable type of lowfrequency rise results if the coils arechosen so that their Q is between 1

and 2 at the resonant frequency.The gain at the resonant frequencyover and above the ordinary middlefrequency gain of the stage is about

design principles. A typical trans-former coupled amplifier is shown inFig. 4.

Using a well -designed transformerfor the medium frequency range theClass A gain of a transformer -coupledstage is nearly:

(sec. turns)gain cc =11 (primary turns)

i.e., the tube gain multiplied by thetransformer gain. It is correct onlyif the primary reactance is large ascompared to its resistance and to theplate resistance of the tube. Conse-

INPUTTRANSF.

INTER - STAGECWTRANS.

4I--'/ OUTPUT ZTRANSF.

Go c9_

WJ t7

H

B

CBJ>

-A --LOSS DUE TODECREASING -XL

200 3000FREQUENCY

Fig. 4. Transformer coupling showing stray inter -winding capacitances. Curve A istypical of cheap transformer while B is for high grade type.

1 DB for Q = 1; 3 DB for Q = 1.4;and 6 DB for Q = 2. It is neces-sary that the plate -circuit coil have areactance 3 or 4 times as great as theplate resistance for good response.

Transformer CouplingThere are several advantages in

audio transformer coupling. Thereis a negligible drop in plate supplyvoltage through the transformerwindings, hence the "B" supply volt-age may be moderate. The DC gridcircuit resistance can be very smallwhere an input transformer is used.This is an advantage with certainclasses of power amplifier operation,particularly Class B. Since suchcoupling devices can be purchasedready-made the frequency response inconsiderable part depends upon theobservation of general transformer

quently equation (3) holds true formedium frequencies but fails at lowfrequencies because the transformer'sprimary reactance falls. The decreasein amplification is related to the re-sistances just mentioned, and thetransformer's low frequency responsecurve can be predicted if there isknown: the tube's plate resistance(tube data book) and the resistance(R,) of the transformer primary,and its inductance (L) with the sec-ondary open such as might be meas-ured on a bridge. It is to be notedin Fig. 5 that the effect is most pro-nounced in a transformer (Curve 1)whose secondary is unloaded, or con-nects to an extremely high resistancesuch as a Class A grid circuit. Ifthe load resistance (as R in Fig. 4)equals the source resistance, RI, +primary R,, (Curve 2) the low fre-

SEPTEMBER, 1944 Page 9

quency loss is less. Finally with aload whose resistance is much lessthan that of the source (Curve 3)the low frequency loss is small. Thisis observed in a practical way in therelative small size and cheapness ofClass A output transformers feeding

6

6

,LO 0 R*OP SOURCE R,.-LC.0 : i(d. S -INFINITE LOAD SUCH

AS CLASS A, GRIDAT LOW FREQUENCY.

S N 6PATIO OF PRIMARY REACTANCE TO

(TUNE PLATE CIRCUIT R0+ TRANSFORMER PRIMARY RI)

Fig. 5. Low frequency response charac-teristics of transformer for various plateloads.

low impedance loads. Conversely,if two transformers be equally welldesigned, one as a "plate -to -grid"transformer, shown as solid curvesC and D of Fig. 6, it will producea curve dropping off more at thelow end than the corresponding"plate -to -line" or "line -to -line" trans-formers shown by the dashed curvesin Fig. 6.

This situation is aggravated if thetransformer is made too small, as inthe case of the curves for a cheapexample, Fig. 6, Curve A. Occasion-

ally this kind of thing is done de-liberately to create a transformerwhich is peaked at some particularfrequency that must be amplified.Curve B, Fig. 6, is for a transformerexactly like that with Curve A ex-cept that a trifle over one-half of theprimary has been removed, the pri-mary reactance thus dropping toabout one -fifth of its former value.Lack of amplification at low fre-quencies is now very apparent. Thetransformer becomes a very poorload for the tube except for thatfrequency to which it is tuned by itsown inductance and the capacitancesin the circuit and that of the trans-former itself.

The high frequency drooping ofthe gain curve is due to the shuntingeffect of the capacitances within thetransformer and in the circuit. Theuser of the transformer can do verylittle about this, but the maker of thetransformer can (and usually doesin the case of high grade transform-ers). Thus in the solid curve C ofFig. 6, for the high -quality broadcastservice transformer there is a reso-nance peak at 10,000 cycles, producedby tuning the transformer inductancewith the capacitance of transformerand circuit to 10,000 cycles. Herethe leakage inductance is referred to,obtained by measuring the primary'sinductance on a bridge with its sec-ondary short-circuited. That this isthe actual cause is shown by thedashed curve in C for a similar trans-former working into 500 ohms. The

-r*211/f21190.11~®1 t] -2

®KTA1111111®,® ` . ; ------^------'-----.- z ¢ i .; C- HIGH DUALITY BROADCAST TRANSFORMERS

gó

'

+9 ..

' , .111'1

_QUALITY"°® U HIGH FACSIMILE TRANSFORMERS10 Kra .: I000 3.10000 XX1,000 WITH EXTENDED HIGH -FREQUENCY RANGE

Fig. 6. Response characteristics of several types of audio coupling transformers.Design of unit is major factor in high fidelity equipment.

Page 10 THE C -D CAPACITOR

10,000 cycle rise by resonance, can-not take place with only a 500 ohmload. Similarly the solid curve Dshows a resonance which has beenmoved out to 30,000 cycles by di-minishing both the capacitance andthe inductance of the transformersecondary. In the absence of thishigh frequency "bump" the curvesimply droops in the permanent man-ner of the dashed curves.

THE RADIO TRADING POST(Continued from page 4)

URGENTLY NEEDED - By service manSX28 Hallicrafter. Send price and detailsto Pvt. J. Leonard King 970812, 2nd Trng.Bn., Co. B., Inf. Trng, Reqt T.C.-F.M.F.,Camp Pendleton, U.S.M.C., Oceanside,Calif.

WILL TRADE- Model 582 Supreme signalgenerator for a late model Royal orCorona portable typewriter in goodcondition. Rural Radio Service, ClarkLake, Mich.

WANTED-For cash or trade-Jensen JAP-60 or JHP-52 speaker unit. Have largequantity P. A. equipment incl. largeJensen speaker units. Write for list.Also have good used Precision model 500Electronometer for sale. Kenneth Law,312 West Third St., Fairmount, Ind.

FOR SALE-Philco auto radio model AR75with instrument board speaker, $50.Also tested used tubes, 60% off. OOA,01A, 24, 26, 27, 37, 38, 50, 58, 81, 71A,6A3, 6L6, 6N7, 6Q7, 99. Add postage.H R. Ringold, 132 N. Doheny Dr.,Beveily Hills. Calif.

FOR SALE OR TRADE -1 to 4 vols ofOfficial Service Manual, good condition,$12. 5, 6 Rider's, like new, $12. WANTgood VOM meter or analyzer and 0-1mil. 3" Bedee meter, state price. V. D.Walker, 716 North St., Pittsfield, Mass.

WANTED-New or used Emerson or othermake camera type portable radio ingood condition. State Price. Frank A.Witkowski, 32 Daymond St., Trenton 10,N. J.

FOR SALE -6v tubeless vibrack 100 .22long cartridges. headphones, 100 usedfixed resistors, Jacobs chuck 1/8 to5/8, ac -dc jig saw, new tubes, 26,57, 2B7, 79, BH, 10 mixed i.f. trans., 3mercury switches, single button .Hiketrans., 6v relay, 20-0-20 DC c'.,,,eremeter. All $38. Radiotrician, 2748 i..eadeSt., Detroit 12, Mich.

FOR SALE-Complete Jr. Mobile Tele-vision unit consisting of Iconoscope,relay monitor and 2 receivers withpower supply, Cathode Ray tube andshielded cable, quick -set Television cam-era tripod. Best offer takes it. SamuelM. Mack, 141 Summer St., Lowell, Mass.

SELL OR SWAP-Simpson 333 tube checkerin excellent condition, neon short check-er, Bosch car radio, $92.55 worth oftubes. All for $85 or will swap forcommunications receiver, tiallicrafterspreferred. Don Flaig, 3806 John St.,Fort Wayne 5, Ind.

WANTED-Record player, wireless type.State condition and price. Tom Dugan,163 Nichols Ave., Syracuse 6, N. Y.

FOR SALE-Six pieces radio testing equip-ment, $200. 135 new tubes (mixed num-bers), quantity new parts, manuals,$250. No split up. Cash or trade forwhat? W. S. Crooks, Box 94, Kent,Ohio.

WANTED - Signal generator, CloughBringle OC or OCX and tube and settesters, Supreme 599 or Radio City pro-duct 802A. Floyd Morris, Appomattox,Va.

FOR SALE -2 giant Flacon Electrodynamichorn units, 5 Master Electrodynamicunits all with good diaphragms, sellall for $100. Daidone Radio ServiceLaboratories, 762-4-6 South Orange Ave.,Newark, N. J.

WANTED-Batt. charger, 3 or 10 amp.bulb type preferred. Others considered.State size and price. Clarence W. Hull,Mineral Springs, Pa..

FOR SALE - Webster DeLuxe recordchanger, changes 16 records, 3 poststreamlined loz. permanent pickup, lastmodel made, like new, $95. Meissner 8tube F.M. tuner, little used, $48. Brandnew Asiatic model 30Y mike, $25. M. A.Porter, 1713 Larrabee St., Chicago 14,Ill.

FOR SALE-Western Electric model 18receiver, 30 to 40 megacycles. 110v ACor 6v dc 7 cubes superhet with squelch.A-1 condition. James Lawless, 496 Pleas-ant Valley Pkwy, Providence 8, R. I.

WANTED-Ampro or Bell & Howell movieprojector 16 mm. sound. Must be inworking condition. Cash paid. Send forinspection now. WILL SELL, New stock10w resistors, condensers, volume con-trols, lw resistors, other parts all newfor $225. Send M.O. Anchor SupplyService, Box 482, Ithaca, N. Y.

SEPTEMBER, 1944 Page 11

WANTED -900-0900v 500ma plate trans.,400-0-400 (450v) 300ma plate trans., 5-20500 ma Swinging choke, 300 ma swing-ing choke. Frank W. Jones, Gabbs,Nev.

FOR SALE OR TRADE -Parts of everydescription. Write for list. Carl A.McKay, 2315 Springfield Avenue, FortWayne, Ind.

FOR SALE - GE reactor, 13 henries, 600mils, 220 v. Two type 601 GE transf.,pri. 100-200 v., sec. 15/12 and 7.5/6 v.American transf. 1.5 KVA, pri. 110-220,sec. 1100/2200 v. All 60 cycles. Cheap.M. J. Nederostek, 848 Walnut St., Allen-town, Pa.

FOR SALE -New tubes, list price less 40%Nos. 58, 6c6, 78, 56, 38, 12Z3, 77, 6B7, 31,6D6, 2A6, 76, 2A5, 35, OZ4, 39, 89, IT4,7H7, 7C7, 7E7, 12B8. Mostly 1 to 6 of akind. K. Petitt Radio Service, Thebes,Illinois.

FOR SALE -1 Racon 4.5 horn, 2 Raconhorns with 12 in. cones, 2 Atlas hornsfor 12 in. cones, Aerovox 75 bridge, Su-preme 550 tester, Oxy-acetylene weld-ing outfit. Leo L. Bowman, 615 W. MainSt., Lewistown, Montana.

WANTED -Superior Dynarometer with 81/2in. meter made in 1940. Also Superiormodel 1240 tube tester and model 1230signal generator. A. J. Talbot, 2334 FirstAve. N.E., Atlanta, Georgia.

FOR SALE -Weston meters, model 301,476 ac, Superior Dynarometer, 1260 mod.,Philco recording arm corn. with trainmod. HR2, Superior channel analyzer,Meisner Television with FM sound. Fourbands complete, less cabinet, Al condi-tion. NEED C -D Capacitor Analyzer BF -50. Cherrill Radio Electric, 4235 E. Bar-nett St., Philadelphia 35, Pa.

FOR SALE - Stromberg-Carlson model 69all wave selector, 3 bands, 1430-4200kc, 3.7-10.5 mc and 9-25 mc, including6D6, 6A7, 76 and 84 tubes, $15.00 f.o.b.St. Louis. Adolph Hoefer, 21 Lee Ave.,Clayton 5, Mo.

FOR SALE -Tubes, 1A7G, 1N5G, 1H5G,1C5G, 12SA7, 12SQ7, 35Z5, 35A5, 45, 6F6,6K6G and many other scarce ones.WANTED -Good 8mm movie camera andprojector, condenser tester, signal gen-erator, RCP 446 multimeter and goodanalyzer. Will pay cash or trade. J. M.Fraser, Binscarth, Manitoba, Canada.

WILL TRADE -Small model makers metallathe with independent chuck, faceplateand drill attachment like new; for out-board motor in good condition. Or willpay cash. All letters answered. V. D.Telschow, 205 So. W. 1st St., Red Oak,Iowa.

FOR SALE -Business interests, radio andappliance franchises, including equip-ment, stock of accessories and tubes.Ideal location for money maker and fu-ture for right man, who wants to makegood. Same location 17 years. Getready for postwar business. Paul Apple-gate, Ansonia, Ohio.

TUBES FOR SALE -Price 50c each, 71A,35, 26, 24A, 27, 80, 37, 38, 39, 55, 57, 58,33, 6E7, 6B7, 199, 89, 31, 200A, 201A, 2A7,2B7, 2A5. All are OK, mostly brandnew. Hundreds of burned out tubes 5ceach. Millhurst Radio Service, Free-hold, N. j.

FOR SALE-1SA6GT, 1SB6GT tubes. Alsodo you need 12, 25, 35 and 50 volt. Ifso send 50c for details on how repairthose burned out ones with your presenttube tester. L. M. Wycoff, Box 133, Mar-maduke, Ark.

FOR SALE -No. 800 Segal key cutting ma-chine, only needs a new cutter. WILLTRADE Jewell model 540 tube tester, incase, A-1 shape for condenser tester.Highest offer takes either one. Apex Ra-dio and Electrical Shop, 4228 Green-wood Ave., Chicago, Ill.

FOR SALE -1 RCA Rider Chanalyst likenew, used few hours $107.50; DuMont164 3" oscillograph never used, $65.00;1 slightly used 2 speed turntable withfine crystal pickup, gear driven motor,$50. V. F. Daidone, 762-6 South OrangeAvenue, Newark, N j.

SELL OR EXCHANGE -Parts, radios, guns,locks, sewing machines, keys. Shoe re-pair materials. Walnut, woods, miner-als, violin, handmade knives. Tools,screws, bolts. Hobby goods. GenevaTolley, 217 East Broadway, Clayton,New Mexico.

WILL SELL -Custom-built 21/9 meter trans-ceiver having 6J5GTX, 615GT, 6L6, SW4,Federal anti -capacity switch, Thordar-son transformers, milliammeter, handwheel dials, nameplates, chrome trimcabinet, ac operation, sell for cost ofparts, $25. New Shure crystal handydesk mike, $6.50, DeJur Critic exposuremeter for stills, $17 50. L. F. Carini, 246Wolcott Hill Rd., Wethersfield, Ct.

URGENTLY NEEDED - 12SA7 and 35L6tubes, will pay full list price OPA, anyamount one to 25, have many sets be-longing to service men needing thesetubes. United Radio & Sound Service,71 - 12th St., Wheeling, W. Va.

WANTED -All kinds of radio tubes for afair price, please send list of quantityand price. Radio Maintenance ServiceCo., 841 South Vermont Ave., Los An-geles, Calif.

Page 12 THE C -D CAPACITOR

FOR SALE-One each Precision 700 and900 portable set and tube testers, SolarCB -1-60 condenser analyzer, Dumont 164oscilloscope, Radiart P6 vibrator tester,Precision E 300 signal generator, 110 v.ac -dc, 33 1-3 and 78 rpm record playerand amplifier in leatherette carryingcase, Emerson cabinets to it 301 and336 radios. Signal Radio, 2077 ConeyIsland Ave., Brooklyn 23, New York.

WANTED-Supreme 599 or Weston 774 orother good late model combfnat'on. Willpay your price. Also need 50L6s, payyour price. J. W. Krouse, 1787 Oak -mount Road, So. Euclid 21, Ohio.

WANTED-Sunreme 504A portable lab. orHickok 510X dynamic mutual conduc-tance tube and set tester. Must be inA-1 condition, complete. O'Bnen's Ra-dio, 609 W. 1st, Fulton, N. Y.

FOR SALE-Used tubes for all radios fromwhen they started to make radios to1936. Good condition and law price.Pete's Radio Shop, 405 Bridge Street,Lowell, Mass.

WANTED-Cash waiting for your Superiorsignal generator $15.00 for the first toreach me by express. Urgent. Notify meof your shipm i ''.n :2vance. Lyons Ra-dio Service, 5/06 S. Marshfield Ave.,Chicago, Ill.

WANTED-Back issues, Wireless Engineer,Electrical Communications, Phillips Tech-nical Review, Electrical Engineering,Journal I.E.E., G.E. Review. GroteReber, 212 W. Seminary St., Wheaton,Illinois.

FOR SALE-Weston A.C. voltmeter, model476, 0-150 v. scale. Perfect condition.Make offer. L. West, 93 Monticello Ave-nue, Jersey City 4, N. J.

FOR SALE-Tube tester, set tester, signalgenerator, Rider's Manuals, good stockof tubes and parts. Write for detailsM. W. Raybon, Conover, N. C.

WANTED-A grateful sailor would appre-ciate a copy of Mathematics for Elec-tricians and Radiomen by Cooke, andpublished by McGraw Hib Co. Canyou spare me one? I Henry Heyer,Sl/cRT, Co. 388, U.S.N.T.C., Sampson,New York.

FOR SALE-Triumph cathode ray oscillo-scope, mod. 830, 3" screen, hardly used.Carl Schradieck, 65 Hazard Avenue,Providence 6, Rhode Island,

WANTED-Good grade condenser check-er. No. old timers. Quote make, model,condition and price. Martin Radio Ser-vice, 142 Ralph Ave., Brooklyn, N. Y.

FOR TRADE-Howard mod. 460 communi-cation receiver, A-1 condition, completewith 13 tubes, preselector, loop kit, xtal,etc. Want Hickok RFO-5 scope. Earl D.Kent, Mountain Home, Idaho.

FOR SALE-Complete Hickok radio lab,A-1 shape: mod. 155 traceameter, 19Xcrystal control microvolt generator, RFO5 oscilograph, 2105 zero current volt-meter tester, end cols, lamps, reflec-tors, de luxe work bench and Rider'svols. 3 to 13 inclusive. Price $1,000.00f.o.b. Laredo, Texas. Radio Service andSupply Co., 1219 Lincoln St., Laredo,Texas.

FOR SALE -150 new tubes at list prices,about 70 tested used tubes, many con-densers, resistors, and parts. New phonomotor and table $20; Burton Rogers tubetester, mod. 21, $15; VTVM $35. SupremeDiagometer 585 $80; Supreme signal gen-erator 371 $45; Superior tester 1280 $21;output meter, 8" meter $25; 2 small ra-dios $19 each. W. S. Crooks, Box 94,Kent, Ohio.

FOR SALE-New radio tubes in originalcartons at 40% off, 10, WD -I1, 12A, 31,40, 89, X99, 1E7, 1B4. Torrence Radio,2012 Madison Ave., Toledo 2, Ohio.

FOR SALE -3 battery sets complete withtubes and spkrs. 1 S.M. original 8 -tubeac with tubes and dynamic. 1 Tungarand 1 Rectox trickle charger. Best offerfor any or all. Ray Decker, 119 PineSt., Portland 4, Maine.

FOR SALE-Superior Sig. generator, modelG.N.T. 6 bands from 100kc to 2200 kcand 2.2 me to 105 kc AF and RF Audiofrequency from 25 to 10,000 cycles. $35.John E. Thiel, 742 N. Denver, Tulsa 6,Okla.

WANTED-Rider Manuals 1, 2, and 6 to 13.Top prices for one or all. Also Simpson0-1 Ma. model 27 meter scale for V.O.M.meter. John E. Thiel, 742 N. Denver,Tulsa 6, Okla.

FOR SALE-Tubes-200 in sealed cartonsand 200 perfect tubes unboxed. Tubesin cartons at OPA list. Unboxed tubes30% off. Send for what you need withcheck or money order. Refund on any-thing we have not in stock. Mason Radio,114 E. 3 St., Mt. Vernon, N. Y.

WANTED-For Cash-Hallicrafters S-29; orany good communication receiver whichhas provision for 6v portable operation.All letters answered. Kenneth Walker,LaCygne, Kan.

WANTED-Riders Service Manual vol. 6.Modern Radio Servicing by Ghirardi.Servicing by Signal Tracing. Must becomplete and in good condition. Clar-ence W. Hull, Sr., Mineral Springs, Pa.

SEPTEMBER, 1944 Page 13

SELL OR TRADE - Clough Brengle OCAall -wave Signal generator. Dayrad Ray-theon 92 tube tester; Potter model Acondenser tester; Mallory 3 amp batterycharger; Race motor hair clippers, 3Afolding camera. Glenn Watt, Chanute,Kans.

FOR SALE -Sun lamp; vibrators; electricbelt and radios. August Engfer, 715AW. Scott St., Milwaukee, Wis.

TRADE -5" Tripplett VOM in box for sig.gen. AC or DC. Also want instructionsheet "How to Make 9 Basic Tests withSuperior Channel Analyst." Need allkinds of test instr., tubes. Send prices.L. Olsen, 60171/4 Sunset Blvd., Los An-geles 28, Calif.

FOR SALE - Miscellaneous tubes andequipment. Write for list. Fred Craven,2216 S. 7th St., Phila. 48, Pa.

FOR SALE -Radio tubes, new, postpaid26, 27, 35, 24A, 6Y5, 6A75, 32, 37, OlA,6Q7G, 551 and P2 types -one ea. avail.E. L. Freeland, 48321/2 W. Madison,Chicago 44, Ill.

WANTED-T.R.F. Hi -Fidelity tuner, pre-ferably Miller, in kit or assembled. AlsoBogen P.V-20 amplifier and MeissnerSignal splicer. State lowest price andconditicn. R. A. Brewer, Box 107, Frank-lin Village, Mich.

FOR SALE -Assorted radios and chassis.Write for list. Louis A. Goldstone, 1279Sheridan Ave., Bronx 56, N. Y.

WANTED -Hook-up for 318 -Atwater -Kentradio. Must be for this particularmodel. Write to Frank Johnson, 320Orchard St., Oil City, Pa.

HELP WANTED -Excellent permanent pos-ition open as Laboratory Technician toany C -D reader, male or female offeringsuitable qualifications. Apply by letteronly. Mr. C. T. Martowicz, c/o H. L.Crowley & Co., 1 Central Ave., WestOrange, N. J.

WANTED -Good tube tester and capacitoranalyzer. Price and condition in firstletter Thomas L. Siglin, 427 Wayne Ave.,Oakland 6, Calif.

WANTED - For cash-Hallicrafters shortwave receiver. Prefer the "Sky Champ"model or what model have you. Pleasegive details in first letter. C. N. Cheadle,315 Y.M.C.A., 3210 Arthingion St., Chi-cago 24, Ill.

FOR SALE OR SWAP -For what have you.1T4, 106, 1A6, 19 12SN7, 22, 31, 32, 48,49, 1J5, 12A5, 10, etc.Joseph F. Happle,110 McGuire St., Oneida, N. Y.

FOR SALE -New G.I. Recorder -playbackunit -2 speed in original carton, $45.2v Porta -Power pack -Model L, $12.Used Western Electric an damped pick-up mod. 4A, $8.50. Utah PM trumpetunit 25w 15ohm V.C. F.O.B. M. A. Porter,1713 Larrabee St., Chicago 14, Ill.

FOR SALE-Astatic mike mod. J-30, $17.50Astatic mike mod. IT -30, $15. Both new.M. A. Porter, 1713 Larrabee St., Chicago14, Ill.

FOR SALE -Oscilloscope, Clough BrengleCRA 3", also Supreme 560A Vedolyzer.Eddie, 1724 Central, Middletown 6, Ohio.

WANTED - Test equipment, tubes andparts, for both receivers and transmitters,also electric motors. All must be newor near new condition. Courtney RadioLabs., 4522a San Francisco Ave., St.Louis 15, Mo.

WANTED - RCA, GE, DuMont or otherTelevision sets in any condition. Elec-tronics Service & Supply, 264 W 40thSt., New York 18, N. Y.

WANTED -Air Mail stamps of any country(used). Also British Colonies (used).Send cat. No. and lowest price. Ben-jamin Pomerance, 2835 Bedford Ave.,Brooklyn 10, N. Y.

FOR SALE -New RCA 800 tube; newRCA 814 tube; two Taylor T-55, used,but good; Eimsc 75T used. all for $25fob. Wm. Worland, 606 Martin St.,Greenville, Ohio.

WANTED - Television receiver. Preferlarge screen. State make, mod. no.,condition and price. Jack's Radio Ser-vice, 296 Wainwright St., Newark, N. J.

WANTED -One dozen Rola G-12 DynamicLoudspeaker units with or without conesand transformers, but with a 1500 ohmfield coil. Paul H. Thomsen, 903 Phila-delphia Ave., Silver Spring, Md.

FOR SALE - Following Tubes, factorysealed: 6SA7GT, 35Z5, 50L6, 12SK7,12SQ7, 5Y3, 25Z5, 80, 1N5, lAS, 1H5,and others. Two to a customer. No deal-ers. Also 15 new five -inch PM speakerswith output transformers to match. Mel-vin Okin, Suite 1103, 210 Fifth Ave.,New York, N. Y.

FOR SALE - Postcard camera, 1 electricshaver; 3 Brunswick 9 tube chassis, 1

RCA Victor R32 chassis and power pk.,1 fan, 1 Majestic 9013 chassis, 1 Majestic90 pwr. pk., several other chassis, andspeakers. All in playing order. Louis A.Goldstone, 1279 Sheridan Ave., Bronx56, New York.

Page 14 THE C -D CAPACITOR

TRADE-Rider's Manuals 1 to 12 inclusive,practically new, for a Johnson outboardmotor, 5 or 6 h.p., in very good condi-tion, or will sell for $100 cash. J. P.Miller, Ashland, Nebraska.

WANTED-Good used 3" oscillograph atreasonable price. Also any good 3 tube,3 or 4 band preselector (2 stage RFamp.) such as Howard 650, RME DB-20,or Meissner 9-1031, also RME LF-90 lowfrequency inverter. Michael j. Black-well, c/o Marine Hospital, Foot Califor-nia Ave., Memphis 5, Tennessee.

FOR SALE-Weston 0-1 dc milliammeter,model 301 like new. Four new RCA 954.Good used transmitting tubes, 2 RCA865, 2 RCA 828, 5 WE 212D with 2 WEtube sockets and Stancor filament trans.14v at 12 amps. Need 6 ft. Par -Metalrelay rack No. RR195 in A-1 condition.Joseph Mackora, 63 Pratt St., East Hart-ford, Conn.

FOR SALE -1 each Turner Hi -impedancedynamic mikes, CD, 22D, 33D, U9S Uni-versal; 3 2 -sec. floor type mike stands;3 -sec. floor type mike stands, 3 Utah12P PM, 12" spkrs., 2 crystal pick-upsAll new, mikes with 21 ft. mike cable.John J. Spankowitch, 239 N. 9th Street,Allentown, Pa.

WANTED -15 to 100W amplifiers, turn ta-bles, microphone stands, pickups andintercommunication units. Fox RadioService, 435 So. 5th St., Richmond, Ind.

TRADE --0-1 milliammeter, Rider Manuals,test equip., tubes, radio equip., etc.WANT K&E Engineer's slide rule orequal, LC checker, Jr. v-ohmist, oldwatches and jewelry Robert G. Brown-ing, 552 Eleventh Ave., Prospect Park,Pa

WANTED-Wireless phono oscillator, 1, 2or 3 tube,in working order.Also 35 mm.candid camera or 127 size for cash.Have sound picture supplies; projectors,lamp houses, generators, rectifiers,sound heads. john Arnold, P. O. Box 84Bluffs, Ill.

FOR SALE-Readrite tube tester model 430and Ranger Examiner Signal generatormodel 557 with new batteries. Any rea-sonable offer accepted. The ModernHome appliances, 4A Mechanic St.,Webster, Mass.

CASH WAITING - For your pickups orphono motor. Send description and priceto Joe's Radio, 2224 W. Belden Ave.,Chicago 47, Illinois.

WANTED-Receiver, such as HQ120, Ham-merlund, or AR77 RCA or equivalentRobert Rath, 4835 North Kostner, Chi-cago 30, Ill.

FOR SALE -1941 Philco auto radio almostnew, $35; 1937 Delco auto radio, goodcondition $20. Want Oct., Nov. 1937,and Nov., 1938, issues of Radio News.Paul Cespito, 637 W. 2.1 St., Erie, Pa.

WANTED-Will pay top cash for Supreme560-560A Vedolyzer and 561 audio oscil-lator. If you have phone include num-ber and price in your letter. Carl Vor-licek, 3621 E. 63 St., Cleveland, Ohio

WANTED-All kinds of radio test equip-ment, analyzers, etc. Quote what youhave to sell and lowest cost prices.National Sound Equipment Co., 625Main St., Worcester, Mass.

WANTED-FM receiver or converter, alsotelevision receiver and late communica-tions receiver. Will pay cash or trade lotof hard to get tubes and parts. CarlH. Stello, 925 Monroe St., N.E., Wash-ington, D. C.

MUST SELL NOW -1 Webster 4L35 35 w.amp., 2 30 w. booster amp., Hickockoutput meter, 2 Cinaudagraph HWAunits with SW horns, 1 University PAHunit with LH horn, 3 shielded 200 ohmto grid line trans., 2 model 55B ShureUnidyne, 1 RCA 50-A inductor mikeswith floor stands, 1 Brush B1 hand mike,1 250, 1 100, 1 75 and 2 25 ft. lengths 2wire shielded mike cable, all with Am -phenol connectors, 6 Oxford 12" dy-namics with horns, all like new. John'sRadio Shop, 32 Maple St., Perry, Ohio.

FOR SALE-One Unitron battery charger.Takes from 1 to 12 batteries at 15 amps.in A-1 condition. Price $50, cr will swapfor testing equipment such as multime-ters or any useful equipment. Lovett'sRadio Shop, P.O. Box 143, Newland,N. C.

FOR SALE OR TRADE - Automatic codemachine, 3 955 acorn tubes, auto vibra-tors and transformer, 7" Triplett founda-tion meter, photo electric cell, with re-lay, chassis, etc. What have you. Joe'sRadio, 2224 W. Belden Ave., Chicago 47,Illinois.

FOR SALE - Zenith deluxe trans -oceanClipper portable radio, model 7G605, likenew, extra battery. Also F 1.9 lens 50mmGundlach-Manhattan. Best cash offer orswap for communications receiver, orwhat have you? J. J. Cermak, 1928Grove, Berwyn, Ill.

FOR SALE-Back numbers of radio andmechanical mags., Radio Craft, RadioNews, Short Wave Craft, Popular Me-chanics, Popular Science, etc. AubreyEdgerton, 116 W. 6th Ave., Houston 7,Texas.

SEPTEMBER, 1944 Page 15

>1./«.,e4-

- writes W. B. GILLESPIE, Prop.Gillespie Radio Service

O'Neill, Nebraska

"I use C -D Condensers and have for severalyears," continues Mr. Gillespie. "Am stillwaiting for the first failure!" Hundreds ofthe nation's leading servicemen have usedvirtually the same words when writing us.Outstanding perfcrmance pays off -inadded profits, customer good -will and val-ued repeat business You can standardize onCornell-Dubilier Capacitors with confidence!

WRITE FOR CATALOG

MICA PAPER . ,D KKN[t,WE AND DRY ELECT/0[1'71C

CAPACITORS

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NAY/ETON BLiDSO. PLAINFIELQ,

N.USET

ODA y THAN ANY OTHER MAKE