KAD10 - World Radio History

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KAD10 -ELECTRONICS \KEFERENCE

ED, R. ALLAN

ANNUAL PHONE 41-0 - BOX 42RADIO SZ-_RVICE

PIC-TONI ONT.

111947

PUBLISHED BY:

RAD110-CRAFT

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25 WEST BROADWAY NEW YORK 7, N.Y.

halliErafters &mat& 5-New beauty and per-fect ventilation in theperforated steel top

Separate electricalbandspread with in -ergo flywheel tuning.

Tuning range from

540 kc to 42 Mc con-tinuous in four bands

Self-contained, shockmounted, permanentmagnet dynamicspeaker

All controls log,callygrouped for easiestoperation. Normalposition for broad-cast receptionmarked in red, mak-ing possible general Automatic noise 3 -position tone Standby receive Phone lackby whole family,Control switch

(APPROXIMATELY)

design, new utility in a great $ 50new communications receiver .. .Here is Hallicrafters new Model S-40. With this great communications receiver, handsomely designed,expertly engineered, Hallicrafters points the way to exciting new developments in amateur radio. Readthose specifications ... it's tailor-made for hams. Look at the sheer beauty of the S-40 ... nothing like itto be seen in the communications field. Listen to the amazing performance ... excels anything in its priceclass. See your local distributor about when you can get an S-40.

INSIDE STUFF: Beneath the sleek exterior of the S-40 is a beautifully en-gineered chassis. One stage of tuned radio frequency amplification, theS-40 uses a type 6SA7 tube as converter mixer for best signal to noiseratio. RF coils are of the permeability adjusted "micro -set" type identicalwith those used in the most expensive Hallicrafters receivers. The highfrequency oscillator is temperature compensated for maximum stability.

From every angle the S-40 is an ideal receiver for all high frequencyapplications.

halliErafters RADIOTHE HALLICRAFTERS CO., MANUFACTURERS OF RADIOAND ELECTRONIC EQUIPMENT, CHICAGO 16, U. S. A.Sole Hallicrafters Representatives in Canada: "nets Majestic Limited, Toronto - Montreal

COPYRIGHT 1946 THE HALLICRAFTERS

RADIO -ELECTRONICS

REFERENCE ANNUAL

CONTENTS

Theory and EngineeringNomogram Principles . by Fred Shunaman 25Laws of the Atoms by Helen M. Davis 31

Construction and Design3 -Tube Reflex Receiver by W. T. Connatser 4V.H.F. Transceiver . by L Queen 9

Amplifier and Radio Tuner by Cyril G. Brennan 14Radio Hearing Aid by Angelo Montani 15

Aids to Radio ServiceSensitive Signal Tracer by Clyde Zwieker 6Dynamic Handful Tracer by Ralph Bloom 16Radio Laboratory in Portable Unit by Wesley Neelands 19Radios Serviced by Observation by Lyle Treakle 20

Test InstrumentsA Multipurpose Tester by Bob White 12All -Band Oscillator by Bob White 17Pocket Radio Checker by Harold Pallatz 22Diode Crystal Probe , by Robert E. Ahomare 23

Sound AmplificationMaximum Fidelity by J. C. Hoadley 2A Vibrator Amplifier by John S. Straede 8Three -Channel Amplifier by M. Contassot 11

Charts, Tables and FormulaeOhm's Law in Graph Form 24Wattage from Ohms and Amperes 24Resistance of Wires 26Frequency from Capacity and Inductance 26A Decibel Nomogram 27Frequency -Wavelength Conversion 28Coil Design Nomogram 29Capacitor Markings 30Expanded Wire Table 32Reactance of Coils and Condensers 35Decibel Acoustic Scale 38Scale of Preferred Numbers 311Radio Unit Conversion Ratios 40Common Radio Abbreviations 46

Copyright 1946 by HUGO GERNSBACK 1947

MAXIMUMFIDELITY

NUMBER of years' experiencebuilding maximum -fidelity am-plifiers and sound systems have

led to the formulation of a set of rules,which, if followed, will enable the lis-tener to realize the best from any soundsystem.

First and foremost, the psychologicalfactor must be considered. People aredefinitely different in their tastes anddesires, and these desires change withthe type of program they are listeningto. Your amplifier should be equippedwith some means of varying its re-sponse curve, preferably with independ-ent treble and bass controls.

It is often stated (and rightly so, ifthe statement is qualified) that a flatamplifier is ideal. If we had a flat micro-phone, a flat amplifier and a flat speaker,located in a perfect acoustic chamber,and if the speaker output were exactlyas loud as the sound source, the systemwould indeed be ideal.

Even with this theoretically perfectsound system, if we turned the volumedown to one-half the loudness of thesound source, it would no longer soundlike the original, because we have intro-duced a new variable, our ears. The hu-man ear's response curve varies withloudness. The lower the volume the lessability there is to hear very low andvery high frequencies.

Room acoustics have a profound ef-fect on the ultimate sound of the sys-tem, and as there are few ideal roomsoutside of broadcasting stations or lab-oratories, this is another item to bereckoned with. In addition to thesethings, few pickups, speakers and mi-crophones are flat.

Now that we have an idea of whatwe have to contend with, let's get downto cases. Though the frequency re -

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Excellent re-production ofrecorded mu-sic depends onthree factors:compensationfor recordingcharacteris-tics, a goodamplifier, with special attention to theoutput transformer, and a speaker andbaffle system which turns the outputto sound with a minimum of distortion

sponse of a system is important, themost disturbing element in any systemis distortion. This will be more apparentat the higher frequencies, so limit thefrequency response of the system till itis just sufficient to reproduce the mate-rial on hand. There is no advantage inusing a system flat from 20 to 20.,000cycles to reproduce a shellac pressing.The high frequency noise and distortionwould be unbearable. Neither could weuse an inexpensive phono motor withthis wide -range system without therumble in the motor being very appar-ent. So-called permanent needles whenworn cause a particularly annoyingtype of distortion, in addition to caus-ing permanent damage to the records.

The response of an AM receiver neednot be any wider than 40 to 5000 cyclesfor the average station when broadcast-ing network programs, and 30 to 9500

cycles is entirely

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satisfactory for thebest AM stationswhen broadcastinglocal programs.Limiting the re-sponse to 9500 cy-cles is to suppressany 10-kc beats be-tween other sta-tions located 10 kcapart. For FM re-ception or tran-scription reproduc-

Photo A-Front view

of speaker cabinet.

Position and compari-

five sizes of vent

and speaker hole are

clearly shown here

tion we can go the limit and provideresponse from 30 to 15,000 cycles, foronly in these sources is the distortionlow enough or the range wide enoughto warrant this wide range.

In the reproduction of any record wemust take into account the various re-cording characteristics and compensatethe pickup accordingly. Standard shel-lac phonograph records are recordedwith a "modified" velocity character-istic. Amplitude of the cutting stylusis held constant from the lower fre-quency limit to between three and eighthundred cycles, and modified constant -velocity above this crossover frequencyprovides a five to ten decibel boost at8000 cycles. See Fig. 1.

This is done for the following rea-sons:

1. Due to widespread use of crystaltype pickups, the manufacturers of rec-ords insert a high frequency boost toreduce the compensation necessary toflatten the playback equipment's re-sponse. This boost effects a considerableimprovement in signal to noise ratio.

2. A large majority of the users ofshellac pressings have equipment withserious attenuation of the higher fre-quencies and no means for the com-pensation thereof. As the figure shows,there is a falling -off at the low fre-quency end of the audio spectrum. If thelaw frequency amplitude were not re-

stricted, either overcutting would re -

2 1947 RADIO -ELECTRONICS REFERENCE ANNUAL

suit or the level of the high frequencieswould be below the noise level.

Pickup CharacteristicsIf constant velocity records (without

treble boost) are ,played back with amagnetic pickup the output will be flatwith decreasing frequency down to thecrossover frequency where constant am-plitude begins. Since the magnetic pick-up requires successively greater stylusmotion at the low frequencies to main-tain its output flat, and since the am-plitude is held constant below the cross-over frequency (300 to 800 cycles)we must provide an equalizer to com-pensate for this condition. Since prac-tically all commercial records made inthe last six or seven years have a trebleboost, the magnetic pickup must befurther compensated to reduce its highfrequency response. Otherwise responsefrom commercial records will be ex-cessively brilliant. Fig. 2 shows theusual method of equalization. Constantsare approximate and depend on the pick-up and transformer, as well as the re-cording characteristic of the records be-ing played. Condenser C is for trebleattenuation. Its value may be anywherefrom .002 to .02 btf, depending on thepickup and transformer.

DYNAMIC PICKUP SOK

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Fig. 2-Two suggested equalization circuits.

A crystal pickup has a constant am-plitude characteristic. Its output voltageis a direct function of stylus motion in-dependent of frequency up to its high -frequency cutoff point. For constantvelocity recording (without trebleboost) above the crossover frequencywe would have to compensate for thedecrease in stylus amplitude with fre-quency. This is in the order of six dbper octave above the crossover fre-quency. To compensate the pickup forthis would require considerable boostat 7000 cycles. However, commercialrecords insert treble boost at a rate offrom two to about five db per octaveabove the crossover frequency, depend-ing on the record. Thus for some rec-ords no high -frequency equalization isrequired and for others only a smallamount. The customary method of com-pensating crystal pickups for commer-cial records is shown in Fig. 3. Reduc-

XTAL PICKUP 2MEG

500K

Fig. 3-Equalizer circuit for crystal pickup.

ing the value of C will reduce theamount of treble boost. For maximumboost C should be about .002 When

playing records having considerabletreble boost, C should be reduced invalue to as low as 50 if. Tran-scriptions are recorded with more in-volved response characteristics (gen-erally they have considerably moretreble boost than records) and the man-ufacturer of the pickup should be con-sulted for information on equalizers forOrthacoustic, NAB Standard, Colum-bia or other transcription character-istics.

The AmplifierNow that we have a suitable flat

source of music we wish to amplify itwith as low distortion as possible. Theeasiest way to do so is to build astraightforward amplifier using triodetubes throughout. We can choose be-tween 6A3, 6B4, 2A3, 45 for the outputstage. These tubes should be arrangedin push-pull, as the attendant cancella-tion of second harmonic distortion andsupply -voltage hum is worthwhile, andreduces the first filter section require-ments. Of course, beam tubes (6L6 -6V6) can be used with feedback.

The most important purchase in con-nection with this amplifier is a goodoutput transformer. It will make moredifference than any other component.An output transformer may have apower rating of ten watts. This is some-what deceptive as it is usually meas-ured at some middle frequency, usually400 or 1000 cycles. The same transform-er may only be capable of transferringfour watts at 30, and six watts at 12,-000 cycles. This is a serious drawbackparticularly when we wish to boost the

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Fig. 4-Three self-balancinq phase inverters.

Photo B-Inside view of baffle in Photo A.

high and low frequencies. High -qualityunits are relatively inexpensive in com-parison to the results they will produce.A high -quality output transformer fora 15 -watt 6B4 amplifier can be obtainedfor $15.00 or so.

An input transformer need not beused if class -A operation is desired, asa phase inverter is adequate. Fig. 4

shows several inverters which. are de-generative and consequently self -bal-ancing and of the low -distortion type.If class AR or AB2 operation to obtainmaximum power output is desired, aninput transformer is needed to keep theresistance in the grid circuits of thesetubes low in the case of a small amountof grid current being drawn.

Fixed bias is desirable as it allowsgreater power output with lower distor-tion. Fig. 5 shows a simple way to ob-tain same when your power transformerdoes not have a bias tap. A separatetransformer winding is required. The -rectifier may be a triode similar to thosein the amplifier.

If you use an input transformer it iswise, in the case of an inexpensive unit,and essential for a high quality unit,to shunt feed the primary from thedriver tube. This does not hold for push-pull drivers, as their d.c. plate currentbalances out in the output transformer.

Be sure to bypass all cathodes withlarge enough condensers to eliminate de-generation at low frequencies. It is wiseto decouple every stage, both in the in-terest of low hum level and to eliminatethe possibility of motor boating or un-wanted interstage coupling.

One should, of course, use as good aspeaker as possible and it should bebaffled efficiently.

A bass reflex baffle offers many ad-vantages, among which are improvedbass respoose, higher sensitivity andcleaner high -frequency response. Thedistortion at low frequencies may be

(Continued on page 48)

1947 RADIO -ELECTRONICS REFERENCE ANNUAL 3

Mr. Connatser's 3 -tube radio in its cabinet.

AFEW years ago, a superhetero-dyne radio had to consist of atleast seven tubes because mul-

tiple tubes had not been developed. Nowa truly excellent three -tube super ispracticable, and the cost is very low.

Those skilled in the art of buildingradios need nothing further than theschematic diagram which, so far aspracticable, is intended to be self-ex-planatory. However, for others whoaspire to build their own set, here aresome fundamentals on how best to goabout its construction.

First consider the coils. Assume youare building a broadcast set, 1700 kilo-cycles (kc) down to 540 kc, and thatthe intermediate frequency (i.f.) is 456kc. The network Cl, C3 and L1 mustbe such as will cover this band. Thecondenser C3 can be of the compressiontype; its purpose is to correct forlength of antenna. Thus, if the antennais very short, more capacity is requiredin C3. If the antenna is long, less isrequired.

The coil, L1, should be iron -core. Anyradio -frequency iron -core coil can bealtered to serve the purpose by com-pletely removing the primary and about10 turns of the secondary. Also, a smallradio -frequency powdered iron -corechoke can be reduced to the propervalue. You may make your own, ifyou have the iron core. Start out withvery little capacity in C3 and graduallyremove turns from L1 and close up onC3 until the full band is covered by Cl.

Coil L2 is the oscillator, consistingof a primary connected to prong 6 ofthe 6A8 tube, and a secondary con-nected through the 100.api condenserto prong 5. It is tuned by condenserC2 and C5 (padding condenser), to afrequency 456 kc higher than L1, or

3 -TUBE REFLEXOne of the tubes in this novelcircuit is the LI. amplifier,detector and audio amplifier

from 2156 kc down to 996 kc. Coil L2can best be a good -quality air corefactory job, designed for use in a setwith 456 kc intermediate frequency.The capacity of condenser C5 must bethat specified by the manufacturer ofcoil L2, usually 350 to 400 up,f. Thecorrect value is most important. If thepadder is not correct, the circuits willnot track.

Condensers C1 and C2 ate ganged,and can have a maximum capacityranging from 350 to 370 [lg. If sectionC2 is a cutaway designed especially for456 kc, no padding condenser C5 isrequired. In this case the end of thecoil shown attached to C5 is connecteddirectly to ground instead.

Neither L1 nor L2 need be shieldedif one is mounted above and one belowthe chassis.

The first i.f. transformer is a 456-kciron core factory job. It should be goodquality, and generally will be pre -tunedwhen purchased. This is important, aswill be explained later.

The coils L4 and L5 make up thesecond i.f. coupler. L4 has a center tapto which condenser C13 is attached. Inthe beginning we made up L4 from asmall radio frequency choke, and L5from the primary winding of a radiofrequency coil. Small compression typecondensers were used to tune the coils.Condenser C13 was attached to the topof L4 with this early coil. Later wepurchased replacement windings for a456-kc i.f. transformer, one of the coilscontaining the center tap. The mount-ing shaft is cut in half and the twocoils mounted at right angles and asfar apart as practicable, in a can 3 to3% inches high. Obviously they maybe mounted in separate cans.

In the first i.f. transformer the coils

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are inductively coupled. In the second,the coils are capacity coupled throughcondenser C13. Hence, when separatedit may be impossible to tune them downto 456 kc. Accordingly, a few turns ofsuitable wire may have to be added toeach of these replacement windings.

The iron -core audio choke, L6, re-quires an inductance sufficiently largeto block audio frequencies. It must havea low d.c. resistance -400 to 600 ohms.Its inductance can be anything from 10to 15 henries. If you have or can obtaina medium size core, a suitable choke canbe made up by winding on about 2200turns of No. 36 or No. 38 enamel wire.The windings should be placed insmooth even layers with thin waxpaper between layers.

The speaker can be of the PM type,from 3% to 6 inches, and the outputtransformer, L7, must match the im-pedance of the output tube and, inaddition, the voice coil of the speaker.A universal transformer of suitable de-sign may be used. A dynamic speakermay be used instead of the PM. In thiscase the field coil will be used to filterthe B supply, replacing resistor R10.

Now consider the tubes. The 6A8 isthe converter. The 7E7 serves four dis-tinct purposes: 1-It is the i.f. ampli-fier, and in that role we want it tobe the most efficient, hence the low d.c.resistance of L6 and the high screenvoltage on this tube. 2-It is the diodedetector (prong 3). 3-It provides thea.v.c. (prongs 3 and 4). 4-Finally, itis the first audio amplifier. The cathodesof these two tubes go directly toground. Negative bias for them is pro-vided in an efficient, inexpensive andnovel way. A negative voltage is devel-oped at the oscillator grid (prong 5)of the 6A8 tube, which is dropped toapproximate correct value by the re-sistors R1 and R3. Resistor R3 must beinstalled close to prong 5 and the otherend connected to the a.v.c. circuit. Addi-tional negative bias is provided by thea.v.c. as required.

At this time attention is called to Rl.It further reduces the negative bias tothe lowest point consistent with stabil-ity. This resistor should not be installeduntil the set is tuned and tried out.Start with 2 megs and vary.

The 32L7 tube serves the double pur-pose of audio output tube and B -supplyrectifier. Due to the excellent filteringthroughout the set, resistor R10 can be500 ohms, or less, at 2 watts. The values


shown for C16 and C17 are about mini-mum, but higher values may be used.

The tubes shown on the schematicmay be replaced by 12A8, 12SF7 and70L7-GT, with some advantage gained.In the first place, a current -limiting re-sistor of about 160 ohms, 10 watts, canbe mounted within the chassis, clear ofall parts subject to injury. Then too,the 70L7 is a better amplifier than the32L7. Note the different socket connec-tions for the 70L7, and that a differentsocket with different connections is re-quired for the 12SF7. This tube has butone diode plate; therefore, no connec-tion is made to a second diode. Allother parts, connections and values re-main the same.

The 6J7 type tube may be used in-stead of the 7E7 (the 12J7 type insteadof the 12SF7), the suppressor grid be-ing used as the diode plate. When thistype tube is used, the screen gridshould be connected to prong 4 of the6A8.

One of the unique features of thisset is the method of connecting thevolume control (R9) and the tone com-pensation circuit (R8 and C19). (Thevalue of R9 may be increased to onemeg.) Note also that the output tubeis brought within the a.v.c. circuit. Re-sistor R8 and condenser C19 are con-nected between the detector circuit andthe tone tap on R9. The value of R8can be 300,000 ohms; that of C19 200iinf. An increase in the resistanceor a decrease in the capacitance givesa brighter tone, and vice versa. This isthe most efficient method of tone ad-justment and noise suppression thatI've found. The value of condenser C20is not critical, and can be anythingfrom .01 to .05.

Harmful radio -frequency feedback,or regeneration, is prevented by thenetwork R7, C8, C11. The small amountof audio feedback passing through con-denser C13 is grounded out in L4.

The noise level of the set is extreme-ly low, due probably to the limitednumber of tubes and parts used.

To begin construction you will needa chassis, but this item-except thecabinet-is the last thing to procure

by purchase or home manufacture.When all the parts have been acquired,arrange the layout on a substitutechassis or breadboard so that all leadswill be as short and direct as possible,with all controls at the front panel.Grid and plate leads must be very shortfor best results. It's a good idea tokeep leads as close to the chassis aspracticable, since leads that stand outfrom some grounded metal object pro-vide greater opportunity for harmfulcoupling.

In your tentative layout, you mayfind that better wiring facilities can beobtained by changing one or more ofthe parts. Accordingly, juggle themaround for the best possible plan. Insome cases the position of a part maybe as important as its value.

A metal chassis may introduce effectsabsent in the breadboard hookup, dueto its shielding effect and also its ca-pacity to wires running close to it. Alayout that works well on the bread-board will usually work well on thechassis, as the latter has a stabilizingtendency.

Chassis size will be determined large-ly by the size of the speaker used andthe diameter of choke coil L6 whenthis coil is mounted underneath. Thesize of the cabinet will be determineuby size of speaker and chassis.

Fit the speaker to the chassis accord-ing to your plan, then lay it aside asthe last thing to be permanently in-stalled, to prevent possible injury tothe cone.

Always wire the filament circuit first,according to the diagram, then insertthe tubes and test by plugging in theline cord. If the tubes light, you willknow that the wiring is correct to thispoint. Now remove the tubes and pro-ceed with the remainder of the wiring.

Use rosin -core solder, the best youcan obtain, but do not use it excessively.

Assuming the i.f. transformer, L3, ispre-ttined when purchased, use it asthe beginning for tuning the other coils.Tune in a station near 1600 kc and ad-just L1 and L2 for best results. Nowadjust L4 and L5. Tune in a stationnear 600 kc to determine whether the

Right-Under-chassis view of the Super -Reflex radio, front -chassisview of which is shown below. The dial is a home -construction job.

set is tracking, for until you obtainaccurate tracking you have a poor radio.A single turn more or less on L1 canchange the tracking for better orworse. Now try adjusting the trimmerson L3 for better results, but first makecertain of the original position of theadjusting screws.

The antenna can be anything froma few inches to several feet. One of sixto.ten feet should be sufficient if thereare nearby stations.

Some means for checking the continu-ity of circuits and for shorts is almosta necessity. Even a flashlight batteryand a bulb, or a d.c. voltmeter can beused. An open circuit means failure; ashort can mean disaster. In general, aconstructor is well-advised not to workwithout at least a cheap multitester (orpreferably one of good quality). Tryingto build a set without one is almostlike trying to wire up the parts in thedark. Needless to say, a tube manualshould be part of the constructor's firstequipment, more necessary than hispliers.

With the exceptions noted, the valuesof the component parts for this set arenot too critical. Substitutions may bemade where necessary, but it should beremembered that the values specifiedare used in the original set. Variouschanges may be made to suit the con-structor's taste or the material at hand;the only necessary requirement beingordinary common sense.

With this set (in late October)speaker reception from ESL, over 600air miles, was constant around theclock; KOA, over 900 air miles, came inafter 3:30 P.M.; and other good clearchannel stations up to 3000 miles after6:00 P.M.

The cabinet, tuning dial and chassisshown in the photographs are all home-made. The cabinet, made from materialstaken from an apple crate, measures75/8 x 41/2 x 51/2 inches; the chassis, madefrom aluminum, measures 7 x 4 x 1%inches. The dial is made from a disk ofwood 3/16 -inch thick and 21/4 inches indiameter, two old volume control bear-ings, a piece of fishing line for a beltand a tension spring.


SENSITIVE. SIGNAL TRACER

BECAUSE of the distance frompowerful broadcast stations atthis location, many signal tracers

are not sensitive enough to give a posi-tive indication when applied to theantenna or first stage of a radio re-ceiver. This tracer was built with theidea of getting a stronger signal andhas given satisfactory service for twoyears.

Standard practice has been largelyfollowed. Switch 1 at the input tunesthat stage roughly to i.f. or r.f. It alsohas a position for antenna, providinga source of modulated signal whereneeded.

Practically all radios today have in-termediate frequencies falling between440 and 480 kc. The i.f. range was setfor these frequencies, no provision be-ing made for the few receivers whichuse 175 kc. Adjustable Meissner iron -core r.f. coils and 365-µµf tuning con-densers were used for the r.f. circuits,and by shunting these with small pad-ders it was possible to tune across theselected intermediate frequency bandvery nicely. A push-pull wave -changeswitch out of an old Victor radio wasused for this purpose. This unorthodoxmethod of adding an i.f. range is en-tirely satisfactory and very simple.

It is possible that if old-style 500-ppftuning condensers could be obtainedthe padders could be dispensed with,

An excellent instrument for radio servicemenin regions of low signal strength. Checksall circuits of a superheterodyne receiver.

although there has been absolutely notrouble with the present arrangement.

Construction DetailsTo get the required sensitivity, three

tuned stages were needed. Shieldingwas also necessary to prevent oscilla-tion, as were the 15,000 -ohm resistorsacross the first two primaries. If twotuned stages are used, there is no tend-ency to oscillate and there will beenough gain for most applications.

The oscillator section is simple andof standard design. The coils, switchand tuning condenser for it were sal-vaged from an old Philco radio. Theprimaries were removed from the coils.This section is the least used part ofthe instrument, but proves its worth inlocating intermittent troubles.

Probes for the r.f. and oscillator sec-tions are made from Belden microphonecable with tiny capacitors near thepoint of the prod. These capacitors aremade from two small strips of copperoverlapping each other a quarter of aninch and dressed down to go into theprobe. A number of other methods ofmaking r.f. probes have been describedin recent radio literature. The idea isthat the capacity should be very small.This prevents loading the circuits towhich the probe is touched, yet passesenough signal to operate the tracer. (Infact, signals can be picked up with theprobe held nearly an inch from r.f. or

i.f. leads of a properly -operating re-ceiver.) About 30 inches is fine forcable length.

The vacuum -tube voltmeter needs noexplanation. The cable for this part ofthe instrument has a 1-megohm resistornear the prod point. Sw6 selects thevoltage range. The 1000 -ohm controlused for the volts scale must have alinear taper. Its pointer is the centerone on the panel. The scale was madefrom Bristol board and calibrated byusing a power pack and voltmeter. Zerois in the center. The zero setting is madewith the 100 -ohm wire -wound variableresistor in series between ground andcenter -tap of the high -voltage winding(the most negative point in the circuit).

The Two Main RangesDial scales for the r.f.-i.f. and oscil-

lator condensers were also made ofwhite Bristol board. They were cali-brated with the help of a signal genera-tor and broadcast stations. The left-hand dial, which controls the r.f.-i.f.gang, has the padder switch mountedabove and slightly to the right. Whenit is in the out position, the instru-ment tunes over the broadcast band. Inthe in position, it tunes intermediatefrequencies. The padders can be seenmounted above the gang, in the rear-view photograph. The dials are of thelarge 2 1/16 -inch type with celluloid

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pointer. These look verywell, and the hair -linemakes accurate readingseasy.

The front panel wasmade from ,a -inch sheetaluminum. It is 12 incheshigh by 18 wide, with the5 -inch speaker mounted asshown in the photos. Thechassis is 10 x 17 x 3inches, which is about theright size to mount theparts. Standard phonejacks and plugs were usedon the ends of test cables.

The various controlsmay be seen from the pho-to. The four electron -raytubes are lined up alongthe top, the indicatorsreading from left to right:r.f.-i.f.; a.f.; v.t.v.m.; os-cillator; with the speakerin the center. The pilotlight is directly below withthe on -off and speakerswitch on either side of it.Farther down is the point-er and scale for thev.t.v.m., with its zero -set


adjustment on one side and its rangeswitch on the other side of it. The twopointers and scales at either side of thepanel are the r.f.-i.f. tuning, and the

R.F.-1.F DI

INPUT

SWI

ANT. J..0015 .015

6SK7

5 10K

-H-1.60K TK 1

DSC.

1r-HIPUT

0001

100

6AC7

751(

MA

MEG 6E5

equipment and methods will cover allpoints that might be raised in connec-tion with this piece of apparatus. Theinstrument is adapted to use as a multi-

SW5

6SK7

60K /K 60K

IMEG

VT.V.M.

INPUT UMEG

LI MEG SW

MEG

21010

9010

6Q7.0002

of misaligned i.f.'s, which can be dis-covered by tuning the i.f. channel ofthe tracer and noting the frequencyof greatest output. Realignment is sim-

tm

615

X ,2 MEG. 250K

25KIOW

1000

W.W.LINEAR

Complete schematic of the sensitive signal tracer. Resistor and con denser values at Switch

oscillator tuning scales. At the bottomof the panel, reading from left to right(in a staggered line) are the antennaswitch (Sw 1) the r.f. level control, theoutput switch (Sw 4) the audio volumecontrol, the audio input switch (Sw 3)the oscillator attenuator and the oscil-lator wave -change switch (Sw 2). Thejacks used with some of these switchesare placed as close to them as possible,to avoid long leads.

Functions of all switches, ray -tubes,dials and input and output jacks aregiven in the combination photo -sketchon the preceding page. The more impor-tant points may be marked directly onthe panel face, as was done in the caseof this instrument. For example, allthe ranges of the v.t.v.m. were printedon the panel. The antenna position ofSw 1 is marked with a large A. Thesame A (this time for Audio In-put) appears on Sw 3. It indicates thefull -volume position of the switch, whenthe volume control has no signal -reduc-ing shunt resistors in parallel with it.The tracer is commonly kept set to theindicated positions, which are the mostfrequently used.

Possibly the constructor should printthe names of every one of the variouscontrols, jacks and indicators on hispanel. The designer of an instrumentfeels so familar with it-even before itis built-that he seldom feels the needfor most of these indications, but aperson constructing it from the dia-gram would doubtless save time if hecould distinguish between all controlsand switch positions at a glance.

A study of the schematic will showhow the tracer may be used for dif-ferent purposes. A full explanation ofthe manner of emplOying it would takeanother article and is unnecessary.There is no difference in the operationof this and any comparable tracer, anda standard work on signal tracing

channel signal tracer. Clips may be at-tached to the cables and connected toseveral parts of a set at the same time.(Note that though the diagram showsstandard post -and -ground symbols,these are jacks in the actual instrument,and the ground is made to the shield ofthe probe cables.) The radio may be leftto play till it stops by itself. The eyewhich opens locates the defect.

Let me suggest that a broadcast sig-nal be used for tracing intermittents.They show up much quicker on a va-riable modulated signal of broadcaststrength than on a steady modulatedsignal from a signal generator.

An especially valuable feature of thetuned type of tracer is quick detection

1.0001

6V601

R.F.--0E

OWL

OUTPUT

Vt

OUTPUT

JACK

lois KIT icor

150

100

30 W.W. 75

,I0V-r"411VIZERO SET

6.30X

+300V

tf..-6H6

SW1

147 0 AL.

1

3 are explained in note at end of text.

ply a matter of setting the tracer's i.f.channel to the correct frequency andadjusting receiver i.f. trimmers to great-est output.

While this instrument is a bit morecomplicated to build and operate thanmany simpler ones described, the dif-ference in performance more thanmakes up for any extra trouble in build-ing and familiarizing oneself with it.

Note: The resistor and condenser val-ues in the audio input circuit (Sw 3)were inadvertently omitted from theschematic. The condenser is .01 Id(value not critical). The resistor inseries with the bias cell is 50,000 ohms,and the resistors shunting the volumecontrol are 2,000, 20,000 and 200,000ohms respectively.

A rear view of the sensitive signal tracer. Note trimmer condenserbank and switch mounted on top of the variable condenser gang.

1947 RADIO -ELECTRONICS REFERENCE ANNUAL

A VIBRATORAMPLIFIERA G -molt public address system,which can be transported easilyto out-of-the-way places and hasfair power and audio quality.

Handles permit transportation by two

people. The wafer sockets are input and output connections.

THIS amplifier is rather orthodoxin general design except thatvery special attention has been

paid to the two factors of efficiency andportability.

The author has a number of ampli-fiers, ' both a.c. and battery -operated,but had to confess himself beaten whena request came to rent out an extralight job to be used in a sports meet-ing on a loose sandy beach. As themeeting was three-quarters of a milefrom the nearest road or firm surfaceand as at least 5 or 6 watts were re-quired, there were problems. Have youever tried carrying a standard batteryoperated amplifier (and batteries) overhalf a mile of loose sand ? We decidedto build up a special job for futureoccasions.

To achieve light weight, a smallcompact motorcycle battery (6 volt 12ampere -hour rating) was decided on,thus permitting a maximum current

drain of about 4 amperes for 3 hours.The small power meant that overallefficiency had to be extremely high.One and a half amperes was allottedto the heaters, leaving 15 watts for theinput to the vibrator pack, the outputof the pack being 11 watts.

The Output CircuitThis output was sufficient for a pair

of 6V6GT's in class AB1 to providearound 6 watts of audio power. Actu-ally the drain on the pack was slightlyless under no -signal conditions. Thisreduction, together with the use of astandby switch, enables about 61/2 hoursto be obtained from each batterycharge.

The standby switch merely broke thecurrent to the vibrator -pack, therebyreducing the battery drain to 11/2 amps.

To keep battery drain to a minimumand yet retain reliability the tube line-up chosen was 6J7 -G as microphone

amplifier, 6Z7 -G asgeneral voltageamplifier and phaseinverter, two 6V6-GT's as outputtubes with semi -fixed bias and0Z4 -G as rectifier.A further 0.15 ampcould be saved byreplacing the 6J7 -G by a 6W7 -G. Byusing a separaterectifier with anon - synchronousvibrator, greaterreliability is ob-tained. Fortunately

.00025..

4-mIKEml

2501< 5 MEG

SW

-F. ®6V. A

6J7 -.003,400V250

\ .0 001

6Z7 2500

75K

RFC STAND-BY SZ156Th 0

40T NO18I/2.MA 5

- t

PHONOIt

4 - 0.75(5 0'01112V. 600V

EACH02

6V. NON SYNC. 240V/40MAVIBRATOR VI B. T PANS.

250 Kr( XI. .01 100K

44%

.0!-AATA02 50 K

6V6

20K

4KnCT.

EX.

I W

OZ4 T-.1

600 V7-7-14.501

Fig. I-Slight design modifications permit increased power output.

the OZ4-G has no filament to heat andits efficiency as a rectifier is good. A6SC7 twin triode can be used inplace of the 6Z7 -G with no change ofcircuit constants. Base connections aredifferent.

Phase Inverter DesignThe 6Z7 -G functions in a normal

manner as a paraphase type inverter,no by-pass condenser being requiredfor the cathode resistor. (There is nocathode by-pass condenser anywhere inthe design as grid -leak bias is used forthe first tube.)

It will be noticed in Fig. 1 that someof the circuit constants are unusual.There is a marked reduction in thesize of the coupling condensers so thatunnecessary parts of the audio spec-trum are eliminated. Bass suppressionis quite commonly used in public ad-dress amplifiers, the power thus savedbeing put into the more audible sectionaround the 1000 to 2000 cycle -per -secondband. A tone control cuts the "highs"when records are to be played or ifdesired, for "live" music.

Plenty of negative feedback is ap-plied around the output section, not toObtain a uniform frequency responsebut to reduce the distortion alwaysproduced when the output stage isoverloaded. Condensers across the pri-mary of the output transformer actwith the leakage inductance of thesame to cut off the uppermost of thehigh frequencies fairly sharply, there-by allowing a higher percentage ofharmonic distortion without producingtoo intolerable a sound.

Output TransformerAs only a limited frequency range

was to be handled, the output trans-former could be made small and com-pact yet high in efficiency. The lackof lower frequencies meant that lessinductance was required than usual,resulting in fewer turns, less ohmic re-sistance and less leakage inductance.A comparatively small core was used,the laminations being not interleavedbut butt -joined, leaving a very slightgap. Thicker wire than usual was em -



V. H. F. TRANSCEIVEThis "long -lines" transmitter -receiver corers boththe amateur band from 420 to 450 me and the pro-posed citizens' band, which includes 460 to 470 me.

WHEN activity started to boomon frequencies higher than 400mc, we decided to construct and

experiment with a compact, low -powertransceiver which would operate atthose frequencies. A portion of the 420 -to 450 -megacycle band (420-430 me)had just been opened, with the prospectthat the band would soon be extendedthrough to 450. Only a little above thatis the new citizens' band, from 460 to470 mc. This transceiver covers a rangeof 415 to 500 mc, including all theabove.

Not much thought had to be givento choice of tubes, as the field waspretty well limited to the well-knownand popular 955 acorn type. The smallsize fits well with the compactness ofother components at ultra high fre-quencies and the low power require-ments make it possible to run it ef-ficiently from the a.c. line or frommedium-sized batteries.

The complete set, except for speak-er or mike and power supply, can bebuilt in a space less than 4 x 4 x 4inches. This is the size of our unit butthe photograph shows unused spacewithin this volume. It is possible, forexample, to incorporate a small 2 -inchPM speaker or small "B" batteries forthe plates.

We were more interested in gettinga solid, clear signal out of the antennaand this has been accomplished. Vibra-tion and movement of the transceiverduring transmission has no adverseeffect on the signal and the frequencyonce set remains constant. There is noevidence of hand capacity during tun-ing. This instrument is definitely nota toy and the design has not beenlimited for the sake of compactness.

Experiments carried on over shortdistances within the same block showthat the waves pass readily throughpartitions and brick walls. Communica-tion over short distances did not re-quire the receiver to be equipped withantenna. Our experiments show thatwith no benefit of location a mile or socan be covered. Given the advantage ofheight the signals should go the line -of -sight limit with a reasonably goodsignal.

R.F. SectionThe circuit is a parallel -line affair

but with condenser tuning for conven-ience and ease of calibration. The linesare 1/4 -inch copper tubing, each 2 incheslong and separated by about % inch.The miniature 50 -aid condenser is con-nected across the far ends of the lines.The ends of the tubing connect directlyto the tube contacts.

Polystyrene blocks are used to insu-late and support the r.f. components.The presence of this material has noappreciable effect on the r.f. fields, andthough expensive, it is well worth-while. Leads between the r.f. and audiocircuits go through holes drilled throughthe polystyrene. The material machinesvery well, taking saw, drill or tapvery nicely.

The plate, grid and cathode circuitsmust be well isolated from other cir-cuits by suitable r.f. chokes. We wiredup a number of these experimentally,taking off turns until we arrived at anoptimum in each case. Quite a bit ofpower can be lost through inefficient orinsufficient chokes.

The tuned circuit is set back about1% inches from the front panel. Thiseffectively eliminates capacitance ef-fects, which we feared at first. Themetal shaft of the variable tuning con-denser is extended by means of an in-sulated coupling and a short length ofpolystyrene rod. The front panel willaccommodate a 2 -inch dial but we wereunable to locate one in Radio Row and

Top - The oscillator

circuit. Heavy tubes

are "long lines" and

bent wire is antenna

coupling. Below-Au-

dio section. Batteries

strapped to the trans-

former excite the car-

bon microphone.

The transceiver with power pack ( in rtarl

had to be content to make a home-made job. This was done by pasting acircular piece of paper with inked di-visions on the panel and using a smallbakelite arrow knob.

Power Output vs. FrequencyAs might be expected, the output is

appreciably greater at the lower fre-quencies. Even the acorn tube beginsto feel the effects of the u.h.f. Thesecan be shown by the following table:

PLATE LOW FREQ HIGH FREQ

VOLTAGE Ip 1g Ip lig

100V .25 ma 490 aA 2.5ma 11011A

220V 1.5 .. 850 . 4.0 - 250 -

These unloaded circuit values show thehigher efficiency obtained at the lowerend of the range.

The antenna consists of a 1/4 -inchaluminum tube about 5 inches long


within which a 3/16 -inch piece of tub-ing slides. This means that the total

955

I7TI/8"

.00005

15TVS"

ANTENNA

2

4111

3V B+Fig. I-Schematic diagram of the 420-450 megacycle transceiver.

IK

unit, but its costeliminated time a

SPR TRANS

955OR PHONES

LOT

1/8"

length can be extended to almost 10inches. A quarter wave -length is about61/4 inches at 425 me but the antennashould be experimented with for bestresults at any frequency. Coupling isprpvided by a half -turn of No. 16 wire.If a relatively great distance is to becovered it is recommended that anotherquarter wave -length be added on theother side of the loop, making a di-pole. Better yet, an array of directionalradiators should greatly increase therange in any given direction, but onthe other hand, will take the trans-ceiver a little out of the portable andconvenient -to -handle category.

A phone tip at one end of the anten-na (held by means of a screw throughthe tubing) fits into a tip jack andmakes the radiator removable whenthe transceiver is not in use.

Audio SectionThe choice of modulator (and audio

amplifier) also fell upon the 955 tube,but for different reasons. Here we wereconcerned with size and power require-ments, as well as the fact that twotubes of the same type make for sim-ple testing of tubes and permit put-ting the best one in the oscillatorsection. These tubes are not generallytested at the time of purchase and wecan only hope for the best. It happenedin this case that one was slightly

II7Z6

10 H

Fig. 2-The variable-vo tage power supply.

better than the other as an oscillatoron the high frequencies. There is noapparent difference in efficiency in theaudio stage.

Microphone CircuitThe circuit is conventional among

transceivers. We used a Stancor A-4413microphone and audio transformer.This is the largest component in the'

is reasonable and itnd effort that would

be spent in add-ing windings to astraight audiotransformer, as issometimes done.Since the purchasedunit matches a 200 -ohm microphoneand a 10,000 -ohmplate to a singlegrid input the am -plifier gives verygood results. Theoutput is ample torun a 2- or 3 -inchPM speaker and

with phones the signals are reallyloud! The primary of the speakertransformer (or headphones) acts asthe modulation choke.A carbon mike with two pen -light

cells is found 'to give sufficient modula-tion. There is plenty of room to addanother should the output of any partic-ular mike be found to be low, but 3volts is ample here. The mike jack isdesigned to short out the microphon'winding when the unit is used as a re-ceiver with no mike plugged in. Other-wise there is a terrific hum due to theopen winding. Plugging in puts thebattery in series with the winding. Ifthe mike has a "press -to -talk" switchit (the mike) need not be removed evenwhen a long period of transmission isscheduled. The circuit appears in Fig.1.

We don't find it necessary to includeanother switch in the speaker sec-ondary to avoid feedback to the mike.If the two are separated by a few feetand if they don't face each other thiswill not cause trouble. If necessary,however, the switch may be placedright on the speaker and need only bea single -pole single -throw type.

Power SupplyIt was found desirable to design a

small power supply which would de-liver sufficient voltage to run the trans-ceiver during the tests. The size ofpower transformer we would have likedto use and those available didn't coin-cide, so we went over to the voltage -doubler a.c.-operated idea. A 1117Z6-GTtube is used in the supply, which is il-lustrated in Fig. a

Relatively small condensers are usedacross the tube elements and a large(capacitance) value across the d.c. out-put. This eliminates some of the dis-advantages of high capacitance inputpower supplies (such as poor regula-tion, severe load on tube, etc.). A smallchoke was included to help smooth rip-ple. (See Fig. 2.). Hum is inaudible onthe speaker. Using headphones thereis a slight hum, as might be expected,but when the transceiver is oscillatingor super -regenerating it is very lowand is lost in the "rush."

The output of the supply can bevaried from zero (useful when making

tests within the set or changing tubes,etc.) to a full 225 volts at maximumdrain of 13 ma. A voltage control isalways desirable in connection withsuper -regenerating receivers and is agood thing when testing the transmitterat different inputs. It will be notedthat the voltage must be progressivelyincreased for satisfactory results asthe 500 me point is approached, other-wise the super -regeneration drops out,leaving only ordinary oscillation and avery insensitive condition.

The operation of super -regenerativereceivers and of Lecher wire frequen-cy checks has been covered in theliterature. The same principles applyto these higher frequencies. The fre-quency calibration of receiver andtransmitter must be made to a closertolerance as far as actual dimensionsare concerned. In other words, a frac-tion of an inch difference means morefrequency deviation above 400 me thanit does below 150. It will be found thatthe Lecher measurement will show asharper indication than at lower fre-quencies. The coupling should be ad-justed so that the same reading willbe obtained after several tries, within

inch or better. Even this shortinterval represents about 1% of thefrequency. The hand must not be kepttoo near the wires during the measure-ment. (Fig. 3, which appears below, isthe calibration curve.)

The 420 -me amateur hand offers anexcellent chance to experiment withreflectors, polarization, etc. Thus, asheet of aluminum placed behind anantenna will progressively and alter-nately increase and decrease the signalas it is moved steadily away from (or

FREQUENCY

520

500

480

460

440

420

4000 5 10 15 20

DIALFig. 3Calibration curve of the transceiver.

toward) it. Another rod or piece oftubing will act in the same manner.The latter may be held at its centerby the hand as it is moved toward andaway from the radiator. The effects ofpolarization are clearly shown in thisway.


THREE - CHANNEL AMPLIFIERIt has separate controls

WE must never lose sight of thefact, in considering the con-struction of any sound appara-

tus, such as an amplifier of frequenciesin the musical range, that it is the earwhich judges the excellence of the in-strument-absolutely without appeal!It is therefore indispensable to examinethe conditions under which that organfunctions, to adapt our sound equip-ment to it in the best possible manner.

The sensitivity of the ear varies asa function both of the frequency andintensity of the sound. If we considervery weak intensities, the ear hearsmedium -register sounds much betterthan basses or high -frequency notes.At medium intensities, all the frequen-cies are heard equally well, and forvery loud sounds, the basses and highsare perceived with greatest intensity.

The Curve of an AmplifierIt appears from the considerations

above that giving an amplifier a linearfrequency curve is completely illogical.It is necessary to so design the equip-ment that the listener will hear thesounds reproduced under conditionswhich approach as close as possiblethose of listening directly to the soundsource itself.

Let us take, for example, the case ofa symphonic orchestra. If the listeneris in his orchestra seat in the auditor-ium where the orchestra plays, he hearsthe music at such an intensity that hisear perceives it with the same relativesensitivity over the whole range ofmusical frequencies. But if he hears thesame program over his radio or fromrecords, through a loudspeaker in hisown living -room or bedroom, it isobvious that that intensity will not beas great-the size of a private roombeing considerably smaller than thatof a concert hall. If he turns up thevolume control to get the same soundlevel (which is possible) neighbors withdifferent musical tastes-or those whodesire the sleep of the just-will notbe slow in protesting energetically. Hewill therefore regulate the volume toa sound level rather on the weak side.

It is then that the ear registers itsdiscontent with this "sound rationing"by refusing to hear the low and highnotes with the same force as the fre-quencies in the middle of the audiblespectrum. But, if our critical listeneris clever and especially if he constructshis own amplifier, he will design itwith such a response curve that it over -amplifies the highs and the bassesrelative to the medium frequencies,to exactly the same extent as the eartends to weaken them. He thus doeshis own ears a good turn, at the same


for the treble, medium anti bass notes.

6A5

SY 3 BASSBIAS CONTROLS VOLUME MEDIUM

ON -OFFS ITCH PLATE CURRENT METER SWITCH 1-1!GN

IMEG

.00111

6F5R2 .00025

IMEG C2

INPUT

MEDIUM

.000025

6F5 6C5500K

R2I MEG

3K 10K

6J7R

500 .01

50K 22K 50K 250K200K P

.00005

6A5- C4

500n 500.n.

-/-60-.(Yr+10Mri÷1!6

P/,P2.P3ARE IMEG.P4 IS 500K.P5, P6 ARE 5K, WIRE WOUND.T I = COUPLING TRANS.T2=UNIVERSAL OUTPUT TRANS.K

SW

117 VAC

5V4TO 6A.5 F1LS ONLY

NOT USED5Y3

6V, . A

T2

2BASS &

M EDIUM3 SPKR

5 PHONES

R4 6IMEGC4.00005

260n, 130MA, 2511

+325 V

5KT

-.L.so 25200V T

P5

25 -7K

Many original features are to be found in this French high-fidelity, fixed -bias amplifier.

1947 RADIO -ELECTRONICS REFERENCE ANNITAI, 11

A MULTIPURPOSE TESTER

THE experimenter will find thisseven -tube test unit very useful.It incorporates a four -watt audio

amplifier with a built-in dynamicspeaker; an r.f. test probe; a twin in-dicator electron -ray tube with its sepa-rate amplifier; and a power supply. Thetester will trace a signal from aerial tospeaker of a receiver, and give a com-parative check of signal intensity. Itwill measure voltage, current, resist-ance, and capacity; and also test con-densers for open and short circuits.

The test unit was built in a venti-lated metal cabinet measuring 12 x 71/2x 7 inches. The chassis was made froma /-inch sheet of alloy aluminum meas-uring 11 x 61/2 inches. Since the heavyaluminum cannot be bent easily, it wassupported and fastened by means ofangle irons.

It is essential that extreme care betaken in wiring and constructing thetester. The leads should be well insu-lated. The jacks that are not groundedto the chassis can be thoroughly in-sulated by fastening them with live -rubber grommets mounted in the panel.

Toggle switch Swl permits the audioamplifier to operate either the speakeror a pair of phones connected to jacksJ10 and J11. R3 serves as a volumecontrol and also operates the powersupply switch. The grid cap lead fromthe 6J7 tube should be shielded to pre-vent pick-up of stray noise and hum.

The socket of the 6B8 tube is fas-

This meterless instrument measures voltage,current, resistance and capacity, and is asignal tracer and 4 -watt amplifier as well.

tened to a three-foot six -wire shieldedcable. The tube must be shielded if the6B8 -G glass type is employed. ResistorR12 and condenser C15 are mounted onthe probe assembly, but all other partsare located within the cabinet. SwitchSw2 turns on the probe.

The 6AF6-G twin indicator tube hasboth ray -control electrodes tied to-gether so that two similar shadows areproduced. The tube was mounted on abracket with pins 3 and 7 in a verticalplane. Switch Sw3 turns on the targetvoltage. The 6K7 tube - connected asa triode amplifier-has two variablebias controls. The 1-megohm unit(R15), which has no dial or calibration,serves to set the shadow angle beforemaking measurements. R16, the750,000 -ohm control, is connected to afour -inch 325° calibrated CA precisionvernier dial. The latter unit is used formeasurements. The calibrated knob wasmounted on top of the cabinet, becausein this way the dial reading is not aptto influence the setting of the "eye."

The 6116 tube rectifies alternatingvoltages that are impressed on theelectron -ray indicator circuit, so thatthe image will be clear and sharp.Selector switch Sw4 connects the vari-ous testing circuits. When the indicatorcircuit is used in conjunction with thesignal tracing amplifier, potentiometerR18 regulates the intensity of the sig-nal affecting the indicator.

The power supply employs a 5Z4 tube

in a conventional full -wave rectifiercircuit. By using jacks J8 and J9 the"B" supply can be used to operate ortest external circuits, if the currentrequirement is not too large. The neonlamp serves as a safety "B" indicator.If the lamp should go out or glowdimly, the power supply should beturned off because this would probablyindicate a short circuit or a dangerouslyheavy load. If the "B" supply is beingused to supply power to a circuit to betested, the r.f. probe and audio testprod can be used; but it is impracticalto use any of the other tests simultan-eously.

Operation of the TracerSignal tracing is a very convenient

system for locating a defective stagein a receiver or amplifier. For tracingaudio -frequency signals, connect ashielded test prod and lead to jack J7.The signal may then be traced fromthe sound source to the output bytouching the prod to successive stagecircuits. The r.f. test probe is used forfollowing the signal from the aerialto the detector of a receiver. To operate,turn on switch Sw2, and connect ajumper wire from jack J7 to J6. Thesignal can then be observed or heardby touching the probe of the tube tothe r.f. and i.f. stages. Always connecta lead from J8 to the chassis of thereceiver whenever the signal tracer isused.

Top and bottom views of the instrument, front view of which appears

on next page. All measurements are made with the single dial


The volume control, R3, should beturned up about halfway for the aver-age signal. The electron -ray indicatortube can be used to observe the inten-sity of the signal. The tube is turnedon by switch Sw3, and connected to theamplifier by turning selector switchSw4 to position 1. Turn up the inten-sity control R18 until the indicator tuberesponds to a signal impressed on theamplifier. Set the uncalibrated bias con-trol R15 so that all of the resistance iscut out. This causes the "eye" to open.

The intensity of two or more signalsmay be accurately compared or matchedwith the indicator tube. With no signalpresent, turn the calibrated dial whichoperates R16 to 0 degrees (all resist-ance effective), and adjust the uncali-brated potentiometer R15 until theshadow angle is 0 degrees or the "eye"just barely closed. Turn the intensitycontrol R18 to its maximum setting anddo not change the setting during tests.Apply the signal to the unit and notethat the green image will overlap.Turn the top calibrated dial R16 untilthe indicator tube appears just as itdid with no signal present. Read thenumber of degrees indicated by the dialand then repeat the process for othersignals. If the reading is less foranother signal, the strength is less; ifthe reading is greater, the signalstrength is greater.

To connect the test unit as a volt-meter, turn on the power supply andindicator circuit with the switchmounted on R3, and toggle switch Sw3.Revolve the top calibrated dial (R16)to 0 degrees, and with R15, the uncali-brated control, adjust one section ofthe twin indicator tube until the "eye"just barely closes. Plug in the testleads to the red jack J1 and the blackjack J2. For measuring d.c. voltagesconnect the lead from J1 to the positiveside of the potential to be measuredand the lead from J2 to the negativeside. Turn the selector switch Sw4 toposition 2. If the voltage is not greatenough to cause the green image tooverlap, switch to position 3, 4, or 5.After the proper range has been sel-ected, rotate the top calibrated dial(R16) until the "eye" opens to the"just barely closed" position. Read thenumber of degrees indicated and referto the proper voltage chart.

Two of these voltage charts shouldbe made for each of the four ranges.One set is for a.c. and the other ford.c. voltages. These charts can easilybe prepared by applying known volt-ages and recording the number ofdegrees deviation from zero requiredfor each voltage. An accurate voltmeterused in conjunction with a variable a.c.and a variable d.c. source can satisfac-torily be used to calibrate the tester.

If it is not known whether the volt-age is a.c. or d.c., it can be determinedby reversing the leads. If the voltageis d.c., the 6AF6-G tube will indicatethe voltage only with the positive sideconnected to J1. If the voltage is a.c.,the tube will indicate the potential dur-ing both trials.

J I 6H6Ored

J3

black

_L

R19

R20

J2 R210

black

7RLt)23

C19 8R24

9

10

R25

NC

2

CI 7

R18 CI8±-AAKAI-)

6J7

6K7

W4

(5d7red

red

6B8--- 7"'Nyellowuel

black --1-40100% -

rdI

green- % Re, R

brown- i 7, `

, red c51

.--. --- I;--- '7C/Tei- J50 T4--1 RI It.jC14 red

- J4 04

rerfpii-FUSEIAMP

C15 R12R.F. TEST PROBE

THE SPEAKER SHOWN IS A 5" DYNAMIC

0

6AF6G JII

black

PHONES

CIO red

JI0vswi

771it.r: JSal

450.n.FIELD

+06-.`FILS CI C2T6.3V

SW ON R3

13+J9

117V AC

The instrument has more tubes than is usual for such a device. The 6B8 -G, is in the probe.

Position 5 will measure 1 to 32 voltsvolts a.c. or .5 to 41 volts d.c.; position4, 20 to 400 volts a.c. or 5 to 200 voltsd.c.; position 3, 100 to 1100 volts a.c. or50 to 600 volts d.c., and position 2, 400to 2500 volts a.c. or 200 to 1500 voltsd.c. Position 2 has a much higher theo-retical range, but due to arcing orbreaking down of the insulation in theselector switch or at the jacks, it isnot advisable to apply higher voltages.

One of the leads is connected directlyto the chassis; so, take care that themetal cabinet is on an insulated surfacewell away from the receiver or voltagesource and that the operator does nottouch the cabinet. It might be worth-while to insulate the cabinet from thenegative side of the "B" supply andto connect a small condenser from thenegative side to the chassis.

The test unit can be used for approxi-mate current -measurements in caseswhere the relatively high voltage dropwill not upset the operation of the cir-cuits. To set the tester for this func-tion, the following steps should betaken. Turn an the power supply andindicator circuit, revolve the top cali-brated dial to 0 degrees, and with theuncalibrated knob set the indicator tubeso that the green area of one sectionjust barely touches. Turn selectorswitch Sw4 to position 7, and plug inthe test leads to J1 and J3. Connectthe prods in series with the circuit tobe analyzed. For d.c. measurementsmake sure to connect the black leadfrom J2 so that as the electrons flowfrom negative to positive, they willenter that lead. Turn the selector switch


Front view of the instrument, showing controls. Designations refer to the schematic diagram.


HI-FI AMPLIFIERAND RADIO TUNER

Public address system plus a highfidelity superheterodyne receiver

THIS amplifier, an experimenter'sconsolidation of circuits, has satis-factory tone, volume and a num-

ber of useful auxiliary features. Theoriginal model is constructed in a 10 x 8x 10 -inch sloping front, metal cabinet,and on a 9 x 2 x 7 -inch chassis; anexternal speaker is used. Since wiringand components are close, all couplingcondensers, a.f. leads, and other sensi-tive components were shielded thor-oughly wherever possible. Output isabout 20 watts.

The circuit consists of: a superhetero-dyne tuner, a volume compressor -expander, a three -channel input withmixers (plus tuner input channel) anda high gain push-pull amplifier.

A double triode 7F7 is used for atwo -channel mike input, the grid leaksof each section forming volume con-trols for the microphones, thus servingas efficient mixers. The plates of the7F7 are coupled together through aone-megohm resistor, reducing ampli-fication but preventing any motorboat-ing. From here, the a.f. signal travelsthrough a switch on the back of oneof the mike controls, through a coup-ling condenser to the center -tap of the

p ,01

.5MEG01.

-.5MEG0-1

M2.01

7F7

7A8Li

.05T.

50.000

(,

7A7

Oa 3000

.03

7.0001

.0004.2 eAI a a

phono volume control, the lower sideof which is shunted with 50,000 ohms toground.

Compressor -ExpanderThe higher potential side of the

phono control, from whence the signalconies, is fed through a coupling con-denser to the grid of 7A7, used in avolume expander -compressor circuit,with little amplification value. Also, thesignal from the phono control is fedto the grid of a 7C7, which acts as anamplifier in the volume "expand -com-press" circuit.

From the plate of the 7C7, the signalpasses to one cathode (coupled to theopposite plate) of a double -diode recti-fier 7A6 (or 6H6). A center -tappedpotentiometer is coupled between theother cathode and the opposite plateto it, with the center -tap grounded. (Seefigure). As the signal amplitude in-creases, so does the potential in the7A6. The plate end of the expand -compress control will gain negativepotential, while the cathode side willbe positive, with respect to ground. Bymoving the control arm to the right orleft of center, variable degrees of posi-

sum

.2.05 == 50,000

7C7.1 MEG

25,000

.02

.25 MEG

7C6

5MEG

A tuner, amplifier and turntable in one unit.

tive or negative rectified voltage willbe applied as bias to the 7A7; this recti-fied voltage increases with signal ampli-tude, giving desired compressed orexpanded signal from the 7A7 plate.Expansion of volume is used to increasethe dynamic volume range of phono-graph records which were compressedduring the process of recording. Con-versely, compression of volume is some-times desired when using the amplifierfor recording purposes.

Leaving the 7A7, the signal is am-plified by a pentode -amplifier 7C7, thenby a triode 7A4. Here an audio trans-former is used as coupling to a pairof beam -power 6V6's or 6L6's, in push-pull. Inverse feedback is applied by a5-megohm resistor in series with ablocking condenser between the gridand plate of each 6L6. Since B -plusleads were long, an 8-microfarad con-denser was placed directly at the 6L6screen grids.

(Continued 012 page 40)

7A4

.01 I 6L6INPUT3:1

a

150 MA 5Y3

18 81,

6600.,

50011oc

;fc,

a.

`COMMONGROUND

300-0-300rw

-40

'81

6.3v. To ALL FILAMENTS

PHoNo MOTORII7v.AC

OFF o

_...L_TRIPLE POLE TRIPLE THROW

POWER SWITCH

PILOT

117V. AC

NOTE: I -F = 456 KC t L ANTE 1.2.0SC.

The Superamp 'comprises a high-fidelity amplifier and

14

a superheterodyne tuner. There is a radio, phonograph and two microphone inputs.


Left-Side view of the radio receiver hearing aid, showing length.Right-The whole instrument may be held in the palm of one hand.

RADIO HEARING AID

THE vacuum -tube hearing aid is es-sentially an audio -frequency am-plifier where a compromise has

been reached between performance,physical size and weight of the com-ponent parts. Frequency distortion ispurposely introduced to compensate forthe uneven pitch sensitivity of the earof the wearer. This compensation alsotakes into consideration whether theacoustic conduction is through air orthrough bone.

Commercial hearing aids use two -stage, or more generally three -stageamplifiers. This gave us the idea ofutilizing the same tubes and componentparts for radio reception. After someexperiment, the circuit shown at thebottom of the page was adopted, andgives good results in both capacities.

Throwing a switch transforms the setfrom a hearing aid to a radio receiverembodying the audio -frequency char-acteristics of the hearing aid. A thirdswitch position where the instrumentperforms simultaneously as hearing aidand radio -receiver is also mandatory.The wearer can then hear conversationwhile listening to the radio.

05

.00005

.00016 I7

Pr00005

OFF 11 2 3o o oSW

.05

This compact little nnit becomes, byswitching, either a radio receiver orhearing aid, or both at the same time

The fact that a hard -of -hearing per-son can enjoy broadcasts while sittingat his desk or walking in the streetmay have a moral and also a socialvalue. We hope that some technicalreader may benefit from it for his per-sonal use.

For the best performance, the circuithas to be individually "fitted" so faras audio -frequency is concerned; damp-ing that portion of the range where thedefective ear is most sensitive.

The superheterodyne circuit hasbeen chosen, incorporating necessarymodifications to amplify simultaneouslyat i.f. and a.f. "Slug" or permeabilityinstead of variable condenser tuningmay be preferred because of compact-ness and reduction of weight. Our ap-paratus is not exceptionally compact orlightweight because it was assembledwith parts available on the radio mar-ket at the time. To reduce the dimen-sions every component part should beredesigned.

The body of the wearer acts as acapacity -coupled antenna. A loop ofwire stretched inside the belt of thecarrying case forms one element of theinput condenser.

1S5

2 MEG

XTAL MIKE

ADJUSTABLE OSC. COILThe circuit is not complex, though reflexing and mixing of

IF OUTPUT

.00I

.0001

3 MEG

1R5

Several constructional difficultieswere encountered with the wiring. Feed-back from the audio -frequency gridleads is the most troublesome. The a.v.c.is also a source of trouble and-al-though represented in the schematicfor sake of completeness-was elimi-nated in the model shown in the photos.The a.v.c. voltage may be applied to theconverter only, since the 155 amplifiesboth at if. and a.f. Besides the 1S5 isnot a variable -mu tube.

The positions of the switch are: Off;1 - Hearing -aid; 2 - Radio -Hearing -Aid; 3-Radio.. Since we were unableto procure a very tiny switch we de-pended on plug-in contacts.

To easily visualize the operation ofthe tube 1S5 and its relative input andoutput circuits, we may refer to theconventional reflex amplifier. In a reflexamplifier the tube amplifies at r.f. ori.f. and at a.f. The a.f results from thedemodulation of the r.f. or i.f. In thepresent case the a.f. is generated by themicrophone.

The important switch decks are theones located between the first 1R5 andthe 185. When they are im position 1,

(Contii,ned on page 38)

I MEGI '0011S4

XTAL EARPHONE

I.02

-1.5V -45V

8+7 5 Ov

OF I+45 V0_i; I 2 3

svPtwo channels in the second


I R5 add a few puzzling touches to the schematic.

15

DYNAMIC HANDFULA signal tracer so compact that it can beapplied direct to the circuit being tested

THE unit to be described is intend-ed for radio servicemen who aretoo busy to construct an elaborate

signal tracer or audio amplifier.This tracer was designed primarily

to do away with power transformers,external test probes, specially con-structed test prods, coils, tuning con-densers, tap switches, externalamplifiers, high cost of construction,and to save valuable space on the ser-vice bench.

There are no special parts to beobtained and it takes very little timeto build the tracer. It is so small thatit can be placed inside your toolboxtogether with your other tools.

The volume of the signal tracer isadequate even when connected only toan antenna circuit. Very little hum isnoticed when operating it. The openspace on the front panel of the tracerlets the heat of the tubes out, indicateswhen tracer is on by the tubes lightingup, eliminating a pilot light, also pro-vides a space for the line cord if youintend to carry it with you on servicecalls.

The tracer was assembled on an a.c.-d.c. very small midget radio chassiswhich was cut in half, leaving the fourtube sockets and speaker alreadymounted, besides the wiring of theoutput tube and rectifier, which wasleft intact (because it is usually s,and-ard on all midget receive,. s), therebysaving quite a bit of the work involvedby not having to cut tube socket holes,speaker cutout and considerable wiring.There are several well-known makesof midget radios from which the chassiscan be cut to leave four tube socketsand a speaker cutout remaining. If asmall set cannot be obtained, a chassis

layout is illustrated so that the service-man can cut the chassis himself.

Any Tube ComplementThe serviceman can have his choice

of tubes to be used in the tracer. I usea 12Q7, a 12SQ7, a 50L6, and a 35Z5tube. These were the tubes I had onhand at the time of construction. How-ever, if the serviceman desires, he canuse a 12F5, a 12SF5, a 50L6, and a35Z5 or a 45Z5; or if those tubes arenot available, he can substitute a 6Q7or a 6F5, a 6SQ7 or a 6SF5, a 25L6,and a 25Z6, in which case he will haveto use a line cord resistor to drop thevoltage for the tube filaments.

The filaments should be wired asshown with tube No. 1 filament con-necting to ground to prevent hum.

The tubes are used in this order:1-untuned detector; 2 -1st audio;

3-output; 4-rectifier.Various circuits were tried such as

using 12A7 as an untuned r.f. stageinto a 12SQ7 diode plate as a diodedetector, into the triode section of the125Q7 as first audio, but the resultswere not as good as the circuit shown.

How To Operate The TracerThe tracer is so sensitive that it is

not even necessary to touch an i.f. oraudio grid or plate-just place the prodnear the grid or plate and you can pickup a signal, the volume depending onwhich stage you are testing. In servicework I have found this tracer capableof picking up a signal over 3 feet awayfrom a dead set which had an openvoice coil in the speaker.

Stage gain can be checked by touch-ing the grid and then the plate ofevery stage working toward the speak-er.

An isolationtransformer is un-necessary becauseof the blocking

A B C

Front view of the hold -in -hand signal tracer.

condenser in the circuit. The volumecontrol controls the volume of both ther.f. audio and amplifier sections of thesignal tracer.

To operate tracer, plug into electricoutlet, touch an antenna to prod A ontop of tracer; if several stations comein at once, then it is all set. If a loudhum is noticed, reverse plug in outlet.

Testing procedure will depend onwhether set is inoperative or is noisyor fading. If set is inoperative, theshort prod is used. It consists of noth-ing more than a phone tip with a nailsoldered to it. The tracer is held in thehand because it only takes a fewseconds to touch a grid or plate ter-minal of a socket to determine if thatstage is working properly.

If set is noisy or fades, tracer canbe left on the bench and ordinary testleads applied to it to test the variousstages of the defective set. There willbe a slight detuning due to the longleads when this is done, but this doesnot interfere with the test that youare making. It may be necessary foryou to retune the, set a trifle.Set Testing Tips

When testing an a.c.-d.c. set, makecertain that the plug is inserted so thatthe chassis is connected to the groundedside of the line.

When testing a.c.-d.c. sets, only prodA should be used because both the set


Left-The tracer is inserted in the radio exactly like a probe.Below-A schematic diagram of the "Dynamic Handful" tracer.

JR,NAL

724c.oR 00/(1)

7:°....,..

,...q

-)

sb.

3 4.

C)-.----1- I

.1:::,..z7-.065 -.433255g.z1 5! 4.50.., IP:re nEio- rilBEK :OWRFPITOR iF

C4I--I-4 0001- IMO 452.5L'.100M,.

71...

1.....,230 (3) (2)(/) (4 ),c v. ...,..

.r.R14-7.PiATE r. REcr PLATE LMICORD

SWV:LN ---'altrre -r A / I

CONT...v.-. ,a,F(4,,bciN/N42526TIE 8orl I RLVEJAND CATI/OPEI ToqFpfER

6F5 65F56C7 1_ _WE Te/Opt_f 6147av J-- ALLT/oNI ONLY uzfy1.2A5 .001 12.fF5II-

400v (2)

25L6

0.541EyANA,"--

OUTPUT TRANI.50L6 vONJPEAKep

4/N. 41/AREOMAN( 11'24e6.0

OkouNa©To 1E7-.1

.03),144cov,910000V CONOTRAcek, Olof


ALL -BAND OSCILLATORThis signal generator uses plug-in coils to corer the spectrumall the way from 65 to 34,000 kilocycles without a break.

HIS signal generator has a con-tinuous range of 65 to 34.000 kilo-cycles. The signal may be modu-

lated by the a.f. oscillator which has acontinuous range of 24 to approximately20,000 cycles per second.

A small metal cabinet measuring 10x 6 x 7 inches provides the necessaryshielding for the oscillator. The r.f.Hartley oscillator uses a type 6J7 pen-tode radio tube. Intensity of oscillationis controlled by potentiometer R5 whichvaries the screen voltage. The switchmounted on R5 serves to turn off ther.f. oscillator when it is not being used.

If operated on a frequency below 2,000kilocycles, the output switch may beset for the i.f.-a.f. position. It was dis-covered that a stronger low radio -fre-quency output was obtained if thecoupling was not made directly to theplate of the oscillator. The a.f. outputconnection can be used for low radiofrequencies because the r.f. choke isolates the plate from the output connec-tion. The intensity of the oscillationsreaching the output leads is controlledby R10 at low radio frequencies andaudio frequencies; but when operatingon a frequency greater than 2,000 kilo-cycles, the output switch is set to ther.f. position and the intensity must becontrolled by the voltage potentiometerR5.

The condition of the 6J7 tube can bedetermined by connecting a 0-150 d.c.voltmeter across resistor R6 and chokeT1. The oscillator tube draws a largecurrent while not oscillating and a muchsmaller current while oscillating; there-fore, a large voltage drop reading will

indicate that the tube is not operatingproperly. If the grid cap of the oscilla-tor tube is touched, the reading willincrease providing the tube is oscilla-ting. If no meter is available, a roughcheck can be made by connecting amidget neon lampto the meter jacks.If the 6J7 is notoscillating, thelamp will glow. Itshould be notedthat the plate cur-rent flow will alsodecrease if thescreen voltage isreduced or the coilis removed.

Resistor R6serves to place theplate of the oscilla-tor tube at a lowerpotential than themodulator tube sothat more modula-tion may be se-cured. Either aplate couplingchoke or the primary winding of anaudio transformer can be used for T1.

The r.f. signal is modulated by turn-ing potentiometer R9 in a clockwisedirection from zero until the switch isturned on. The a.f. switch is set foreither external or internal operation.The external position connects the mod-ulator tube to the posts marked "Ex-ternal a.f. Source." A microphone orany other similar sound source may beconnected to these posts. The internalposition connects the other triode sec -

This commercial -looking signal generator has three sets of outputjacks, one each for r.f., for i.f.-a.f. and for the external voltmeter.

OUTPUTBLACK RED 45

I L'ORF."

OUTPUT SW. cr. RFC

tion of the 6C8 -G tube so that it formsa two -stage audio oscillator. The pitchmay be varied from 24 to more than20,000 cycles by the 1-megohm poten-tiometer R9.. This control serves as atone adjustment when the external posi-

L- 4.3 -laD =

FC4/ R4

VW' E -TYPE -

col L5

.1=CHASSIS

C6

EXTERNAL AF SOURCE V.M.BLACK RED BLACK RED

+o

+ --If

044.0--"-M-'7-/ ti0' 3525 C,I

SW.014 R9 / 1-

5t + -

0-

R2.j6J7 6C8 35Z5 $VVRIO.ON 17v.AC-DC

EL.

OMThe generator has a switching device which places two condensers inseries on the high -frequency bands. Audio tube is a multivibrator.

tion is used. If it is desired to test a.f.equipment, the output may be tappedby turning the output switch to the a.f.position. The intensity is controlled byR10.

A type 35Z5-GT radio tube is used asa half -wave rectifier. The circuit oper-ates from 120 volts a.c. or d.c.

Plug -ht Coil DataType "A" plitg-in coils have the 350 -

µpi tuning condenser connected direct-ly across the winding. Type "B" coils

The generator removed from its case. Eight plug-in. coils are used, intwo styles, so connected as to facilitate tuning over the wide range.

1947 RADIO -ELECTRONICS REFERENCE ANNUAL 17,

connect a small trimmer condenser,which is fixed at a certain capacity, inseries with the tuning condenser. Thehitter type is used for the high -fre-quency coil, but can be used on anyfrequency where band -spread operationis necessary or convenient.

Below -chassis and top

The coils are wound in four differentstyles. The first style consists of a self-supporting v.h.f. coil mounted inside astandard plug-in coil form. The secondis a single -layer winding. The third isa layer -wound coil. The first layer iswound directly on the form. This wind -

PLUG-IN COIL CHARTCOILNUMBERI -B -I

APPROXIMATEFREQUENCY

34 to I I Mc.

WINDING DATA

8 turnsSelf-supporting3/4" diameterTap 3 turns from GLarge stiff wire

WINDINGSTYLE

1

COILTYPE

B

OUTPUTSWITCH

R.F.

2-A-2 24 to 7.5 Mc. 41/2 turnsSpaced11/4" diameterCenter tapNumber 28 wire

2 A R.F.

3-A-2 14 to 3.5 Mc. 91/2 turnsSpaced11/4" diameterTap 5 turns from GNumber 28 wire

2 A R.F.

4-A-2 5 to 2.5 Mc. 17 turnsClose wound11/4" diameterTap II turns from GNumber 28 wire

2 A R.F.

5-A-2 2,500 to 900 Kc. 60 turnsClose wound11/4" diameterTap 40 turns from GNumber 28 wire

2 A R.F.(or I.F.)

6..A-3 950 to 390 Kc. 100 turns11/4" diameterNumber 28 wire

3

(2 layers)A I.F.

7-A-3 500 to 210 Kc. 200 turns11/4" diameterNumber 30 wire

3

(2 layers)A I.F.


3

(4layers)A I.F.


4 A I.F.

views, also cabinet and se+ of plug-in coils.

ing is covered with an insulating paperwhich is doped in place. The next layersare wound so that the winding endsdirectly over the place where the onebelow started. A paper strip is alwaysplaced between each layer. The fourthis a jumble winding which is spreadover the entire form.

The necessary data is given in thePlug -In Coil Chart. The center of thecoil is satisfactory for the tap if noother mention is made in the chart. Achange of a few turns up or down willoften make for smoother oscillation.

After the signal generator has beenconstructed and tested, it should be ac-curately calibrated. If no accurate sig-nal generator is available, the followingsystems can be used. Obtain an all -wavet.r.f. or superheterodyne receiver withan r.f. stage. If it has approximatecalibration and a tuning indicator, fairlyaccurate results are possible.

The low radio frequencies, 560 to 65kilocycles, are calibrated through theuse of the harmonics generated by theoscillator. Plug in the coil to be cali-brated. Disconnect the aerial andground wires from the receiver. Con-nect the leads from the output posts ofthe generator to the ground or chassisand the antenna. Set oscillator controlsso that it operates with a modulatedsignal. Turn the tuning knob to 100°.Several harmonics should fall withinthe broadcast band. If it is rememberedthat each harmonic is separated by afrequency equal to the fundamental sig-nal, it will be very easy to determinethe frequency of the oscillator. Forexample, if the oscillator were tuned to150 kilocycles, the harmonics would be150 kilocycles apart. The second har-monic wound fall on 300 kcs, the thirdon 450 kcs, the fourth on 600 kcs, thefifth on 750 kcs, etc. The fundamentaland first harmonic are identical. Justsubtract the smaller number from thenext larger. Six hundred from 750



RADIO LABORATORY

IN PORTABLE UNITThe facilities of a completeser% ice shop are included ina single easily -carried case.

THE housing shortage is no re-specter of persons. My radio hobbyand I had grown up together with

space unlimited. There was a largeroom to tinker in, a big work table,home-made instruments and apparatus,built with no regard for compactness.Then came a better job in a crowdedcity . . . and a four -room apartment.Also came a baby into our apartment,who in spite of her pint size occupiedat least one-half the space. There justwasn't room for so much as a variablecondenser to open out. My "junk" waspacked and stored in an old unheatedshed. But friends kept saying, "Wishyou'd take a look at my radio." Besides,I was getting mighty lonely for thefeel of a soldering iron. I began makingtrips to the shed. The photo shows theresult.

The whole thing tucks away into acloset when not in use but comes rightout into the living room in the eveningand perches on a kitchen chair in frontof the Chesterfield. There's room in thebottom for tools. The shelves at theright hold test prods, plug-in coils anda pocket volt-ohm-milliammeter. Thismeter is my one piece of "boughten"apparatus. In the lower left corner isa 110 -volt outlet (Fig. 1) controlled bythe switch just above it. There's apilot light shunted across the outlet(so you won't forget and leave thesoldering iron on). Above the switchis another outlet and there's anotherone behind the panel. The test instru-ments plug into it. This completes thefirst section. The apparatus is built insections on masonite backed with metalshields. Different sections can be re-moved senarately. Above the outlets isa four -inch dynamic sneaker. The audiochannel is located in the lower centralsection, with the off -on switch at theleft. Below the electron -eye is a neonbulb. To the left of the attenuator knob(below) is a single -pole double -throwswitch. This is shovrn in the diagramand explained later. The three pin jacksat the left are: Common, B -plus, and6.3 volts a.c. The two at the right areInput and Ground. The upper sectionwas built directly on the back of thepanel with no chassis but is carefullyshielded. The large dial above is fortuning. The pin jacks at the right arefor r.f. input (or aerial) and output.To the left is the regeneration controland two diode voltmeter pin jacks. Theupper is an a.c. innut and the loweris plus d.c. output. The plug-in coil canhe seen protruding slightly from behind

the panel at theright. When the lidis opened it can beused as a work-bench, the surfaceof which will notbe damaged byscratches, drillmarks or the scars from a hot solder-ing iron.

The Audio Channel

'The case contains

The circuit diagram is given at Fig.2. The unit consists of the loud -speaker,6V6 output tube, 6SQ7 voltage ampli-fier, 6E5 electron -ray voltage indicator,2-meg. attenuator and a switching ar-rangement. The switching arrangementallows one to listen to any audio signalor its effects may be noted on theelectron -ray indicator. The electron -rayindicator is especially useful in makingvoltage gain tests and in balancingphase -inverter circuits. It is sensitiveto frequencies above and below thelimits of the loud -speaker. The 6V6 ismuch superior to the more common6F6 because of its greater sensitivity,which is very valuable when listeningto weak signals. Voltage variations oflow frequency - hum, etc., cause theedge of the indicator -shadow to waver,flicker or blur. Frequencies above theaudible range to 50,000 cycles or moreclose the eye smoothly but no signal isheard from the loud -speaker. It shouldbe noted that when the speaker is in

instruments, receptacles and space for tools

the circuit the diode rectifier is inop-erative. If it were left in the circuitit would cause distortion. The 2-meg-ohm attenuator causes little loading inany circuit and allows a range of from1 volt to 500 to be measured. With goodbuilding and careful calibration thisunit will give accurate a.c. measure-ments which compare favorably withthose of a good electronic voltmeter.Strong i.f. signals are rectified by thisinstrument and close the eye smoothly.Even r.f. signals from a strong localstation have been picked up by a testprobe and have found their way to thegrid of the 6V6 and appeared as anuntuned and unwanted program.

The Neon Tester - shown in theAudio Channel diagram-needs no ex-planation. As a condenser tester it isthe most used apparatus on the panel.

R.F., I.F. and Signal GeneratorThis, as can be seen from Fig. 3, is

a simple one -tube regenerative circuitof the Hartley oscillator type. This isthe simplest and most satisfactory cir-cuit for this purpose. It has good

(Continued on pace 44)

.01

'''' I MEG'

..6V6 : (.r.

II7V. ACc-I(-

2 MEGS

6SQ7 1

.L.. 5

6E5 Mt/"Th

.5mEG i i_..-

_,..Z

To1,111 -ac 4

\7_,..-su

'.2 VOICECOI L

OUTAt

oLET

IAN

§:''

.200I.

5Y41.

SPEAKERFIELD

50,000

PePILOT OUTLET

LINE ..--''. 8 8 8 NETEONR.10.N..-le

TESTER

I

e. The AUDNO CHANNELFIG.1. FIG.2

OSCILLATOR- .000fSIGNAL I M EG

6SKT .os 1 V DIODETRACER. -. I \ RECTIFIER

4002,5 AC INPUT Io --II

PLUG-IN

.0002.5STANDARDTUNING COND.

--.167., .25 MEG

DC+CALL 8 2. PAPER

To DC VOLTMETERa.

XCOND.

DC -

---.25ME G .-'r I B+

FIG.3 FIG.4


BREAK 55 60 70 8091110 1301501.7olkAA

AC-DC ON OFF ON-BATT.

VOLUME PO ER. TONING

RADIOS SERVICEDSight, hearing, touch, smell and tasteare valuable instruments for servicingradio receivers and electronic devices

DURING about fifteen years of radioservicing I have noticed many begin-ners (and some not beginners!) tinker-

ing with radios and getting nowhere. I haveworked with a few so-called "engineers" andhave seen them search for many hours todiscover trouble that would have been ap-parent at once if they had but used theirknowledge and observed some things thatare quite plain to see.

Careful observation will locate at leastseventy-five per cent of all radio troubles.The following system is one I use all thetime, and it leads me to the trouble quickly,in most cases. Oldtimers will agree thatobservation is well worth while, but be-ginners will find the system something theyhave wished for since they first becameinterested in "fixing" radios. These instruc-tions are not likely to be of much use to theman who has so much confidence in hisnative luck that he plunges into a radiochassis with screwdriver, pliers and solderingiron and really "fixes" the set-so that itneeds rebuilding!

All information is as brief and as non-technical as possible so that the novice mayderive all possible benefit from the informa-tion given.

Let us suppose that we have a six- to ten -tube superhet on the bench and that we arepreparing to analyze the trouble. However,this system may be adapted to any othertype of circuit also, with proper consideration

given to certain differences of circuit action.1-First, see that all tubes are in their

proper sockets. Often the owner has re-moved the tubes for testing (for free) andfrequently replaces them in the wrongsockets.

2-Next, turn on the set. If tubes do notlight, check line cord for breaks. On portablesespecially, check the switch. 3-Watch therectifier tube for signs of over -heating, platesturning red, etc. Check for shorted filtercondensers, shorted sockets or shorted trans-former windings. 4-Turn chassis over andlook for wires touching, burned -out resistors,etc.

5-Have the dial set on a strong localstation and the volume control set at maxi-mum position. 6-Touch the grid cap of thefirst audio tube, or the grid terminal. Thisusually can be easily located as the grid leadcomes from beneath the chassis. In the caseof the single -ended tubes, touch a test prodto the center of the volume control to getthe same results as though your finger wereplaced there. A loud clear buzz should beheard if all is well in the audio end. 7-Ifnot, pull out the power tube. It should makea thump in the speaker if there is voltageon the plate of the tube. 8-If not, check thevoice coil. 9-On midgets, make sure thepilot lamp is O.K.

10-Feel the output transformer. Theseoften become warm when excess current isflowing through the plate winding. 11-The

1300lno:;,-;11.


BY OBSERVATIONsmall tone -compensating condenser connectedfrom plate to cathode (or ground) may beshorted. Disconnect it and see. Or the coup-ling condenser may be leaking a positivevoltage to the grid, causing the tube to drawexcessive current.

12-Listen closely to the speaker. Thereshould be some hum if there is any voltageat all on the power tube. If it is entirelyquiet look for an open voice coil or brokenleads to the voice coil. 13-Listen to theoutput transformer. You can hear it singingif the voice coil circuit is broken.

14-Watch any tuning indicator that maybe present. If it indicates a signal the r.f.end is probably O.K. Electron -ray indicatortubes appear to burn red when no voltage issupplied to their anodes.

15-Have a test prod on the lead-in froma long antenna. Touch the grid of the i.f.tubes. Noise coming through will indicatethe stage is in passable condition. Workback toward the antenna post. 16-Turn thewave -band switch to be sure it is set onthe broadcast band. If the noise still comesthrough, but no signal, the oscillator is per-haps not functioning. 17-Occasionally astrong signal will force its way through thei.f. section when the oscillator has stopped.You can double-check this by connecting thetest oscillator to the grid of the first detectortube and setting it at a frequency of a localstation plus the i.f. frequency of the receiver.The signal will come through if that is youronly trouble.

18-Try adjusting the i.f. compensatingcondensers to be sure some home mechanichasn't discovered they were loose and screwedthem down tight. Mark the original settingand don't turn them far off without returning

to the original-especially if you have notest oscillator.

This procedure should not have taken overfive minutes, and the service man should, witha little reasoning, have a good idea as towhere the trouble lies-at least, in whichstage it lies.

19-If you are without the test oscillator,you still can do a fair job of alignment on areceiver by using the noise pickup of yourantenna. If you should be so (un)fortunateas to have your shop in an interference -freelocation, generate noise with a buzzer orspark coil.

Set the dial at a point where no stationis heard. Turn up the volume control andadjust the i.f. trimmers for the highest noiselevel. The noise has very little effect on thea.v.c. action and accurate adjustment can bemade in this manner. 20-Next, tune in astation on the high -frequency end of the dialand adjust the oscillator trimmer until thestation is received best. Move the dial offthe station and adjust the r.f, trimmers formaximum noise level. Lastly, set dial at thelow frequency and adjust padder for maxi-mum noise. The broadcast band is nowaligned.

(This system will work only on sets withfixed padders in which no accident hascaused the oscillator frequency to be "off."Where the padder has been screwed down sothat the intermediate frequency generatedby the oscillator is-say-300 kilocycles, anattempt to align will leave the i.f. tuned to300 kc instead of the normal 450-465 usedon most radios. The result is that stationswill come in only on that part of the dial at


WAVE BAND SWITCH

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MY LYONOVI/01/

hi ImIad du du

-:-.1111111111111111111/1111111111111,


POCKET RADIO CHECKER

Widerange Tester.Power consumptionis measured throughreceptacle on top.

FAVERwish for a small pocket

tester that would do a man-sizedjob? This meter not only covers

the regular ranges, but has condenserand alternating current measuring fa-cilities. Power -line -operated devices areeasily checked for correct current drainwithout opening their line cords. Threeswitches are incorporated in the circuitto provide a minimum of test leadchanges and to increase safety factorwhen making tests on the power line.

10V. AC C X 10

10V. DC

4500100K 2W.

100V C X 100 o

31( .01

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10 MA, DC

°.15 AMP. AC

,.,100 MA DC"1.5 AMP. AC

01 AMP. DC15 AMR AC

1--0-0RX 14.5V.

-oR X10

Fig. I7 -Schematic of the Widerange Tester.

A neat multitester with settles for capacityand a.c. amperes as well as the usual ranges

Selecting the meter ranges was oneof the main problems. A compromisebetween versatility and size and costwas our objective.

We first tackled the voltage ranges.Examination of the problem revealedthat a 1 -volt d.c. range would be use-

less, as battery voltages start at 1.5volts. A 1 -volt range a.c. meter canbe used for numerous testing pur-poses. This range serves as anexcellent output indicator across

voice coils, thus facilitating receiveralignment and signal tracing.

Similar pros and cons made us de-sign the voltage measurements to in-crease in multiples of ten. Reading isthus simplified by having one row ofnumbers on the scale instead of several.The voltage ranges thus became 10, 100and 1000 volts, a.c. or d.c., with the-addition of a special 1 -Volt a.c. range,as mentioned above.

Milliammeter ranges were alsochosen in multiples of 10, for simplescale reading. 1, 10, 100 and 1000 milli-amperes (1 ampere) will cover mostservice requirements.

Alternating current ranges weremade to operate on the same currentshunts used for direct current readings,resulting in fewer switching positions,smaller size and less shunt winding.Three alternating current ranges covermeasurements from 50 milliamperes to15 amperes.

A trouble with most pocket testers isthat the ohms zero adjustment has tobe reset every time the range switchis moved. This bothersome procedurehas been minimized to the extent thatno resettings are required when freshbatteries are used. Actually the a.c.power line can be used in place ofbatteries, but then resistance measure-ments cannot be made in the absenceof power lines.

Resistances are measured in threeranges: 0 to 10,000 ohms, 0 to 100,000ohms and 0 to 1 megohm, and are allfound on the same meter scale. Theseranges can be extended if a 45 -voltbattery is added in series with a 45,000 -ohm resistor and the 1-meg range,which will now measure 0 to 10megohms.

Next on our list of ranges is capa-city. For these measurements a sourceof standard frequency is necessary.This is obtained from the a.c. powerline. Very convenient ranges availablefor these measurements are: .001 to .1microfarad, .01 to 1 microfarad and .1to 10 microfarads. These ranges fallin the same positions as the 1, 10 and100 volt a.c. positions on the selectorswitch. For operation the plug must be

connected to the a.c. power line, and ca-pacity is measured between the jacksmarked CAPACITY and PLUS.

To measure approximate wattageconsumption, electrical equipment isplugged into the meter receptacle. Pow-er is obtained by means of a cordwhich is connected to the power line.Before power is applied the range anda.c.-d.c. switches must be set. Powerand meter indications are obtained si-multaneously by pressing the push but-ton. For apparent wattage, currentreading is multiplied by the line volt-age. See Fig. 1.

It must be stressed that these read-ings are only approximate for a.c. watt-age, as power factor is not taken into .account in our calculations.

Construction and PartsFirst on the list of material is a 3 -

inch, 1 -ma milliammeter with an inter-nal resistance of 55 ohms. If a 1 -mamilliammeter of smaller resistance isobtainable, then simply adding enoughseries resistance to make 55 ohms willdo.

Three switches are necessary. Oneeleven -position, two -gang switch is re-quired for range selection. The a.c.-d.c.changeover switch is of the d.p.d.t.toggle type. The power line switch forcurrent and wattage measurement isthe push to close variety.

To obtain maximum a.c. sensitivityand linearity and still use a 1 -ma meter,the full -wave bridge type meter rectifieris employed.

The case for this tester was home -constructed. Bakelite is used for theentire box. Two thicknesses are nec-essary. The panel and bottom measure


The insulated bracket holds the battery clear.

22 194.7 RADIO -ELECTRONICS REFERENCE ANN UAL

DIODE CRYSTAL PROBE

THE majority of present-day vac-uum -tube voltmeters are essen-tially d.c. indicating devices. A

rectifier unit is employed to permit mea-surement of a.c. voltages.

Many factors influence the choice ofthe rectifier unit and its arrangementwith respect to the d.c. indicator. Sinceoperation over a wide frequency rangeis desirable, it is necessary to make alla.c. leads as .short as practicable. More-over, linear rectification is preferableso the d.c. indicator deflection will bedirectly proportional to the magnitudeof the a.c. voltage.

HOT

DIOD

INPUT

Iu -

GROUND0 0

Fig. I-Diagram of standard type diode probe.

A vacuum -tube diode rectifier, mount-ed in a convenient probe and arrangedto feed the d.c. section by means of ashielded cable, is admirably suited tothis purpose.

A wide variety of small vacuum tubesmay be conveniently used. In general,it is necessary to choose tubes having alow input capacity. Thus the input im-pedance will be sufficiently high to pre-clude loading of the external circuit.

With the advent of the new germa-nium crystal diode (Sylvania 1N34),the constructor has a useful devicewhich simplifies probe design. Most ofthe disadvantages of vacuum -tube di-odes are eliminated.

A comparison of .Figs. 1 and 2 willshow immediately the simplicity of thecrystal version. Fig. 1 illustrates atypical vacuum diode circuit. Fig. 2shows its crystal counterpart. Notethat a small battery and variable re-sistor are needed to balance out thecontact potential of the diode. The prop-erties of the germanium crystal havebeen adequately described in the liter-ature.* Hence no attempt will be madeto discuss the theory of operation. Anactual probe will be described.

The probe is simple to fabricate. Itwas built into a small penlite flashlightcase, details of which may be seen inthe photo. It may be used in con-junction with practically any d.c. vac-uum -tube voltmeter and with manysignal tracers. Note the extremely

' See 'Germanium Crystal Diodes"-Cornelius.Electrunics, February, 7946. -

"HTF.. Crystal Dindes": -1.enne, R Amu -CRAFT.March, ]946

This crystal diode head makes a signal tracerout of your own vacuum -tube voltmeter.

small size. The circuit is that of Fig. 2.The capacitor C is .01 icf and the func-tion of R is taken over by the dividerresistors across the input of the vacu-um -tube voltmeter. In operation themeter is set up to measure negatived.c. voltage. Full scale meter reading of1.5 volts d.c. may be obtained with theArcuit of Fig. 2 when 1.5 volts a.c. is ap-plied to the probe. To increase the d.c.output voltage, the value of C must beincreased. A value of .01 ,uf or less is tobe preferred, however, in order to keepthe input impedance at a high value.

An exploded view may be seen in thesecond photo. The front row of this pho-to shows (left to right) the capacitor, C,as it is soldered to a short length ofpointed No. 8 wire and the tiny crystaland its mounting. The bakelite tubingfitted into the plastic case cap and thecase proper are shown in the secondrow. In the background of the firstphoto rests the 7 -prong plug whichfeeds the d.c. indicator.

The crystal will operate well at fre-

quencies as high as 100 mc. The input

HOT Co --It _L o_INPUT XTAL .... OUTPUT

GROUNDCARTRIDGE +a a

Fig. 2-A diode probe with germanium crystal.

impedance of the unit shown was foundto approximate one megohm at 1000 cy-cles per second. The output is non-lin-ear on the lowest range and the metermust be calibrated accordingly. A linearscale, however, is sufficiently accuratefor most purposes.

It is to be emphasized that the a.c.voltage applied to the probe must belimited to somewhat less than 50 volts.To double the applicable voltage, twocrystals may be used in series.

The above material is consideredmerely suggestive. It is hoped the ex-perimenter will find many new uses forthe crystal. Doubtless, variant circuitscan be adapted to special requirementsto suit the user.

The crystal probe in its small penlite case.

Exploded view of probe. Crystal is at center.


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NOMOGRAM PRINCIPLESANOMOGRAM (Greek: A law writ-

ten down) is a chart made up ofa number of lines calibrated to

represent quantities in the problems tobe solved. A straightedge is laid acrosstwo of the lines. The answer to theproblem is found where it intersects athird line. Most of the commonest radioproblems can be put into nomographform, hence this type of chart is one ofthe most useful to radiomen.

This principle of the nomogram issimplicity itself. Fig. 1 shows a typicalone, for adding figures from 1 to 10.The outside lines which represent thenumbers to be added, may be 10 incheslong, divided into equal parts (inches).The totals are found on a line drawnmidway between the two.

To calibrate the center line, lay aruler across the tops and bottoms of thetwo outside ones. Because 0 plus 0 = 0,the base of the center line is 0. At thetop, 10 plus 10 = 20, and the line is somarked. Dividing the center line equallygives us 20 divisions spaced one-halfinch apart. If a ruler is now placedacross the two 5's on the outside lines,the sum 10 will be read on the centerone. Try 5 plus 8 or 9 plus 1.

Multiplication LogarithmsThe chart above is hardly useful-

it is easier to do the additions mentallythan to use the chart. The nomogrambecomes valuable when applied toeqUations like the familiar

1

1=6.28 V LC

Such application is possible becausemultiplication and division can be trans-

-10

-9

-8

-7

-6

-5

-4

-3

-2

-20-19

- 18

-17

-16

-15

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-13

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-II-10

-0-8--6-5

-3-2

- 1

10-

9-

8-

7-

6-

5-

4-

Fig. I-The fundamental type of nomogram.

formed into addition and subtractionby means of logarithms. These are num-bers so proportioned to ordinary num-bers that the sum. of the logarithms ofany two numbers is equal to the loga-rithm of their product. For example, add-ing the logarithm of 5 to the logarithmof 6 gives the logarithm of 30.

If we construct a chart like that ofFig. 1, using the logarithms of numbersfrom 1 to 10, we have a -nomogram thatcan multiply. Simplest of all multipli-cation nomograms is the product of twowhole numbers-the logarithmic equiv-alent of Fig. 1. A chart for the commonradio equation IR = E (Ohm's Law)is set up in Fig. 2.

Nomogram A is a more practicalgraph. The two outside scales run (ineffect) from 1 to 100 instead of 1 to10. The center scale can then run from1 to 10,000 (in this case, from 0.1 to1,000). A nomogram of this type can beused in many practical radio problems.

Nomograms for all radio uses can beconstructed with the help of a smallsupply of logarithmic cross-section pa-per, which can be bought at almost anystationery or draftsman's supply house.It is well to get a few sheets of "1cycle x 10 divisions per inch" as wellas a smaller number of 2 -cycle and 3 -cycle sheets (also 10 divisions per inch).Some tracing paper completes the out-fit. Lacking logarithmic paper, a cheapslide -rule may be pressed into service.(The slide -rule is a perfect example ofa logarithmically divided scale.)

The simple chart of Fig. 2 can bemade with a piece of 1 -cycle and apiece of 2 -cycle paper. Lay a piece oftracing paper over the 1 -cycle sheetand trace the two outside lines. Themiddle line is traced from the 2 -cyclepaper.

More Difficult ProblemsMost nomograms express more com-

plex problems than the simple IR = Ejust described. A common radio problemis: "With a given amount of currentthrough (or voltage across) a resistor,what is a safe wattage rating?" Themathematical formula is PR W(watts). The difference between thisand IR = E is that we have a powerof a number to contend with. 12 cannotbe handled like simple I, but is easy todeal with on a pornographic chart.Multiplication is expressed logarithmi-cally on the chart by simple- addition.Powers are expressed by multiplication.The scale for 12 is simply I X 2, ortwice as long as a scale for I wouldbe. 14 would be four times as long.

Nomograms with scales of differentlengths would be cluMsy. By making thetwo outside scales the same lengthand displacing the product scale as in

Nomogram B, the same result isachieved. The scale can be positionedby selecting a value-say 1 watt-and finding it with two sets of factors-say 10,000 ohms by 10 milliamperesand 100 ohms by 100 ma (0.1 ampere).The intersection of the two indicatesthe position of the wattage scale.

To construct this nomogram, twosheets of 1 -cycle paper ,are used foreach outside- stale, permiting the six -cycle wattage scale to be laid out with3 -cycle paper. Top and bottom cyclesare not used, as the quantities are out-side the range which would be usefulto a radioman.

Nomogram C (next page) is an ex-ample of a scale in which the finalfigures are not the ones on which thenomogram is calculated. The equationis: R k/C.M., where R is ohms perfoot, k is the speci_Ac resistivity of thematerial and C.M. the wire cross-sectionin circular mils. Since we are interestedin wire sizes rather than circular mils,AWG (B & S) wire size numbers areinserted and the C.M. figures erasedafter the nomogram is completed. Thesame thing might have been done onthe other outside scale, leaving onlythe names of the wire material withoutincluding the resistivity.

Another new departure appears inNomogram C. Since we must divide byC.M., that scale is turned upside down,running in the opposite direction tothe other two.

All three lines of Nomogram D (pege26) are drawn to the same scale. Thisis because we are dealing with theproducts of the square roots of capa-


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9--10

-87--6-5

-4

-3

-2

3-

_

2 -

Fig. 2-Most nomograms are forms of this one.


WIRE SIZE

looCMo- 20OHMS METAL

SILVER- 9.56COPPER -1035

--

100-CM

-21

- 22

- 23

- 24

25

- 27

- 28

=29

30

-1.06

-.02

-.03

-.04

-.05

-.07-.08

.6

=1.0

ALUMINUM

ZINC

NICKEL

STEEL

-17

-35

-60

-100

- 31

-2- 32

-3- 33 -4

WIRE SIZE OHMS METAL -5-'COPPER- 34 10.35

-7 MANGANIN-264-8- 35 .1

.105-9

10CONSTANTIN-294

28- 36 2930, loo - 20 MATER/AL

- 37 SIZE AND

- 30RES/STANCEOF WIRE- 38 - 40

- 50

- 39 - 60

-I- 70

80

10- 40 1100 RADIO -CRAFT, 7,46CM

NOMOGRAM C

411f

-1000-950-900-850-800-750-700-650-600-550-500

-450

-400

-350

-300

-250

-200

-150

-100-95-90- 85-80-75-70-65-60-55-50-45-40

-35

-30

-25

-20

mut

1006

uh

Kc

-160

-175

-200

uh

1000-950-900 -850-800 -750-700 -

-250 650-600-

-300 550-500-

-350 450--400 400-

-450350

-500-550 30Q

-600-650 250

-700-750-800 200-850-900-950-1000

150

-1250

-1500100 -95 -90 -85--2000 80-75-70-

-2500 65-60-

-3000 55-50-

-3500 45--4000 40-250-4500 35--5000-5500 30--6000-6500-7000 CAPAC/TY-7500-8000=8500

FREQUENCY.AND 20 -

-9000-9500 INDUCTANCE--10,000

-11,000 15=

-12,000-13,000-14,000-15,000-16,000 RADIO -CRAFT, 7, 46 10-

NOMOGRAM D

A DECIBEL NOMOGRAMWiost useful of graphic charts, the HOMO, -

gram is "equivalent to an infinite numberof graphs." This one eCTIDI be used to finda number of solutions to decibel problems

xrANY problems may be solved bygraphical means. An advantageof such representations is the

bird's-eye view which results. To con-nect twO variables it is common to plota chart which is a line or curve, everypoint of which indicates one variablein terms of the other. Charts may bedesigned to correlate frequency vs. dialsetting, antenna length vs. reactance,plate voltage vs. plate current, etc.

Another type of graph is the nomo-graph, which is useful in certain tyresof problems. This is usually designedto contain three lines or curves, eachcalibrated in terms of a variable. Thenomograph differs from the ordinarychart in that the reader supplies hisown indication by the use of a straight-edge, preferably a celluloid or othertransparent ruler.

Suppose we wish to show the varia-tion of three quantities: Two may beshown on a chart, but there is no wayof showing the third, which will haveto be assumed constant. We wouldneed an infinite number of curves onour chart,, each corresponding to somevalue of the third variable. ..1 nomo-graph is therefore equal to an infinite num-ber of graphs. This is the key to itsusefulness.

A useful nomograph is that relating(lb gain or loss to voltage or powerratio. The three variables are input,output and decibels. In the figure, theleft-hand scale is calibrated in valuesfrom 1 microvolt to 100 volts in twosections, A and B. The right-hand scaleindicates from one-half volt to 500volts. The center scale shows decibelsin two sections, C corresponding to Aand D corresponding to B.

As the nomograph stands it indicatesvoltage gain or loss, but since currentvaries directly with voltage in any con-stant impedance circuit, amperes maybe substituted for volts and micro-amperes for microvolts. To extend topower values the center scale must bedivided by two for all readings.

To work out .a problem, connect thelarger of the two voltages, currents orpowers at scale E with the smaller ateither A or B by means of the ruler.If the output is larger there is a gain,otherwise a loss. The answer is read offat C or D.

Five lines are shown on the figure asexamples.

1-We wish to find the voltage gain

of an audio amplifier. Making measure-ments with a v.t.v.m. we find the outputis 55 volts when the input is .15 volt.There is a GAIN of 51.3 db (Line A).

2-We have an r.f. tuner and afterrepairing and aligning we wish to fins.its amplification. Applying a signalgenerator to an artificial antenna wefind an output of 3 volts when 1600

microvolts is measured at the input.The GAIN is 65 db (Line B).

3-flow much attenuation must weuse to obtain an output of .51 voltwhen 20 volts is applied to the atten-uator ? All impedances are assumedmatched. We must design an attenua-tor to have a 31.9 db loss (Line C).The same line may be used to show theoutput when the input and the attenua-don are known.

4-As mentioned before, power cal-culations are the same except that thedb scale is read off as one-half itsvalue. The catalog lists a particularamplifier as having 10 watts output.What is its power gain (above 6 milli -watts) ? Connect 10 at E with 6009 atA. The gain is 64.2 divided by 2, equals32.1 db (Line D).



FREQUENCY-WAVELENGTH CHART

Mc Cm Mc Mtr Kc Mtr30,000 I 300 1 3,000 100

.-.-J-2004-1.5 2/20,000 1.5 000 150

___,-

-#-- _- ._-=-,--

_,-_,-- _,-

_.----1.:

15,000 - 2 150 1: 2 1,500 -7: 200:.../- 1._,-_...- - -- --- _,-

7.10,000 3 100 _

---,

3 1,000 300_9,000--90- 900-1 r --8,000- 80- 800---4 -4 -4007,000 --- 70- 700-- ../- __/-

6,000- 5 60-5 600 500

5,000 -.-- 6 50-6 500 600-r ..- __/-

- 7 -7 -7004,000 - 40- 400--8 -800-9 -9 -900

3,000 - 10 30 _10 300 1,000- - -

2,000 - 15 20-15 200 - 1,500

1,500 -20 15 20 150 2 000-

1,000 .."-30 10 E30 100 - 3,000900- 9- 90800- 8- 80--40 ---40 -4,000700 - 7- 70-

-r- _r- -r-600 50 6 50 60 5,000

- .- --.- -s-.500 60 5 60 50 6,000

-/- -d--- -r-- 70 -70 - 7,000400 - 4- 40-- 80 - 80 - 8,000- 90 -90 F. S, - 9,000-

300 -:-100 3-100 7/25/46 30 10,000

Mc Cm Mc Mtr Kc Mtr28 1947 RADIO -ELECTRONICS REFERENCE ANNUAL

COIL DESIGN NOMOGRAMTo use the nomogram, connect thethree known values as shown in

the key, then read the fourth one. Forexample, a 11/2 -inch diameter coil form

12 10-

10

9

8

11/2

3/4

1/2

15

20

25

30

40

26 shows that 250 1.11 will be ample.A straightedge is laid on the nomo-gram so that it intersects 11/2 on the"d" and 250 on the "L" scale. A light

50 -D_ -

60

70

80

90

100

150

is available, with space enough to winda coil 11/2 -inch long. A coil which willtune across the broadcast band with a.00035 (350 nuf) variable condenseris needed. Reference to the inductance -capacity -frequency nomogram on page

-L--

which will wind 70 turns per inch isneeded. The wire table on page 32gives 72 turns per inch for size 28,which is therefore the size required

KEY lc

mark is made where it crosses thereference line. The straightedge is nowplaced so that it intersects 11/2 on the"1" scale and crosses the reference lineat the mark. It will be found to inter-sect the "n" line at 70. Therefore wire

lc L

-20

-30

-40-50-- 60

-- 80

=100

-- 150

=-200

- 250

=300

-400- 500

-600

-800

7=1000

-1500

=2000

-3000

-4000

for the given coil.This universal chart will serve for the

design of single layer coils from theshort waves to intermediate frequen-cies, and can even be used for largetransmitting coils.

1947 RADIO-ELEeTHONICS REFERENCE ANNUAL 29

CAPACITOR MARKINGSSeveral Systems of Capacitor Marking have beenused in recent years. They are described here.

TABLE I. BASIC THREE -DOT COLOR CODE.

First Second Third Toler - Volt-Color Dot Dot Dot ante ageBlack 0 0 none 20%Brown I I 0 1% 100

Red 2 2 00 2% 200

Orange 3 3 000 3% 300

Yellow 4 4 0,000 4% 400

Green 5 5 00,000 5% 500

Blue 6 6 000,000 6% 600

Violet 7 7 0,000,000 7% 700

Gray 8 8 00,000,000 8% 800

White 9 9 000,000,000 9% 900

Gold * divide by 10 50/ 1,000

Silver * * divide by 100 10% 2,000

(body) * ,, 20% (lowest)

*not used.

EXAMPLE: A 0.003-0: (6,000-nuf)capacitor is marked by three dots insequence as follows: blue (6), black(0) and red (00).

TABLE II. RMA SIX -DOT COLOR CODE

FirstSec -and Third Fourth Fifth Sixth

Color Dot Dot Dot Dot Dot DotBlack 0 0 0 noneBrown I I I 0 I% 100-vRed 2 2 2 00 2% 200-vOrange 3 3 3 000 3% 300-vYellow 4 4 4 0,000 4% 400-vGreen 5 5 5 00,000 5% 500-vBlue 6 6 6 000,000 6% 600-vViolet 7 7 7 0,000,000 7% 700-vGray 8 8 8 00,000,000 8% 800-vWhite 9 9 9 000,000,000 9% 900-vGold * * divide by 10 5% I ,000-vSilver * * divide by 100 10% 2,000-v(body) 20% 500-v

*not used.

EXAMPLE: A capacitor of 0.006-uf(6,000rtuf) plus -or -minus ten per cent,800 -volts D.C. working voltage, ismarked as follows: blue (6), black (0),black (0), brown (one additional zero),silver (10%) and gray (800-v) in thatorder.

TABLE III AWS SIX -DOT COLOR CODE FORMICA CAPACITORS

1st 2nd 3rd 4th 5thColor Dot Dot Dot Dot Dot Sixth DotBlack 0 0 0 none 20% No specified qualities.Brown * I I 0 * Specified "Q".Red * 2 2 00 2% Temperature coeffi-

cient: plus -or -minus200 parts/million/C°.

3 000 * Temperature coeffi-cient: plus -or -minus100 parts/million/C'.

* 4 4 * Temperature coeffi-cient: 0 to plus 00parts/million/C°.

* 5 5 * Temperature coeffi-cient: 0 to plus 50parts/million/C°.

* 6 6 * Temperature coeffi-cient: 0 to minus 50parts/million/C°.

Violet * 7 7

Gray * 8 8 * *White * 9 9 *Gold * ° * divide 5%

by 10Silver * divide 10%,

by 100

Orange

Yellow

Green

Blue

*not used.

3

(When the AWS standard is appliedto molded paper capacitors, the firstdot-always black in a mica condenser

DOT DOT DOTI 2 3

OR

VOLTAGE NO TOLERANCERATING COLOR

VOLTAGE NORATING COLOR TOLERANCE

DOT DOT DOTI 2 3

Basic 3 -dot color code provides working voltage and tolerance indications.

DOT DOT DOTI 2 3

MARLII; W MAL:

DOT DOT DOT6 5 4

The RMA six -dot color code. See Table II. The AWS mica capacitor code. See Table III.

DOT DOT DOT6 5 4

-is silver, as is the fifth dot. The sixthdot indicates operating temperaturerange: brown, from minus 67 to plus167 degrees; and black, from minus 67to plus 185 degrees.)

DOT DOT DOTI 2

reLAARLIV,

DOT DOT DOT6 5 4

AWS paper capacitor code. First and fifthdots are always silver, sixth black or brown.

EXAMPLES: A 0.00012-g (120-mi,f) capacitor is marked, to indicateits value, as follows: black (0), brown(1), red (2) and brown (one additionalzero).

The fifth dot in the AWS color codeindicates the capacitance tolerance inper cent of rated capacitance as prev-iously described. The sixth dot, intro-ducing a new factor, denotes character-istics of design involving Q -factors,temperature coefficients, maximumdrift limitations, and production testrequirements.

Tubular Ceramic CapacitorsEXAMPLE: A 30-auf plus -or -minus

5% capacitor with a temperature co-efficient of 80 parts per million per de-gree Centigrade would be marked asfollows: end band or dot, red (80 parts/million/C°) ; second color, orange (3);third color, black (0); fourth color,black (no additional zeros); and fifthcolor, green (plus -or -minus 5%).

TIP DOT DOT DOT DOTI 2 3 4

The RMA code for tubular ceramic capacitors.

The symbol (negative) indicates thatthe capacitance varies inversely withtemperature. The temperature coeffi-cient is expressed in micromicrofaradsper microfarad per degree Centigrade.Some capacitors are marked with anumeral instead of a color code. Forexample, N-030 represents a negativetemperature coefficient of 0.00003-uuf/nif/C°.

30 1947 RADIO -ELECTRONICS REVERENCE ANNUAL

LAWS OF THE ATOM1. A single ATOM is the tiniest particle

of any chemical element that can exist byitself and retain the qualities that mark itas that element.

2. All material things in the universeknown to our senses are composed of oneor more CHEMICAL ELEMENTS.

3. Substances composed of more thanone element are known as COMPOUNDS.Atoms of elements are held together incompounds by electrical forces in the outerparts of their structure.

4. The smallest unit of a compound, usu-ally composed of two or more atoms, isknown as a MOLECULE.

5. There used to be 92 chemical elements,from hydrogen (ilU) the lightest, to urani-um (92U238), the heaviest. There are nowtwo new elements, NEPTUNIUM (93.Np239)and PLUTONIUM (94Pu239).

6. When elements are reprasented, asabove, by their chemical SYMBOLS, thesubscript number is the atomic number.This is different for each element. Thesuperscript number represents the atomicweight.

7. One of the qualities characteristicof matter is weight or mass. ATOMICWEIGHT is expressed on a relative scale,as compared with the weight of hydrogenwhich is taken as one.

8. ATOMIC NUMBER is the measure ofthe electric charge on the nucleus of theatom's mass.

9. Different samples of the same element,when tested by chemists, are sometimesfound to have different atomic weights.Lead which occurs with radium, for ex-ample, has a different atomic weight fromordinary lead.

10. In all other ways the two kinds oflead are chemical twins, exactly alike ex-cept for weight. Elements which differ inweight only are called ISOTOPES.

11. Uranium has several isotopes. Theusual kind, whose atomic weight is 238,was used to produce the two new elements.U-235 was used to make the ATOMICBOMB.

12. Each of the new elements, neptuniumand plutonium, has two isotopes whoseatomic weights are 238 and 239.

13. Different elements, quite distinct inchemical behavior, may have the sameatomic weight. We have 9211-238, 9aNp-238and o4Pu-239

'

all with different properties.Such elements are now called ISOBARS.

14. All atoms are composed of standardinterchangeable parts. These are PROTONS,NEUTRONS and ELECTRONS.

15. Protons and neutrons make up theNUCLEUS of the atom. The structure ofthe atom is much like that of the solarsystem. The nucleus corresponds to the sunat the center. The planets are electrons re-volving in their orbits.

16. The proton and the neutron each havea mass about equal to that of a hydrogenatom, which is 1 on the chemist's scale.Each is about 1800 times heavier than theelectron.

17. The ELECTRONS, light in weight andsome distance away from the heart ornucleus of the atom, revolve around thenucleus much as planets revolve aroundthe sun. They are held in their courses byelectric attraction.

18. The proton has a POSITIVE chargeof electricity, the electron has a NEGA-TIVE charge equal and opposite to -thepositive charge of the proton. The neutronhas no charge at all.

19. The difference in chemical propertiesof the elements is caused by difference inthe number of protons in the nucleus. Thisis the ATOMIC NUMBER.

20. Atomic weight is the SUM of theweights of the protons and neutrons in thenucleus.

21. It is the NEUTRON which figures inthe transmutations which give atomicpower. Neptunium and plutonium wereformed by bombarding uranium 238 withneutrons.

22. Neutrons can PENETRATE to thenucleus of heavy atoms when charged par-ticles would be repelled by charges in theatom.

23. The HYDROGEN atom is believed tohave just one proton as its nucleus, withone electron circling around it. Hydrogen'satomic weight and atomic number are eachone.

24. Hydrogen has one isotope which isjust like ordinary hydrogen except that itis twice as heavy. It is known as "heavyhydrogen" and sometimes as DEUTERIUM.Its compound with oxygen is called "heavywater."

25. The nucleus of HEAVY HYDROGENcontains one proton and one neutron. Theatomic number of heavy hydrogen is one,corresponding to one proton. The atomicweight is two, corresponding to the twoheavy particles, proton and neutron.

26. HELIUM has two protons and twoneutrons in its nucleus. The two protonscorrespond to helium's atomic number two.The combined weights of protons and neu-trons in the nucleus give helium its atomicweight 4. Two electrons, held in their orbitsby the two protons, revolve around thenucleus.

27. The VOLUME of an atom is deter-mined by the orbits of its outermost revolv-ing electrons. Only a small fraction of thesize of an atom is actually occupied by theprotons, neutrons and electrons, just as thespace occupied by the sun, the earth andother planets is only a small part of oursolar system.

28. In spite of all the unoccupied SPACE,an atom is quite IMPENETRABLE toother atoms and to larger bodies. The elec-trons revolve millions of times a second,and keep everything out of the space withinquite as effectively as though they wereeverywhere at once.

29. The only things that can get insidean atom are smaller things, FRAGMENTSof other atoms, protons, neutrons or elec-trons. They must be shot with just the rightspeed. These fragments of atoms are ob-served as radiations given off by radio-active elements which are breaking upspontaneously.

30. RADIATION is wave motion, knownto us as the electro-magnetic waves usedfor radio transmission, heat, light, X-raysand cosmic rays. Large numbers of ex-tremely tiny particles in motion togetheract like waves.

31. Three types of radiation are given offby radio -active substances. ALPHA par-ticles are high-speed nuclei of helium atoms.BETA particles are high-speed electrons.GAMMA rays are electro-magnetic radia-tions similar to X-rays and light.

32. Of these, only the gamma rays areproperly called radiations, and even theseact very much like particles because oftheir short wave -length. Such a "particle"or quantum of gamma radiation is called aPHOTON.

33. In general, the gamma rays are veryPenetrating, the alpha and beta rays lessso. Even though the alpha and beta raysare not very penetrating, they have enor-mous SPEED.

34. The speed with which atom particlestravel is the source of atomic energy.ENERGY is capacity to do work. It iswork stored up for future use.

35. If you raise a weight to a heightabove the ground and suspend it there bysome device, the WORK you put into rais-ing it can be stored there indefinitely asPOTENTIAL ENERGY. It will be there,ready, whenever you decide to release it.

36. The 'energy which a moving body hasbecause it is in motion is called KINETICENERGY. The kinetic energy of any par-ticle depends upon its mass and the squareof its velocity. Energy is conserved by themoving particle until it strikes an object,then work is done.

37. All ENERGY is either potential orkinetic. Either one can be converted intothe other. These two conversions are con-tinually occurring.

38. Particles of atomic size have kineticenergy arising from several different kindsof MOTION. All atoms are constantly inmotion.

39. If the atoms are so dispersed that thematerial constituting them is a GAS, thatgas will exert pressure on all sides of thecontainer that holds it. If the container isa balloon bag, the imprisoned gas can dowork by lifting heavy weights into the air,as in the case of a dirigible.

40. Atoms which compose an element thatwill combine readily with another element,as hydrogen or carbon will combine withoxygen, have unsymmetrical arrangementsof the outer electrons in their systems.These =symmetrical arrangements tend toset up a sort of strain, which causes CHEM-ICAL COMBINATION to take place whenelements with suitable combining powersare brought together.

41. These unsymmetrical arrangementsgive rise to FORCES which result in kineticenergy. This energy appears, for example,when carbon and oxygen burn to carbondioxide, giving off heat, or hydrogen andoxygen explode to form water, again givingoff heat.

42. Chemicals combining to form stablecompounds give off energy in the process.These are known as EXOTHERMIC RE-ACTIONS. Combinations which absorb en-ergy, forming unstable compounds, areknown as ENDOTHERMIC REACTIONS.Explosives, for example, which are highlyunstable, are formed by endothermic re-actions.

43. Chemical forces, electricity and heatare all forms of energy. Potential andkinetic energy may be distinguished in eachcase.

44. These energies all arise from motionof the atom as a whole, or motion resultingfrom attractions and repulsions between theouter PLANETARY ELECTRONS of theatoms' structure.

45. Energy resulting from motion of par-ticles deep within the structure of the atomwas unknown until the discovery ofRADIOACTIVITY.

46. Radioactive elements undergo SPON-TANEOUS breaking up of their atoms, giv-ing off alpha and beta particles and gammarays. Loss of these particles causes theradio -active elements to change into otherelements.

47. The energies shown in these TRANS-FORMATIONS are thousands of timesgreater than the kinetic energies which themolecules of a gas have by reason of theirmotion when heated. They are thousandsof times greater than the energy changesper atom in chemical reactions.

48. The property of matter that connectsit with motion is INERTIA. Inertia is op-position to change of motion.

49. One conclusion that appeared early inthe development of the theory of RELA-TIVITY was that the mass due to inertiaof a moving body increases as its speedis increased.

50. This increase implied an equivalencebetween an increase in energy of motion ofa body (kinetic energy) and an Increase inits MASS.



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to position 8 for large alternating ordirect currents, or to position 9 or 10for smaller direct currents. With cur-rent flowing through one of the shuntresistors, the image of the indicatortube should overlap. Adjust the top'calibrated dial so that the image ap-pears as it did with no current flow.Read the setting and refer to theproper current chart.

Two current charts are required forposition 8 and one each for positions9 and 10. The charts can be preparedvery easily with the aid of variable a.c.and d.c. sources and accurate alternat-ing and direct current meters. Position8 has an a.c. range of 1 to .15 ampereor a d.c. range of 1 to .05 ampere.The current is limited to a maximumof 1 ampere because of the powerrating of the resistor and the largevoltage drop. Position 9 has a rangeof 20 to .5 milliamperes d.c. only; andposition 10 has a range of 1200 to50 microamperes d.c. only.

The current meter may be founduseful for approximate measurementsif no standard meter is on hand.

Resistance MeasurementsTo connect the low range ohmmeter

circuit of the test unit: Turn on thepower supply and indicator circuit, re-volve the top calibrated dial to 0 de-grees, and turn selector switch Sw4 toposition 6. Run a jumper wire from J1to J4, and connect the test prods toJ8 and J5. Short the test prods to-gether and adjust the shadow angle to0 degrees. Now connect a resistor tothe test prods and adjust the top cali-brated dial R16 until the green patternappears as it did with the prods shortedtogether. Read the number of degreesindicated and refer to the low rangeresistance chart.

The high range of the ohmmeter cir-cuit of the tester is operated as fol-lows: Rotate the top calibrated dial to0 degrees and turn selector switch Sw4to position 5. Run a jumper wire fromJ1 to J4, and connect the test prods toJ2 and J5. Adjust the uncalibrated dialso that the indicating shadow is 0 de-grees with the test prods NOT shortedtogether. Connect a resistor to the testprods, and adjust the top calibrated dialso that the shadow angle returns to 0degrees. Read the dial setting and re-fer to the high range resistance chart.

The low range of the ohmmeter cir-cuit is 400 to 500,000 ohms; the highrange is 15,000 ohms to 30 megohms.The two resistance charts can be pre-pared with the aid of a variable re-sistance and an accurate ohmmeter.

Condenser TestsTo test paper, mica, or variable con-

densers connect the jumper wire fromJ1 to J4; turn the selector switch toposition 5; plug in the test leads to J2and J5, and turn the uncalibrated knobso the shadow angle is maximum (about100°). Contact the prods to the leadsof the condenser. The shadow angle ofthe indicator tube should momentarilybe reduced as the condenser charges. If

A MULTIPURPOSE TESTER(Continued from page 13)

the shadow angle returns to normal, thecondenser is good; but if it does notreturn to normal, the condenser isshorted or leaky. If the indicator tubefails to "blink," either the condenseris open -circuited or the capacity is lessthan about .001 µf. Note that theshadow will not be defected again untilthe condenser is discharged or the leadsreversed.

Electrolytic condensers are tested ina similar manner with a few exceptions.It is necessary to connect the positiveterminal of the condenser to J2 andthe negative terminal to J5. When theprods are connected to the condenser,the shadow angle of the indicator tubeshould be decreased for several min-utes. If the condenser is good, theshadow angle will slowly increase untilit reaches a constant value. After test-ing any type of condenser, it shouldbe discharged by short-circuiting thecondenser leads. A spark can be noticedwith any condenser with a capacity of.01 pi or more.

Capacity MeterTo measure the capacity of con-

densers, revolve the top calibrated knobto 0 degrees; turn switch Sw4 to posi-tion 6, and connect the test leads to J1and J4. Adjust the uncalibrated knobso that the shadow angle of the indi-cator tube is 0 degrees with the prodsNOT short-circuited together. Connectcondenser to the prods and adjustthe top knob in order to deflect theshadow angle back to 0 degrees. Readthe number of degrees indicated by theknob and refer to the capacity meterchart.

If a stock of condensers of knowncapacity is available, the capacity meterchart can be prepared by recording thenumber of degrees rotation requiredfor each capacity. The meter has arange of .0004 to .25 microfarad.

The resourceful experimenter will be

able to think of many additional usesfor this multipurpose tester and signaltracer. The circuit does not employ anyexpensive precision parts, and makes avery interesting and useful project.

List of PartsCondensersCl, C2-16 mf 450 V. electrolytic.C3-.005 mf 600 V. tubular.C4, C17-.05 mf 600 V. tubular.C5-.02 mf 600 V. tubular.C6-25 mf 25 V. electrolytic.C7, C8, C9, C10, C13, C14, C16, C18-.03 mf

600 V. tubular.C11, C19, C20-10 mf 25 V. electrolytic.C12, C15-.0001 mf mica.

ResistorsR1, R5, R7, R14-500,000 ohm carbon.R2-550 ohm 1 w. carbon.R3-550,000 ohm volume control with switch.R4, R13, R22-100,000 ohm carbon.R6, 1124-2,000 ohm carbon.R8, 1221-1 meg. carbon.R9-10,000 ohm carbon.R10, 1212-50,000 ohm carbon.R11-250 ohm carbon.1215, R18-1 meg. potentiometers.R16-750,000 ohm volume contra'R17-250,000 ohm carbon.R19-10 meg. carbon.R20-5 meg. carbon.R23-10 ohm 10 w. power.R25-50,000 ohm carbon.

Tubes1-5Z4, 1-6F6, 1-6E8 or 6B8 -G,

1-6AF6-G, 1-6K7, 1-6H6.

Miscellaneous Parts1-Power transformer; primary 120 V. A.C.;

secondary 6.3 V. @ 3 A., 5.0 V. @ 2 A., and350-0-350 V.

1-5 inch dynamic speaker with 450 ohm fieldwinding.

1-Output transfiormer with 7000 ohm primarywinding.

5-"MIP" octal sockets.2-Tuning indicator octal sockets for 6B8 -G and

6AF6-G tubes.1-Metal tube shield for 6B8 -G tube.3-Grid caps.2-S.P.S.T. Bat -Handle toggle switches.1-S.P.D.T. Bat -Handle toggle switch.1-11 position selector switch.4-Black VA" streamlined bar knobs.3-Dial plates.1-ICA Precision Vernier Dial (4" diameter,

325°) for R15.7-Red insulated tip jacks.4 --Black insulated tip jacks.1-T-2 Tiny Neon Lamp (General Electric).1-Pilot light assembly with 6.3 V. lamp.1-Fuse and fuse mount.1-12" x 7" x 734" metal cabinet.1-Chassis.1-3 ft. 6 wire shielded cable for R.F. tube

probe.Hook-up wire, spaghetti, rubber grommets and

other hardware.

NOMOGRAM

(Continua f

PRINCIPLESroan page 25)

city and inductance. The equation is:159

f=V LC

where f is the frequency in kilocycles,L the inductance in microhenries and Cthe capacity in microfarads. This isequivalent to

159159f =

V LCWhen the scale has to be multiplied bya constant, it is simply displaced. ThusA X B = 6C can be expressed by start-ing the center scale at 6. In this case,the scale starts at 159 and ends at15,900 kc, the scale being moved down

slightly on the -actual nomogram topermit starting and ending with roundnumbers. The center line on this nomo-gram is also a division, or reciprocalscale (1/f) and runs in the oppositedirection to the other two.

References:Nomograms, Carl P. Nachord, GeneralElectric Review, May, 1944. Page 13.Nomograms - How to Make and UseThem, R. Howard Cricks, Electronicsand Television & Short -Wave World(British), November, 1940. Page 495.

Alignment Charts; Construction andUse, Maurice Kraitchik, (D. Van Nos-trand Co., New York).


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RADIOS SERVICED BY OBSERVATION(Continued from page 21)

which the receiver has been aligned. At-tempts to "align" using the high -frequency end of the dial are equallydependent on the correctness of theoscillator trimmer.-Editor)

Shortwave bands can be aligned alsoin this manner by using the govern-ment monitor station at 2.5, 5, 10 and15 megacycles to set the oscillator trim-mers, and the noise level to adjust ther.f. trimmers. Generally, the short wavebands should be aligned first.

A word or two on cut-out cases. Theseare in no way difficult. Locate thesection giving the trouble. Then con-centrate on tnat section. 21-A pair ofheadphones clipped in through a smallcondenser to the grid of the first audiotube will indicate whether the troubleis in the audio end of the receiver. Ifthe signal is still coming through thephones, connect them to the grid ofthe second audio tube, if the set hasone. If signal is also in the phones onthis stage, go back to the detector. Ifsignal is still heard, the trouble is notin the i.f. or r.f. sections of the set.

Intermittents are a more complicatedproblem but may be located often byclipping a pair of phones in at differentpoints from detector to output, andwaiting till the set stops playing, orfades to a low level. Listening to thephones will indicate whether the faultis before or after the stage in whichthey are located.

22-If a test oscillator is available,connect it to the antenna and tune inthe signal. Turn off the modulation.Turn up the volume control. Any looseconnections can easily be heard byprobing and tapping.

23-When a suspected open condenseris to be bridged with another one ona cut-out job, touch one side in theusual manner, then holding the otherlead with the forefinger and thumb,touch the other terminal with the littlefinger, thereby charging the condenserslowly through the fingers before com-pleting the connection. This will notcause sudden shock which will oftenmake an intermittent radio start operat-ing normally.

24-If the set is full of birdies, anr.f. or i.f. stage may be oscillating.This can be located best by touchingthe lead of a lead -pencil to the platelug of the tube socket. A loud clickwill be heard when you have locatedthe right one. If it proves to be an i.f.stage, everything apparently normal,put a resistor of as high a value aspossible across the primary windingof the i.f. transformer. This will stopthe oscillation. Usually 50,000 ohmswill take care of it.

Distortion is the cause of many com-plaints, so some information whichmay be of some aid in locating thetrouble, especially for the beginningserviceman, is included.

Let us go back to locating the defec-

tive section, then the defective stage,and finally the defective part. After alittle practice the serviceman will beable to distinguish by ear whether thetrouble is in the r.f., audio or speaker.However, touching the first audio tubegrid may tell the story. A rattle willindicate speaker trouble. A distortedbuzz proves the trouble is in the audio,a clear buzz indicates it is probably inthe r.f. section.

If the distortion is traced to theaudio amplifier, check all voltages care-fully, especially the bias. Be sure it iscorrect before leaving it. 25-Checkthe voltage, grid to cathode. If it isresistance -coupled you won't get muchindication of voltage, but must havesome indication on the output stage.26-The grid must have some negativevoltage. If not, check the coupling con-denser. If it is shorted or leaky thepower tube may become very hot.

27-A shorted output transformerwill cause poor tone. If it has beenreplaced with another, be sure the loadmatches the characteristics of thepower tube.

28-If you are using the usual 1000 -ohm -per -volt test meter, place yourleads from grid to ground on all stages,as the grid may be floating. This mayclear the tone. If so, replace the gridresistor. If the first audio tube is ofthe pentode type with a series screenresistor you may not read much volt-age. However, turn your voltmeterscales down. This may not increase thedeflection, but it will lower the supplyvoltage to the screen. A high voltagehere will cause distortion.

If the distortion trouble has shownup since you have been working on theset, you have probably caused it your-self. Check over the work you havedone for defective parts, poor solderingor wrong connections.

R.f. distortion may be due to mis-alignment or to the wrong bias voltage.Check for both.

If distortion is only on strong signals,disconnect the antenna. If this clearsup distortion you can be sure it is dueto wrong bias voltage. On the oldersets using 24's, etc., voltage under 25volts on the screen or over 12 volts onthe grid will cause the tube to be un-stable. It will be necessary to installsuper -control tubes or a local -distanceswitch to lessen pickup.

Again check the tubes as to theirright positions in sockets. A sharp cut-off type like the 6J7 will not replace asuper -control tube of the 6K7 type,where the volume is controlled by theC -bias either manually or with auto-matic volume control, which includesalmost all sets in use today.

Be thorough. Don't skip a stage untilyou have checked everything. Partic-ularly, don't take it for granted thatthe tubes are in the right places, eventhough you may have replaced them inthe sockets yourself. Check them again!


TABLE OF REACTANCESInductive Reactance

INDUCTANCE

IN HENRIES

APPROXIMATE REACTANCE IN OHMS

1000 C.P.S. 400 C.P.S. 60 C.P.S:

I h 6250 ohms 2500 ohms 375 ohms

2 h 12500 ohms 5100 ohms 750 ohms

5 h 31250 ohms 12550 ohms 1900 ohms

10 h 63000 ohms 25000 ohms 3800 ohms

20 h 125000 ohms 50000 ohms 7500 ohms

30 h 190000 ohms 75000 ohms 12000 ohms

40 h 250000 ohms 100000 ohms 15000 ohms

50 h 310000 ohms 125000 ohms 19000 ohms

60 h 380000 ohms 150000 ohms 23000 ohms

70 h 440000 ohms 175000 ohms 27000 ohms

80 h 500000 ohms 200000 ohms 30000 ohms

90 h 570000 ohms 225000 ohms 34000 ohms

100 h 625000 ohms 250000 ohms_

38000 ohms

Capacitive Reactance

CAPACITYIN

MICROFARADS

APPROXIMATE REACTANCE IN OHMS

1000 C.P.S. 400 C.P.S. 60 C.P.S.

.001 MF

.005 MF

.01 MF

.02 MF

.05 MF

.1 MF

.5 MF

1.0 MF

5.0 MF

10.0 MF

160000 ohms

32500 ohms

16000 ohms

8000 ohms

3250 ohms

1600 ohms

325 ohms

160 ohms

32 ohms

16 ohms

400000 ohms

72000 ohms

ohms

20000 ohms

8000 ohms

4000 ohms

800 ohms

400 ohms

76 ohms

40 ohms

3000000 ohms

520000 ohms

265000 ohms

132600 ohms

53000 ohms

26000 ohms

5500 ohms

2700 ohms

530 ohms

250 ohms

Complete Ohm's Law FormulasVoltage in Volts Current in Ma Resistance in Ohms Power in Watts

KNOWN KNOWN1000 X Volts Volts X Ma

Ma 1000

KNOWN1000 X Volts KNOWN Volts X Volts

Ohms Ohms

KNOWN1000 X Watts Volts X Volts KNOWN

Volts Watts

Ma X Ohm% KNOWN KNOWN Ma X Ma X Ohms1000 1,000,000

1000 X Watts KNOWN1,000,000 X Wafts

KNOWNMa Ma X Ma

KNOWN KNOWNV Ohms X Watts 74711000Ohms _

According to Ohm's Law, if two of the three quantities, resistance, voltageor current, are known, the other can be calculated. The power consumed in thecircuit can also be computed from these two quantities. The chart above givesat a glance the formula to use when any two of either volts, milliamperes,ohms or watts are known, to find the other two. Since radiomen are usuallyinterested in milliamperes, current is so expressed rather than in the traditionalamperes.

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1947 RADIO -ELECTRONICS REFERENCE ANNUAL35

ADIO. Rhil

RADIO -CRAFTLIBRARY SERIES

10 New BooksEach of the books in this new series is crammed full of meatymodern material for immediate, practical application. The booksare all set in modern easy -to -read type, carefully printed and wellillustrated. Price 50c each, postpaid.

No. 29HANDY KINKS AND SHORT CUTS. A compilation of practical expedients andmethods of overcoming difficulties encountered by every radio man, suggested byreaders of RADIO -CRAFT. Here are kinks on antennas, kinks on servicing, kinks forthe shop, kinks on power supplies, etc.-arranged by sections for easy reference,and illustrated.

No. 30UNUSUAL PATENTED CIRCUITS 1944-1946. A digest of electronic patents,many the result of wartime research, valuable both to the experimenter and to anyonein the electronic field. Divided into five sections: Control Circuits; Power Supplies;Detectors and Amplifiers; Miscellaneous and Foreign Patents. Simplified circuitdiagrams illustrate the text.

No. 31RADIO QUESTIONS AND ANSWERS. Here are the answers to questions mostfrequently asked of the "Question Box" editor of RADIO -CRAFT. The materialselected is well diversified and chosen for practical application to workaday problems.Circuit diagrams are supplied with the answers. Not ready until Feb., 1947.

No. 32ADVANCED SERVICE TECHNIQUE. An up-to-date collection of informationon specialized phases of servicing, appealing definitely to the advanced servicemanrather than the beginner. This book is not intended as a course in advanced servicing,but strictly a diversified library of ideas, methods, and procedures not likely to befound in other textbooks designed for the professional serviceman.

No. 33AMPLIFIER BUILDER'S GUIDE. A valuable book for the designer and con-structor of sound equipment. Theory and construction of audio amplifiers are trezttedin separate parts. The theory section while not intended as a complete treatise on thesubject contains an unusually wide range of technical data on amplifier design. Thisis followed up by good solid information on the construction of a variety of audioamplifiers with power outputs from 8 to 30 watts. Not ready until Jan., 1947.


RADIO -CRAFTLIBRARY SERIES

50c EachNo. 34

RADIO -ELECTRONIC CIRCUITS. Here is an extensive collection of circuitdiagrams with a brief description of each, to serve as a source of inspiration to theexperimenter bent on developing further new circuits. Constructional data is purposelylimited to allow space for a maximum number of circuits. Not ready until Feb.,1947.

No. 35AMATEUR RADIO BUILDER'S GUIDE. Here is a book for the "ham" whobuilds his own. Practical, down-to-earth, and devoid of all radio theory, it consistsentirely of "How to Build" articles. It is divided into three sections: 1. Receivers2. Transmitters. 3. Miscellaneous (antennas, converters, and other equipment). Thebook is packed with usable material from cover to cover. Not ready until Feb.,1947.

No. 36RADIO TEST INSTRUMENTS. Every radio man can use this latest book on build-ing test equipment. The book places more emphasis on the practical side of construct-ing testers than on classroom theories. Among the instruments described are signaltracers, capacity meters, portable and bench multicheckers, signal generators, tubecheckers and electronic voltmeters.

No. 37ELEMENTARY RADIO SERVICING. A book for the radio man who knows littleabout radio repair. It shows how to get started and keep going. A wide range ofessentials is covered in logical sequence: Planning and Equipping the Shop, Syste-matic Circuit Checks, Signal Tracing Methods, Servicing Midget Receivers and otherfundamental servicing topics. Not ready until Jan., 1947.

No. 38HOW TO BUILD RADIO RECEIVERS. Here is a book for the set builder. 18modern receivers are described-a sufficient variety to appeal to practically everyradio fan. The selection includes the following types: Short-wave, broadcast, v. h. f.,portable, a.c.-operated, a.c.-d.c. and miniature. Complete coil winding informationis given where necessary.

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1947 RADIO ELECTRONICS REFERENCE ANNUAL 37

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RADIO HEARING AID

(Continued front page 15)

the plate section of the oscillator coilis short-circuited and therefore the first1R5 does not convert any frequency orproduce any i.f. The 1S5 therefore am-plifies at a.f. only. The amplified a.f.appears across the 1-meg resistor lo-cated after the primary of the i.f. coiland is applied through an .001-Af con-denser to the third grid of the second1R5. The second 1R5 is used as anaudio -frequency mixer.

The Switch PositionsThe fact that the secondary of the

first coil is in the input circuit of the1S5 and that the primary of the sec-ond i.f. coil is in the output of the sametube does not impair the performanceat a.f. The reactance and mutual induc-tance of the i.f. coils is infinitesimal atlow frequencies. In position 1 the ap-paratus works as a hearing aid wherethe 1S5, the second 1R5 and 1S4 all am-plify at a.f.

In position 2 the oscillator coil works.The i.f. is applied to the input of the1S5. In the output, the second i.f. coilapplies the i.f. to the diode section ofthe same tube. The output is fed to thefirst grid of the second 1R5. The two50 -µpi condensers in the input and out-put of the 1S5 close the i.f. path toground. The microphone is still con-nected and its output is amplifiedas when switch is in position 1.In this case the 1S5 amplifies ati.f. (radio) and a.f. (microphone).The i.f. signals are also demodulatedby the diode section of the 185. In thisposition the apparatus works as radioand hearing aid.

In position 3, the microphone is dis-

Threshold of Audibility

connected. The 1S5 amplifies only i.f.(and demodulates). This is the "radioonly" position.

The second 1R5 is an audio -frequencymixer. The a.f. rectified by the diode isapplied to, grid 1, a.f. amplified by the1S5 to grid 3. In the plate circuit of thesecond 1R5 we find both signals in am-plified form when grids 1 and 3 are bothoperating. We find only one signal wheneither grid 1 or grid 3 is working alone.

No definite assembly sketch can begiven since the location of the com-ponent parts depends too much on theirphysical shape. The photographs showpositions of the parts in the receiverdescribed.

The sensitivity of the radio receiveris better than 400 microvolts r.f. input(broadcast band) for 50 milliwatts a.f.output.

DECIBEL ACOUSTICSCALE

Levl of Sound Decibels,r)

Low Whisper 10Suburban Garden 20Average Home 39Average Office 40Motor Car 50Brisk Conversation 60Motor Truck 70Loud Radio Music 80Pneumatic Drill 90Boiler Shop 100Unsilenced Airplane Engine 110Loud Thunder 120Threshold of Pain 130

SCALE OF PREFERRED NUMBERSUse of the preferred number system

will become increasingly common inevaluating certain radio parts. In theold system steps were only apparentlyuniform. For example, resistors werenumbered in "uniform" steps of 100,with the result that the 200 -ohm was100 per cent greater than the 100 -ohmresistor, while the 1000 -ohm was only10 per cent greater than the 900 -ohmresistor.

In the preferred number system, eachstep increases over the last by the sameamount, subject to slight variations to"round off" the values. Thus, beginningwith 100 ohms, resistors increase insteps of approximately 20 per cent to120, 150, 180 and 220 ohms. There isno resistance value in this scale be-tween 820 and 1000 ohms. (See table).

Distance between the steps is gov-erned by the tolerance of the com-ponent. A 150 -ohm resistor of 10 percent tolerance may have any valuebetween 150 plus 10 per cent and 150minus 10 per cent, or between 135 and165 ohms. The upper limit of a 120 -ohm

and the lower limit of a 180 -ohm re-sistor are 135 and 162 ohms respec-tively. Thus steps of approximately 20per cent are sufficient to assign valuesto all resistors in this series and anyvalues between those would be mean-ingless. For units of 5 per cent toler-ance, the values would increase inapproximately 10 per cent steps, asshown in the table.

In the table on the next page, thefirst column shows the preferred valuesfor resistors of 20 per cent tolerance,the second for 10 per cent and the thirdfor 5 per cent resistors. The fourthcolumn shows the older standardvalues. Note that with only sixteen re-sistors, the whole range between 50and 1,000 ohms (taken as an example)can be covered with differences of ap-proximately 20 per cent, while with theold standard, fourteen were used tocover the same range with a muchgreater proportional difference betweenmany of the values, which follow eachother irregularly and illogically.

The preferred number system willcome into more general use not only in


the case of resistors, but condensers andvery likely chokes and other com-ponents will increasingly adopt themore efficient method. As it is funda-mentally a system of numbers, it canbe applied to any case where units are

required, and is being discussed in themechanical trades and the engineeringprofession. It is therefore well worththe reader's while to familiarize him-self with the units, as he is likely tomeet them with increasing frequency.

Preferred Values of ResistanceOld

StandardResistance

Values

Preferred Values of Resistance OldValues

Standard±20% ±10% ±5% ±20% ±10% ±5%

50 25,00051 27,000 27,000

56 56 30,000 30,00062 33,000 33,000 33,000

68 68 68 36,00075 75 39,000 39,000

82 82 40,00091 43,000

100 100 100 100 47,000 47,000 47,000110 50,000

120 120 51,000130 56,000 56,000

150 150 150 150 60,000160 62,000

180 180 68,000 68,000 68,000200 200 75,000 75,000

220 220 220 82,000 82,000240 91,000

250 100,000 100,000 100,000 100,000

270 270 110,000300 300 120,000 120,000 120,000

330 330 330 130,000350 150,000 150,000 150,000 150,000

360 160.000390 390 180,000 180,000

400 200,000 200,000

430 220,000 220,000 220,000450 240,000

470 470 470 250,000500 270,000 270,000

510 300,000 300,000560 560 330,000 330,000 330.000

600 360,000620 390,000 390,000

680 680 680 400,000750 750 430.000

820 820 470,000 470,000 470,000910 500,000

1000 1000 1000 1000 510,0001100 560,000 560,000

1200 1200 1200 600,0001300 620.000

1500 1500 1500 1500 680,000 680,000 680.0001600 750.000 750,000

1800 1800 820,000 820.0002000 2000 910.000

2200 2200 2200 1.0 Meg. 1.0 Meg. 1.0 Meg. 1.0 Meg.2400 1.1 Meg.

2500 1.2 Meg. 1.2 Meg.2700 2700 1.3 Meg.

3000, 3000 1.5 Meg. 1.5 Meg. 1.5 Meg. 1.5 Meg.3300 3300 3300 1.6 Meg.

3500 1.8 Meg. 1.8 Meg.3600 2.0 Meg. 2.0 Meg.

3900 3900, 2.2 Meg. 2.2 Meg. 2.2 Meg.4000 2.4 Meg.

4300 2.7 Meg. 2.7 Meg.4700 4700 4700 3.0 Meg. 3.0 Meg.

5000 3.3 Meg. 3.3 Meg. 3.3 Meg.5100 3.6 Meg.

5600 5600 3.9 Meg. 3.9 Meg.6200 4.0 Meg.

6800 6800 6800 4.3 Meg.7500 7500 4.7 Meg. 4.7 Meg. 4.7 Meg.

8200 8200 5.0 Meg.9100 5.1 Meg.

10,000 10,000 10,000 10,000 5.6 Meg. 5.6 Meg.11,000 6.0 Meg.

12,000 12,000 12,000 6.2 Meg.13,000 6.8 Meg. 6.8 Meg. 6.8 Meg.

15,000 15,000 15,000 15,000 7.0 Meg.16,000 7.5 Meg.

18,000 18,000 3.0 Meg.20,000 20,000 8.2 Meg. 8.2 Meg.

22,000 22,000 22,000 9.0 Meg.24,000 9.1 Meg.

10 Meg. 10 Meg. ID Meg. 1° Meg.

set.

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PHONO AMP. KITWith 3 tubes and 5, speaker, 7.95less tubes or speaker 5 95

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AMPLIFIER AND RADIO TUNER(Continued from page 14)

An octode or pentode converter isused in the first stage of a superhetero-dyne tuner. The superhet was used be-cause of space limitation, in this case.Standard broadcast r.f. oscillator andi.f. coils are used with a 365-p,g, two -gang variable condenser. Noticeable isthe .0004-pf mica condenser in serieswith the oscillator coil primary andground, to assure more uniform bandspread. The i.f. signal is amplified at456 kc, through a 7A7, then detectedby a double -diode triode 7C6. One ofthe diodes is used to supply a.v.c. voltageto the first stage. The radio volumecontrol doubles as diode load. The a.f.signal from the triode plate of the 7C6

is coupled through a condenser andd.p.d.t. switch on back of the tunervolume control, to the 7C7 controlgrid. One half of the radio volumecontrol switch controls a pilot lightused to denote whether the tuner is inor out of the a.f. circuit.

Incorporated is a well filtered full -wave power supply, good for 300 voltsat 150 milliamperes -the actual high -voltage current drain being about 115ma.

A complex power switch is used inorder to control the phono motor,mounted on top of the cabinet. By mov-ing the power switch arm one pointfrom the "off" position, power is ap-

CONVERSION RATIOS

MULTIPLY BY

Amperes 1,000,000,000,000Amperes 1,000,000Amperes 1,000Cycles .000,001Cycles .001Farads 1,000,000,000,000Farads 1,000,000Farads 1,000Henries 1,000,000Henries 1,000Horsepower .7457Horsepower 745.7Kilocycles 1,000Kilovolts 1,000Kilowatts 1,000Kilowatts 1.341Megacycles 1,000,000Mhos 1,000,000Mhos 1,000Microamperes .000,001Microfarads .000,001Microhenries .000,001Micromhos .000,001Micro -ohms .000,001Microvolts .000,001Microwatts .000,001Micromicrofarads .000,000,000,001Micromicro-ohms .000,000,000,001Milliamperes .001Millihenries .001Millimhos .001Milliohms .001Millivolts .001Milliwatts .001Ohms 1,000,000,000,000Ohms 1,000,000Ohms 1,000Volts 1,000,000Volts 1,000Watts 1,000,000Watts 1,000Watts .001Diam. Circle 3.1416Diam. Circle .886Inches 2.54

TO OBTAIN

MicromicroamperesMicroamperesMilliamperesMegacyclesKilocyclesMicromicrofaradsMicrofaradsMillifaradsMicrohenriesMillihenriesKilowattsWattsCyclesVoltsWattsHorsepowerCyclesMicromhosMillimhosAmperesFaradsHenriesMhosOhmsVoltsWattsFaradsOhmsAmperesHenriesMhosOhmsVoltsWattsMicromicro-ohmsMicro -ohmsMilliohmsMicrovoltsMillivoltsMicrowattsMilliwattsKilowattsCircumference CircleSide Equal SquareCentimeters

To get units in first column, reverse the process. For example, to get inches,divide centimeters by 2.54.

MaterialAirBakeliteCelluloidEboniteElectrical fiberFormicaGlass (windowGlass (electrical)LuciteMicaPaperNylonParaffin waxPolystyrenePorcelainQuartzShellacSteatite (commercial)Steatite (low -loss)Varnished clothWood (dry)

plied only to the amplifier and tuner;by moving a step further, the arm ap-

The complete equipment requires little space.

plies power also to the phono motor.A third section of the power switchapplies 6.3 volts to a pilot indicator.

The Superamp is a practical and com-pact unit, and the added radio tunerhas been found a very useful auxiliaryto the PA system on many occasions.

INSULATING MATERIALS(At 1 megacycle frequency)

Power DielectricFactor Constant

1

4.54.52.85

4.88

4.52.65-82.53.62.252.57

3.83.56

6

2.52-7

1.450.55

1.1

1.40.51.5

0.2variable

2.20.I

.020.7

.020.1

0.20.2*3

4

*Low -loss steatite has a power factor of ap-proximately 0.2 percent up to 100 megacycles,while that of commercial grades increaseswith frequency.

SIZE OF TRANSFORMER COREFOR OUTPUT WATTAGE

Volt -ampsOutput

Core size(Sq. In.)

25 1.050 1.575 1.75

100 2.0150 2.5200 3.0250 3.5350 3.75500 4.0

These sizes are generously calculatedand allow ample regulation.

The number of primary turns in atransformer is calculated from theformula: N=7.5 x E. Thus a core whosecross-section is one square inch wouldrequire a primary of about 850 turn=,on 115 volts (N=7.5 x 115)

1


A VIBRATOR AMPLIFIER(Continued from page 8)

ployed, the secondary winding being intwo sections to provide as completecoupling as possible.

The entire amplifier and power packwere assembled on a metal chassis 9

inches long by 51/2 inches from frontto back. A front panel 10 inches by 7inches was cut from a scrap piece ofmasonite. This carried the controls,terminals, input and output sockets(these were standard wafer -type tubesockets).

10" INSIDE

Fig. 2-A front view of the speaker cabinet.

Although the speaker seems housedin a bass -reflex baffle (Fig. 2) there'sreally not very much bass about it,although music from records soundsquite well-balanced. The speaker boxhas a volume of 490 cubic inches andwith the two vents - one each side ofhe speaker - the "bass" resonant fre-

quency is about 200 cycles per second,while the natural diaphragm resonanceof the speaker is about 150 cycles persecond.

The speaker has a 20 -ounce Alnicomagnet, a voice coil diameter of ap-proximately 1 inch, a very light dia-phragm and more than averageefficiency. This speaker was chosenbecause it was the largest speaker (ofreasonable efficiency) that would fit inthe box.

Type of MicrophoneIt is very undesirable to produce

extra distortion from inter -modulationin the first stage (before the unwantedfrequencies are attenuated), so themicrophone chosen was of the crystaldiaphragm type and was worked intoa rather low resistance load (250,000ohms). Suitable types are the D104Astatic, the 707A Shure and the VT73Turner. (This last was-I believe-suc-ceeded by a much better type a numberof years ago.) Recently some dynamicmicrophones were tried and provedquite satisfactory.

On one occasion when a large am-plifier broke down, this little job wasconnected to a pair of Long -horn speak-ers and used for street advertising. Apair of speakers in parallel gave a loadof 5 ohms instead of the usual 3 ohmsbut this did not seem to matter, andthe work was carried on successfully.

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ALL -BAND OSCILLATOR

(Continued from page 18)

equals 150. All i.f. bands can be cali-brated this way.

This process should be repeated for(at least) each five degrees of the dialfrom 100° to 0°. The results are re-corded on a graph. The vertical linesrepresent the number of degrees, andthe horizontal lines the frequency.When sufficient points have beenmarked on the chart, a curved line canbe drawn through all the points. Thiswill make it possible to set the oscilla-tor to any desired frequency within therange of the coil and condenser.

The broadcast band can be calibratedeasily. Tune the receiver to a stationwhich operates on a known frequency.Then tune the oscillator so that it gen-erates a signal on the same frequency.Record the various frequencies takenfrom known stations on a chart as wasdone with the other coils in the set.

The short-wave coils can be calibratedwith the aid of harmonics. Set the os-cillator to precisely 1000 kilocycles.Then tune in the first harmonic (2000kc) on the short-wave range of thereceiver. Remove the broadcast signalgenerator coil and insert a short-wavecoil which will generate a signal thatcan be received without touching thetuner of the receiver. The oscillatorshould then be operating at 2 mega-

cycles, the same frequency as the har-monic originally received. Record thisfrequency on a chart, and repeat thisprocess using another harmonic. Theharmonics from the oscillator, whentuned to 1000 kilocycles, will fall on 2,3, 4, 5, 6, 7, 8, 9, 10, etc., megacycles.

R.f. stages, i.f. stages, and superhet-erodyne oscillators can be alignedthrough the use of the test oscillatorand an output meter. The aerial andground leads are disconnected from thereceiver. A lead from the black outputjack is connected to the ground postor directly to the chassis. A lead fromthe red output jack should be connectedto the aerial post. In this test the redjack lead should be shielded, to reduceinterference from local broadcast sta-tions. An output meter should be conknetted to the output stage so that thereceiver can be accurately aligned bythe visual method.

The r.f. oscillator is very useful forcalibrating radio equipment. The a.f.oscillator may be used for testing a.f.equipment.

Automatic volume control circuits canbe tested by comparing the output read-ing of the receiver with different a.v.c.tubes. A decrease in reading with anew tube shows that the old one isdefective.

The selectivity of tuned circuits canbe determined by noting the outputreading when the frequency of the oscil-lator is changed a few degrees on eitherside of the point of resonance.

The frequency of resonance of a coiland condenser can be determined byopening the lid of the signal generatorand placing the coil to be tested nearthe oscillating coil. A voltmeter shouldbe connected to the meter jacks. Whenthe oscillator is tuned to the frequencyof the coil and condenser combination,a current will be induced into the coil.This will cause an increase in the oscil-lator plate current which will be indi-cated on the voltmeter.

The largest output from the r.f. os-cillator can be obtained by connectingone lead to the chassis and the otherthrough a small condenser (.0001 uf)to the "G" connection of the coil. Atlow radio frequencies the output will besufficient to cause a small neon lampto glow and to be visible on the screenof an oscilloscope. This connection isnot used for ordinary tests becausethe oscillator would lack stability andselectivity.

Parts ListCondensersCl, C2-20-20 mf 150 v. electrolytic condenserC3-320 mf variable condenserC4-3-30 mf low -loss trimmer condenserC5-.0001 mf mica condenserC6-.5 uf 600 v. tubular condenserC7, C8, C11, C15-.06 mf 600 v. tubular condensersC9-Two insulated wires twisted togetherC10-.002 mf 600 v. tubular condenserC13-.005 mf 600 v. tubular condenserC16-.05 mf 600 v. tubular condenser

ResistorsR1-250 ohm 10 watt wire -wound power resistorR2-250 ohm 25 watt wire -wound power resistorR3 -10u0 ohm 2 watt carbon resistorR4-50,000 ohm carbon resistorR5-100,000 ohm potentiometer with switchR6-10,000 ohm carbon resistorR7-250,000 ohm carbon resistorR8-500,000 ohm carbon resistorR9-1 meg. or higher resistance potentiometer

with switchR10-500,000 ohm potentiometer with switch

Tubes1-6J7 radio tube1 -6C8 -G radio tube1-35Z5-GT radio tube

Miscellaneous Parts1-Audio transformer (secondary not used)

plate coupling choke, (T1)2-S.P.D.T. Bat -Handle toggle switches1-ICA precision vernier dial 4 inch diameter

(No. 2169)3-Black pointer knobs1-Deluxe 0-10 dial plate for R9

tip jacks3-Red large diameter molded Bakelite insulated

tip jacks3-Black large diameter molded Bakelite in-

sulated tip jacks1-2.5 mh. r.f. choke3-"MIP" octal sockets1-Am phenol 5 -prong socket2-grid caps for 6J7 radio tube and 6C8 -G radio

tube9 -5 -prong 114" dia., 21/i" high Bakelite coil

forms1-TA" red jewelled bracket with miniature base1-Number 40 pilot lamp1-Power cord with plug1-Red test prod with alligator clip1-Black test prod with alligator clip1-Shielded cable with alligator clip1-Penlight cell (size AA)1-8" x 4%" x 11/2" metal chassis1-10" x 6" x 7" metal chassis with ventilation

louvres on sides and hinged top2-Mounting strips25 ft. hook-up wire, coil wire, rubber grommets,

hardware, etcThe plug-in coil chart is self-explan-

atory, all information being given.

or


A THREE -CHANNEL AMPLIFIER(Continued from page 11)

time restoring the musical equilibrium.To establish the response curve of

which we have just spoken, it is neces-sary to know that of the ear. Thatcurve has been traced by the physi-cians and physiologists, who have es-tablished it by the average of severalthousands of individual cases.

Since the amplifier is destined forthe pleasure of one sole listener, itmay well happen that the particularear in question will be very differentfrom the "average ear." Therelore itis infinitely preferable to permit theuser to adapt the amplifier response tohis own needs and tastes.

With this idea the amplifier heredescribed was conceived. It has threechannels, one for each band of fre-quencies: bass, medium and high, theamplifier for each channel being con-trollable independently of the others.

Design and ConstructionWe shall scrupulously avoid the hack-

neyed description of "the tube A, plateof which is coupled to the grid of tubeB through the blocking condenser C,etc.," refusing to consider the readerso benighted that it is necessary topoint out that which he can see clearly

in the accompanying schematic draw-ing. On the other hand, we will devotemore time and details to the interest-ing and unusual features.

The 1-megohm resistors R1 and R2isolate the three inputs from eachother, preventing a mutual short-cir-cuit. The condenser Cl has as its objectthe short-circuiting of the high andmedium notes for its particular input.Therefore the 6F5 stage at the top ofthe schematic is the "boss" pre -ampli-fier. Its gain is regulated by the volumecontrol P1. The condenser C2 preventsbasses from reaching the grid of the6F5 directly below the "bass" input.Therefore, only mediums and highspass. But, as we shall see, the highswill be attenuated further on. Thisstage constitutes therefore the "me-dium" pre -amplifier, controlled by P2.

The output of these two stages isapplied, through a common volumecontrol P4, a 6C5 and a transformer,to a push-pull stage, using 6A5 triodes.Their low internal resistance permitsexcellent reproduction of the basses.The negative feedback circuit R4, C4weakens the high notes, the condensersC4 being of low value (50 lag). Theoutput transformer has two windings,the higher potential one being tapped

to permit adaption to loudspeakers ofdifferent impedances. This arrangement-two 6F5's, 6C5 and two 6A5's-con-stitute the bass and medium amplifier.

The low -capacity condenser C3 (25p.p,f) permits only the highs to pass.To enhance this effect the cathode cir-cuit of the 6J7 is decoupled with a con-denser of only 0.1 pf (across 800 ohms)which reduces the bass and mediumnotes through degeneration.

This stage constitutes the "high"pre -amplifier. Its gain is also inde-pendently controllable, by volume con-trol P3. It is followed by a 6F5 and6F6.

The output transformer feeds aspeaker of a small diameter, intendedonly for the reproduction of the highs.Under such conditions, this speaker hasa marked directional effect. To softenthis effect, signals of lower frequenciesmay be fed (at low level) into the"high" amplifier. This has been donethrough use of the resistor R.

Note also the milliammeter whichpermits rapid comparison of the platecurrents of the 6A5's, or measurementof the total plate current of' the two;a feature which facilitates balancingthe push-pull stages and also gives acheck on the condition of the apparatus.

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RADIO LABORATORY IN PORTABLE UNIT(Continued from page 19)

stability with respect to load, becausethe only coupling between the oscilla-ting circuit and the load is the electronstream flowing through the other ele-ments to the plate. The plate is electro-statically shielded from the oscillatingportion by the screen, which is at r.f.ground potential. It is also stable inrespect to voltage variations. Anyvariable condenser which was or couldbe used to cover the broadcast bandwith standard coils may be used here.Standard 4 -prong plug-in coil formsare used. The coil is wound continuouslybut is tapped for the cathode connec-tion. Complete information on coil datais given in the table. The 6SK7 is a

Coil Table(All coils are wound on 11/2 in. forms)

I.F. coil (456 kilocycle) No. 26 enamelwire. 170 turns close wound; cathode tap50 turns from ground.

Broadcast-No. 22 d.c.c. 100 turns closewound; cathode tap 13 turns fromground.

30 Meter-No. 22 d.c.c. 29 turns closewound; tap 2 turns from ground.

40 Meter-No. 22 d.c.c. 16 turns spaced134 inch; tap 11/2 inch from ground.

20 Meter-No. 22 d.c.c. 7 turns spaced11/2 inch; tap 11/2 turn from ground.

perfect tube for the job; being singleended, wiring is easy, and one can beassured of complete shielding. Gridcondenser and grid leak should be ofthe smallest physical size procurableand should be fitted with a metalshield. The value of the resistor supply-ing voltage to the potentiometer isgiven as 50,000. Actually it should bedetermined after the voltage from thepower -pack is known. For the 6SK7 thevoltage at X should be 100 volts, whichis the screen voltage given in the tubemanual. B -plus and filament voltagesare supplied from the power -pack be-low by two wires plugging into themale receptacle situated at the backof the panel.

As an r.f. and i.f. signal -tracing unitthe tester compares not unfavorablywith elaborate 3 -stage TRF analysts.For signal tracing the output jack isconnected to the input of the audiochannel by a short connection. Signalscan then be picked up with a shieldedtest probe.

A word of warning is needed foranyone who thinks that all that isnecessary is to pick out the right sizedcondensers and stick them together.There is a world of difference betweenan ordinary regenerative set and onethat is carefully designed. When usedas a service tool one wants no worriesas to whether that birdie, whistle, humor howl is coming from the defectiveradio or from one's test instrument.Here are a few pointers: 1.-Plate andgrid wires must be very short, yetparts must not be crowded. 2.-Halfthe battle is in constructing strong,neat shields. 3.-Build rigidly andsolder carefully. 4.-Three factors in-

fluence. the smoothness of going intoand out of oscillation; the amount offeedback, grid leak, and antenna coup-ling. The final setting of the cathodetap on a coil should be such that thedetector breaks into oscillation at therecommended screen grid value as givenin the tube manual. If it oscillates onlyat a higher voltage too little feedbackis present and the cathode tap shouldbe moved higher on the coil. A lowenough value of feedback should beused to ensure smooth regenerationfrom an almost noiseless condition toslight hiss, loud hiss, whistle (whenpassing station). If it comes into oscilla-tion with a plop and is not stable(starts squealing if you shake yourfist in its face) adjustment of the grid-leak or antenna coupling is indicated.If, however, smooth regeneration can-not be obtained with at least a one-megohm leak, the antenna couplingshould be loosened; that is, use asmaller condenser. A tiny trimmer con-denser works well in this position.

5.-Another disease from which re-generative sets suffer is fringe howl,noticed when tuning through a station.This is more than a matter of toomuch regeneration. It means that r.f.signal is getting through into the audiosection. The remedy lies in better r.f.filtering.

6.-A good regenerative set shouldhave little or no hum. Methods ofelimination are: 1.-More careful shield-ing, not just of wires but of partsand sections. 2.-Grounding of chassis.3.-Better power supply. 4.-Groundone side of heaters and by-pass otherside through an .01 itf condenser.

To obtain an audio signal for testpurposes, plug in broadcast coil, attachantenna to input jack (a small built-inantenna in the top of the cabinet bringsin all local stations). Connect outputjack to input of audio channel. Tunein a station.

Modulated B.F. or I.F. SignalAs anyone who was ever bothered

by interference from a neighbor's radioin the old days knows, a regenerativeset can be made to give out a self -modulated r.f. signal. This is done byturning up the regeneration controluntil the tube breaks into audio oscilla-tion. If the tube merely oscillatessmoothly the result is an unmodulatedsignal. If the regeneration is increasedstill more the grid becomes more nega-tive until the plate current has beenreduced to so low a level that the tubestops oscillating. The grid then be-comes less negative and oscillationscan again begin, so an audio cycle isrepeated and is superimposed upon thefundamental r.f. wave.

It is unnecessary to tell how one usesan r.f. or i.f. signal in locating a faultin a radio. Nor is it necessary to out -


line the alternative method of signaltracing. It hardly needs to be men-tioned that when the test instrument isused for signal tracing the apparatusis not used in an oscillating condition.The regeneration control is merely ad-vanced to a position where the appara-tus is sufficiently sensitive to pick upa signal, detect and amplify it andpass it on to be registered by the audiochannel. Always use a shielded testprobe when picking up an r.f. or i.f.signal from a radio.

Diode Vacuum -Tube VoltmeterTo use, the d.c. pocket voltmeter,

seen at the right in the photo, is con-nected to the Diode Rectifier. Refer tothe circuit diagram for connections andnote that the two ground terminals onthe lower part of the panel are usedalong with the two pin jacks in theupper left corner. This circuit readspeak a.c. volts and while it is not assensitive as more complicated v.t.v.m's.it is a distinct improvement over or-dinary a.c. voltmeters. The RMS valueof the a.c. voltage under measurementcan be determined by multiplying thepeak value as read on the meter by0.71. Most common measurements arepeak voltages across filter condensers;to check turns ratios of transformers,and as an audio -frequency output meteracross the voice coil of a speaker. Thecondenser must be a high quality paper2.0 p.f. It should be noted that thiscircuit has certain limitations. It is nomore sensitive than the meter withwhich it is used and loads the circuit.As here constructed it has too high

losses to measure r.f. frequencies.Many possible uses occur to one who

has an idle evening with the apparatus.The audio -amplifier becomes a recordplayer, a music booster or a miniaturePA system. The broadcast band may becovered, and short-wave coils can easilybe wound for foreign reception.

You can also try modulating thesuppressor -grid of the 6SK7 with astrong audio signal from a record play-er or a carbon microphone. The broad-cast can be picked up by the kitchenradio. (But not by the neighbor's radioor the federal authorities won't like it.)

A DECIBEL NOMOGRAM(Continued from page 27)

5-Another useful transformation isthat of percentage to decibel loss. Am-plifiers are sometimes rated in per-centage distortion or noise and some-times in db down from the rated output.Only two variables are concerned, per-centage and decibels. To operate, theruler is kept fixed against the bottomindication of the left-hand scale at alltimes. Percentage is read at E, whiledb down is read at D. A particularamplifier is known to have 2 per centdistortion. How many db down is this ?Placing one end of the ruler at 100volts at the bottom of scale B and theother end at 2 volts (2%) on E, weread -34 db on D. But since we aredealing with power rather than voltage,this reading must be divided by two.The result: --17 db. Distortion is 17db below output power level.

DYNAMIC HANDFUL


and the tracer have a common ground.When testing an a.c.-d.c. set that

uses a common positive on the filterblock, connect prod C first to one nega-tive of the condenser, use only the onethat gives the least amount of hum.

When testing the first r.f. or de-tector stage of a loop -operated set, anexternal antenna will be required onthe set.

There is no danger of a short circuitbecause of the blocking condenser.There is no danger of an electric shockbecause of the wooden cabinet insula-ting the chassis.

The short test prod is covered witha piece of spaghetti except the verytip, to prevent accidental shorts withthe prod itself.

The cabinet was constructed fromthin walnut panelwood, but if the ser-viceman should desire he can build thecabinet out of plywood.

Connections to phone jacks A B Care made after tracer is mounted intothe cabinet.

The grid leads on the first tube shouldbe made as short as possible to pre-vent hum.

When testing audio circuits, the shortprod is removed and a shielded wire towhich two phone tips are soldered at

fOki/NE,INQLE AXON

BEND DOWCoNT AniNTED

ON roPOE Cl/Affi.14.

,Vg5

M

47z"Chassis layout of the compact signal tracer

one end and a pair of alligator clips atthe other end should be used. Theshielded wire should be plugged in atB and the shield should be plugged inat C.

There are many uses for this tracerthat you will find as you become betteracquainted with it, the time requiredto build it will be repaid many times.

PAPER TUBULARCAPACITORS

Good -All condensers are ideal for bothgeneral and critical application. The rangeof values will take care of any need inpaper tubular capacitors. Good -All con-densers are used by the millions by thegovernment in the V T Fuse and many ofthe largest Radio Mfrs. in the U. S.We specialize in making capacitorsto your specifications.FEATURES:

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New Direct -Coupled FM -A

AMPLIFIERMANUAL

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LAWS OF THE ATOM(Continued from page 31)

51. It was for this reason that Einsteinsuggested that studies of radioactivitymight show the EQUIVALENCE of massand energy.

52. Einstein's statement is that theamount of energy, E, equivalent to a mass,m, is given by the equation E.--:_mc2 wherec is the VELOCITY OF LIGHT.

53. From this equation, one kilogram (2.2pounds) of matter, if converted ENTIRELYinto energy, would give 25 billion kilowatthours of energy. This is equal to the energythat would be generated by the totalelectric power industry in the United States(as of 1939) running for approximately twomonths.

54. Compare this fantastic figure with the8.5 kilowatt hours of heat energy which maybe produced by BURNING an equal amountof coal.

55. Until the atomic power research pro-gram, no instance was known of matter be-ing converted into energy without moreenergy being used to produce the trans-formation than was released by it.

56. Two axioms of physics stated: (1)MATTER can be neither created nor de-stroyed ; (2) ENERGY can be neither cre-ated nor destroyed. For all practical pur-poses they were true and separate principlesuntil about 1940.

57. It is now known that they are, infact, two phases of a single principle, forwe have discovered that energy may some-times be CONVERTED into matter andmatter into energy.

58. Such conversion is observed in the

phenomenon of nuclear FISSION of uran-ium, a process in which atomic nuclei splitinto fragments with the release of an enor-mous amount of energy.

59. The extreme size of the CONVER-SION FACTOR explains why the equiva-lence of mass and energy is never observedin ordinary chemical combustion.

60. We now believe that the heat givenoff in such COMBUSTION has mass asso-ciated with it, but this mass is so smallthat it cannot be detected by the mostsensitive balances available.

61. Transformation of matter into energyis an entirely different sort of phenomenonthan the usual chemical transformations,where the matter is changed ino a differentform but its MASS persists.

62. From the standpoint of the Laws ofthe Conservation of Matter and of Energyalone, transformation of matter into ener-gy results in the DESTRUCTION of matterand CREATION of energy.

63. The OPPOSITE transformation, whichastronomers believe may be going on insome of the stars, amounts to the destruc-tion of energy and the simultaneous ,crea-tion of matter.

64. It is difficult for us to imagine thereconciliation of two such different conceptsas matter, with its characteristic mass orweight, and energy, which does not havethis quality. We shall, perhaps, be forcedto think of the stuff of the universe assome such combination of matter and en-ergy as would be symbolized by the coinedword "MATTERGY."

-Science Service, Washington

COMMON RADIO ABBREVIATIONSNo standard set of radio abbrevia-

tions is in universal use. The readerwill note slight differences in everybook or magazine he picks up. Thetable here is the result of a careful sur-vey of the best usage, and the readershould be able to interpret all regularradio abbreviations with its help. It isalso a safe guide for the radio writer.

Commonest variations from the listare the hyphenated adjectives, thus:r -f choke, a -c line. Many use capitalletters for the bulk of the noted ab-breviations, and in many cases periodsfollow one -word terms as well as thenarts of two -word abbreviations, whichare followed by periods in this table.

Certain terms describing Governmentagencies, complete pieces of apparatus,methods or systems have already beenaccented in practice as abbreviations in^anitals without no spacing or periods1,etween them. Examples are: FCC,FM, PA, PM. Another commonly ac-cented abbreviation is O.K., in capitalswith periods.

The only terms likely to cause con-fusion are those used to denote micro -henries and microfarads. The termmicro is here represented by the Greek

In some works, microhenry is de-noted by mh. Usually in such cases,millihenry is abbreviated Mh. Micro-microfarad may be represented in anyone of twelve ways: pµf, gufd, menf,mmfd, pf and pfd (picofarad) and byall the above followed lay periods.a.c. - alternating current

a.f. - audio frequencyAM - amplitude modulationamp - amperea.v.c. - automatic volume controlb.f.o. - beat frequency oscillatorcm - centimeterc.p.s. - cycles per secondc.w. - continuous wavedb - decibeld.c. - direct currentdx - distanceFM - frequency modulationh - henryh.f. - high frequencyi.f. - intermediate frequencyin. - inchkc - kilocyclekw - kilowattma - milliampereme - megacyclemeg - megohmmh - millihenrymm - millimeterPA - public addressPM - permanent magnet speakerr.f. - radio frequencyr.p.m. - revolutions per minutesec - secondt.r.f. - tuned radio frequencyu.h.f. - ultra high frequencyv - voltv.h.f. - very high frequencyw - wattsktf - microfaradwif - micromicrofaraduh - microhenry

In text it is preferable in most casesto spell out the less common or shorterterms in full.


POCKET RADIO CHECKER(Continued from page 22)

4 x 7 inches and are 3/16 thick. Sidesare 3 x 7 x 3/16 inches. For the endsh -inch thick material is used and thetwo pieces measure 3 x inches. Meterholes may be cut with a coping sawor circle cutter and then filed smooth.Three holes will have to be made inone end for power input, receptacle andpush button.

Making the ShuntsThese may be constructed with a fair

degree of accuracy and later adjustedto exact values. All the current shunts

Fig. 2-Facsimile of the special meter scale.

can be wound on one piece of plasticrod, the ohmmeter and condenser re-sistors on another. Exact value shuntsand resistors can be purchased, thussaving a lot of calibration.

Winding the copper shunts is just asimportant as is obtaining the correctlength of wire. Since copper stretchesvery easily no attempts should be made,to wind tightly. Loosely wound bobbinswill therefore be more accurate than anice looking tight -wound one.

5 feet 3-4/5 inches of No. 20 wire willequal .055 ohm. 5 feet 2% inches ofNo. 30 wire will equal .55 ohm. 57 feet6 inches of No. 30 wire will equal 6.05ohm. 42 feet 5% inches of No. 40 wirewill equal 45.4 ohms.

Odd value resistors may be made upby series or parallel combinations. 700ohms in parallel with 800 ohms willmake a 370 -ohm resistor. The 7800 -ohm resistor can be made up with a7500 -ohm and a 300 -ohm resistor inseries. MUltipliers are one watt unlessmarked otherwise.

Three types of markings are neededon the dial; an ohmmeter scale show-ing 45, 450 or 4500 ohms at the centerpoint; calibrations for 1, 10, or 100 d.c.ranges and an a.c. marking for makinglow voltage readings. These dials areavailable at most supply houses andcome in different types for the variousmeter makes. The correct dial for yourmeter is ordered by the meter model

number. The original 1-10 dial scalemay be used and charts made for a.c.,ohms and capacity scales. The scale inFig. 2 was drawn by the author, andrepresents several hours' work.

Calibration CheckWith the box made, shunts wound

and assembly completed, a check foraccuracy can be made. Exactness canbe compared with a quality multi -tester, and any inaccuracies adjusted.A substitution method for checking ispossible, if a good standard meter is

not obtainable for the calibration,thourh in most cases it will be pos-sible to borrow a voltmeter, ohm-meter or milliammeter, and checkone or more of the scales. If noneof these are obtainable, a fairlyaccurate check of voltages may bemade with new batteries of goodmake, with a bleeder across themto draw a small current. In somecases a voltmeter covering one ofthe scales may be obtained and abattery voltage measured exactlywith it, then used to calibrate otherscales.

Precision resistors plus knownvoltages may be used for checkingmilliammeter scales (a 500 -ohm, 5 -watt, and a 50,000 -ohm unit willbe found very useful). In suchcases, low -resistance sources should

be used. For example, a 50 -volt B bat-tery will probably not maintain itsvoltage if subjected to a 100 -ma drain,where a storage battery will delivermany amperes without drop.

For drains of a few milliamperes,heavy-duty B batteries will be foundsufficiently stable.

Resistance scales are checked withprecision resistors of known value.Readings of the ohmmeter should com-pare favorably with the known resistorvalues. The resistors can be used in thefuture to check the ohmmeter batteries.

Failure of the meter to show the cor-rect value will indicate that the batteryhas run down too far to be useful.

The capacity scales may also bechecked with the two resistors. A read-ing of .66 milliampere should be ob-tained on the C x 1 range for 50,000ohms, .13 for 50,000 ohms on C x 10and .54 for 500 ohms on the C x 100range. If these three readings are ob-tained, the scale which accompaniesthis article will be correct for yourmeter (based on 1 milliampere d.c.scale). Since a.c. is measured on thesame shunts as d.c., separate calibra-tion is unnecessary. This completes thecalibration of the wide range pockettester. Constant usage will soon makeit the handiest piece of test equipmentin your shop and its small size makesit a handy instrument for outside jobs,where it can be used to perform awider variety of jobs than most metersof comparable bulk and weight.

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Elementary Engineering ElectronicsWith Special Reference to Measurement and

Controlby Andrew W. Kramer

Managing Editor, Power Plant EngineeringMember American Institute of Electrical

EngineersAssociate Member Institute of Radio EngineersThis is a PRACTICAL treatment of principlesand applications-non-mathematical.

ORDER THIS UNIQUE BOOK NOWCheck, money order or cash must accompany

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InstrumentsTHE MAGAZINE OF

Measurement and ControlOffers a balanced diet of articles and specialfeatures appealing to production men as wellas to research men - to executives andapprentices.

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Instruments Publishing Co.1132 Wolfendaie St., Pittsburgh 12, Pa.

1--1 Enclosed is $2.00 for which send meI-I Kramer's ELEMENTARY ENGINEERING

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1947 RADIO -ELECTRONICS REFERENCE ANNUAL, 47

MAXIMUM FIDELITY(Continued from page 3)

reduced greatly over the conventionalopen -back enclosure.

When a speaker is placed in an en-closure of this type, the back wave ofthe speaker is added in phase with thefront wave through the port in thecabinet, which adds to the acoustic pow-er obtainable at low frequencies. As amatter of fact, the radiation from theport exceeds the radiation from the coneat very low frequencies. This increasesthe low -frequency response, extendingit approximately an octave lower, whileat the same time more heavily dampingthe frequencies above this point. Thistends to smooth out the response fromthe lower limit up.

Damping material is placed in thebaffle behind the speaker to absorb theback wave. If this were not done, itwould reflect from the back and cancelsome of the higher frequencies emerg-ing from the cone. This would give riseto very uneven high -frequency response.The overall effect is an enormous im-

o

%SOL ,40606.3V

should match your individual speaker.The dimensions given are approximateand there are two ways to vary thebox's resonant frequency.

The easiest method is to vary theport size by placing a book over partof it while feeding several volts of 60 -cycle a.c. into the speaker voice coilfrom a filament transformer. When theproper size is arrived at, a piece ofwood may be screwed over part of theport inside the box. The right positionis where the greatest amplitude appearsat 60 cycles.

The more difficult method is to movethe back of the baffle in or out of thebox until the desired result is obtained.For the 15 and 18 -inch speakers itwould be desirable to use a 30 or 40-cycle source for adjusting the baffle.The source should be a high -qualityaudio oscillator, with low distortion.

For AM or shellac pressing reproduc-tion, a single speaker with response upto 5000 or 7500 cycles will be adequate.

For FM or fran-c- scription reproduc-

tion, better resultscan be obtainedwith a dual speak-er system, with asmall high -frequen-cy speaker addedto extend the rangeof the larger unit.

Several coaxial units are available,ranging in price from $30 to over $250.

Photo C shows a Jensen 18 -inch lowfrequency speaker, a 14 -inch speakerand a Jensen C3 tweeter. This com-bination is capable of reproducing therange from 30 to over 15,000 cycles.

BIASVOLTAGE

117V AC '6001Fig. 5-Simple bias supply which works from the power transformer.

provement in the bass and a clear highfrequency response.

The baffle in Photos A and B wasbuilt for an 18 -inch speaker, but thistype of baffle works wonders on anysize speaker. Fig. 6 gives the dimensionsfor all standard sizes. The enclosure

Photo C-A combination of speakers to provide high fidelity from 30 to 15,000 cycles

The best place for a speaker in anyroom is in a corner facing the longestdiagonal. In this position the enclosureis best able to match the room's acousticimpedance. Place the speaker farenough from the turntable so acousticfeedback will not occur from mechan-ical coupling at low frequencies.

DIMENSIONS BELOW IN INCHES

S ABCDE PORT8 24 18 II 7 3 1/2 AREA OF SPEAKER HOLE " "D10 28 ..

" "12 31 24 13 II 3.5

,. ,, .

15 34 26 14 13.5 4 9/16 " " -18 40 27 14 16 4.5 5/8 - - " - '

Fig. 6-Correct dimensions of speaker baffle(The first column "5" shows speaker diameter)

HAIRFELT ORGLASSWOOL

BACK VIEW BACK

Don't ruin records with worn needles.A regular steel needle will play oneside of a 12 -inch disc and should not beused further, as it will develop a pro-nounced fiat spot with a sharp cuttingedge which will tear up the next record.It will also allow the pickup to chatterin the groove, giving rise to a particu-larly obnoxious type of distortion.

It is a good investment to purchasea pickup with a built-in permanentstylus. The pressure on the record ofthese units is usually less than thereplaceable -needle types. There is muchless acoustical chatter, the hiss is lowerand the sapphire stylus is kinder toyour records.

In the case of transcriptions, it isnecessary to use a light -weight pickup,preferably with sapphire or diamondneedles. The one greatest cause of sur-face noise on records is dust. Theyshould be stored in dustless envelopes.


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Developed for all amplifier applicationsrequiring a wale pass -band and lowinherent amplitude and cross -modula-tion distortion. Particularly adapted forstudio monitoring, record evaluation,microphone and speaker measurements,as well as absolute -fidelity amplificationof FM and AM radio programs and alltypes of recording.

SPECIFICATIONSTUBES REQUIRED: 2-12SC7, 2-12SK7, 2-6SC7, 2-6W, 2-6L6G, 1-5V4G, 1-5U4G, 1-BBROVERALL GAIN: Phono-Radio; 96 DBNO. OF STAGES: FiveRATED POWER OUTPUT: 23 WattsHARMONICS AT RA11.°D OUTPUT: Less than 1%HAMONICS AT 1/2 RAIED POWER: 0.5%NOMINAL POWER OUTPUT: 35 WattsHARMONICS AT NOMINAL POWER OUTPUT: Less than 5%PEAK POWER OUTPUT. 39 WattsHUM AND NOISE LEVEL: -40 VUMUSICAL RANGE ± 1 DB: 10 OctavesNORMAL RESPONSE ± 1 DB: 20 to 20,000 CyclesCONTROLS: Radio, Phono, High Frequency, LoW Frequency, Expander -

Suppressor, Timing, Master Gain ControlHIGH FREQUENCY CONTROL RANGE: From +13 db to -8 db at 10,000 CyclesLOW FREQUENCY CONTROL RANGE: From +14 db to -8 db at 100 CyclesDIALOGUE FILTER RANGE: -10 db at 50 CyclesEXPANSION RATIO: Adjustable up to 10 dbEXPANDER TIMING CONTROL: Adjustable from 0.05 to 0.5 secondsSCRATCH SUPPRESSOR: Non -Frequency DiscriminatingSCRATCH REDUCTION: 10 dbDYNAMIC RANGE: 83 dbINPUT CHANNELS: TwoINPUT IMPEDANCES: 500,000 OhmsMINIMUM INPUT SIGNAL: Phono or Radio Input; 0.02 VoltsOUTPUT TERMINALS: 4/8/16/500 OhmsBETWEEN TERMINALS: 1/2/6/10/12/83/100/125/150/166 OhmsLINE VOLTAGE: 105/120 Volts 50/60 CyclesPOWER CONSUMPTION: 150 WattsSWITCHES: Expander, Dialogue Filter, Scratch Suppressor, On -OffDIMENSIONS: 17" x 10" x 10"NET WEIGHT: 40 Lbs.SHIPPING WEIGHT: 55 Lbs.MODEL NO.: ACA -100 DCGUARANTEE: Five YearsLIST PRICE: $312.00NET PRICE: $187.20MATCHED SET OF TUBES. NET PRICE $12.07 'Trademark Registered U. S. Patent Office.

AMPLIFIER CORP. of AMERICA396 Broadway New York 13, N. Y.

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ake a genuine "Sealdtite" capacitor and try to squeeze it. No "soft spots."Why? Because this Solar capacitor has its high purity paper -and-foil -winding ingeniously molded into a cylinder of solid wax.

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