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10 -CRAFT LIBRAR

MODERNVACUUM

TUBESAND

How They Workwith complete technical dataon all standard tubesand many special tubes

y Robert Hertzberg

PUBLISHED ByNSBACK PUBLICATION'S I9ik PARK PL ACE N EW YORK n

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Auto -Radio .

Service Manual!;:,*

Complete Directoryof on

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' Full Installation andTrouble Shooting Guide

Over 200 Pages

Over 500 Illustrations

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Every man connected in any way withthe booming auto -radio business will wanta copy of this book immediately. It is de-voted exclusively to auto -radio service"dope" in complete, understandable form.The OFFICIAL AUTO -RADIO SERVICEMANUAL contains schematic diagrams,chassis layouts, mounting instructions, andtrouble shooting hirts on all 1933 and manyolder model auto -radio receivers. ThisManual contains a "gold -mine" of inform-ation.

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ISend remittance of $2.50 in form of Check or Money Orderfor your copy of the 1933 OFFICIAL AUTO -RADIOSERVICE MANUAL. Register letter if it contains cashor currency. THE MANUAL IS SENT TO YOU POST-AGE PREPAID.

GERNSBACK PUBLICATIONS, Inc.96-98 VT PARK PLACE NEW YORK, N. Y.

MODERNVACUUM

TUBESa I I (I

How They Work

With Complete Technical Data on AllStandard Tubes and Many Special Tubes

by Robert HertzbergCornpretely revised by J. T. Bernsley

GERNSBACK PUBLICATIONS, Inc.Publishers

98 PARK PLACE NEW YORK, N. Y.

Table of Contents

Chapter 1-The Edison Effect and the Electron Theory 4-7

Chapter 2-Electron Emitters and the Ionization Effect 8-9

Chapter 3-The Three -Electrode Tube 10-16

Chapter 4-Vacuum Tube Characteristics, Definitions 17-18

Chapter 5-Four- and Five -Element Tubes 19-22

Chapter 6-Light Sensitive Cells and Other Special Tubes 23-26

Special Overhead Heater Tubes 27

"Exploded" Views of Tubes 28-29

Average Characteristics of Radio Tubes 30-41

Tube Symbols 42-43

Tube Connections and Tube Symbols 42-43

Tube Applications and Circuits 44-48

Application Notes on 37, 56, 57 and 77 Tubes 49

New and Special Tubes 51-54

Advances in Tube Design 55-57

Second Reprint

Completely Revised

Printed in U. S. A.

Copyright 1934 by (1. P. Inc.

PrefaceTHE vacuum tube is unquestionably the most im-

portant single device used in radio, and is becom-ing increasingly important in many other phases ofthe electrical art. Its fundamental theory should bethoroughly understood by every radio Service Man,experimenter and constructor; the man who is ignor-ant of this theory works eternally in the dark.

The operation of vacuum tubes is not particularlysimple, since it involves such intangible things aselectrons, but this little book will help clarify it inthe minds of willing students. The use of mathe-matics has been avoided, and explanations are giveninstead in more easily understood physical terms. Aknowledge of ordinary electricity on the part of thereader is presumed, so the text is devoted entirely totube phenomena. All types of present day tubes fromdiodes to pentodes are described and their character-istics given in detail. The various charts and curveswill be found particularly valuable for referencepurposes.

The reader is cautioned not to try to read andabsorb all the information in this book at one sitting.He should study chapter by chapter, reading eachone two or three times, until all the facts becomefixed in his mind. Hasty reading is worse than noneat all, as a thin skin of unrelated data makes forconfusion rather than clarity.

-The Author.

Revised by J. T. Bernsley

CHAPTER 1

The Edison Effect and the Electron Theory

Edison Effect:

DURING the course of his develop-ment work on the electric light.

Thomas A. Edison performed thousandsof experiments with different conduct-ing materials sealed inside evacuatedglass vessels. In 1884 he constructed apeculiar bulb having an ordinary car-bon filament and also a small metalplate completely insulated from the fila-ment. When this lamp was connectedin the simple circuit shown in Fig. 1,

FLATE

GALVANOMETER

FILAMENT

.01

BATTERY BATTERY

FIG. IT -

This simple circuit Illustrates the EdisonEffect. When the filament is lightedand the plate made positive, the gal-vanonwtor will indicate a flow of currentIn the series eirenit.

and the filament was lighted to incan-descence, the sensitive galvanometershowed a reading. This indicated thata current of electricity was flowingthrough the circuit in spite of the factthat the filament and the plate of thetube were separated by a vacuum,which was known to be nonconductive.The galvanometer needle showed a de-flection only when the positive pole ofthe "B" battery was connected to theplate. If the polarity was reversed nocurrent flowed. The current flow couldalso be stopped by turning off the fila-ment.

To Edison, who was seeking a per-fect filament for his electric light, thiseffect was interesting but without par-ticular significance. He recorded hisobservations and proceeded with otherexperiments. Later, the action becameknown as the "Edison Effect" and wasfurther investigated by other scientists.

Out of it grew the modern vacuum tube,which is the very heart of present dayradio.

Electron Theory:

How did the current get through theapparently impassable barrier insidethe tube? In 1884 Edison himself couldnot answer this question, but to -daywe can explain the phenomenon quitesatisfactorily with the aid of the elec-tron theory. According to this theory,which is generally accepted, all sub-stances consist of myriads of atoms,each atom being made up of a centralnucleus surrounded by a number of"electrons". The nucleus is conceivedas having a positive charge of elec-tricity, and the electrons as having neg-ative charges. Under normal condi-tions the positive charge is equal instrength to all the negative charges ofthe electrons put together. so thecharges balance each other perfectlyand there is no outward electricaleffect. However, inside the atom itselfone or more electrons is free to movearound. In poor conductors of elec-tricity the electrons are pretty well im-prisoned. In good conductors a lot ofthem are likely to be running loose.Inert, "dead" materials like wood, ce-ment, rubber and cotton are poor con-ductors, so poor, in fact, that they areknown as "insulators"; electronicallyspeaking, as they are very inactive. Allmetals, to a varying degree, are goodconductors, because the electrons oftheir atoms are lively and active.

Now at ordinary temperatures theelectrons do not have sufficient velocityto break through the surface of eventhe most conductive metals. However,when a metal is heated, the atomicagitation increases rapidly and finallya point is reached where some of theelectrons are forcibly flung away fromthe surface of the material and form a

4

MODERN VACUUM TUBES 5

cloud over or around it. The metal ac-tually evaporates, just as water does.This action is known as "electronicemission," and can be defined as thesetting free of electrons.

As the electrons have a negativecharge, their departure from the nuc-leus disturbs the previous state of bal-ance, and the positive charge of thenucleus more than equals the negativecharges of the remaining electrons. Thenucleus thus tends to attract or pullback the free electrons and does not letthem go very far.

For the actual emission of electronsthe metal must be heated to incandes-cence in a vacuum, as otherwise it com-bines with the oxygen of the air andsimply burns up. The most convenientway to obtain emission of this kind isto heat a filament or wire inside anevacuated glass bulb by a current ofelectricity. Some substances throw offelectrons more freely than others, andat lower temperatures.

The Edison Effect now almost ex-

plains itself. The filament of Edison'slamp, burning at red heat, emittedelectrons. The metal plate, beingcharged positively, attracted some ofthese electrons and caused them tobreak away from the cloud surround-ing the .filament. As free electrons inmotion constitute an electric current,the galvanometer indicated a currentflow. (The direction of the currentflow is conventionally considered as op-posite to that of the electron stream.)The current registered by the meter isknown as the "plate current."

Secondary Emission:

The plate or second element in thelamp must be relatively cold. If itwarms up appreciably, because of ra-diation from the filament or because ofthe bombardment of the electrons strik-ing it, it will emit electrons of its ownand these of course will repel the fila-ment electrons, thus neutralizing theeffect of the positive plate potential.This effect is known as "secondary emis-sion" (as distinguished from the prim-ary emission of the filament) and shouldbe remembered because it plays an im-portant part in the operation of am-plifier tubes.

Factors Determining Plate Current:

In a two -element tube of given con-struction, the actual amount of platecurrent depends on two factors: the fila-ment temperature and the plate volt-age. If the filament is maintained ata certain heat, it will emit a certainquantity of electrons per second. Theproportion of these reaching the plateis determined by the plate voltage. Asthis voltage is gradually raised fromzero, more and more electrons will reachthe plate and the plate current will riseaccordingly, until a point is reachedwhere all of the available electrons areattracted to the plate. Raising the volt-age beyond this point does not increasethe maximum plate current, which isthen known as the saturation currentfor the particular filament temperatureor plate voltage. A further increasein plate current can be obtained only ifthe filament is made hotter, and thenanother saturation point will be reached.This effect is illustrated in Fig. 2.

2

FIG.2

FILAMENTCURRENT

FILAMENTCURRENT

1

10 20 ]0 60 50 6010 80 90 100 110 120130140

PLATE VOLTAGE

This curve illustrates the increase Inplate current obtained by raising thetemperature of the filament. Saturationis reached at the point where the curveflattens out at the top. The valuesIndicated are purely relative and do notapply to any particular tube.

Space Charge:

If the plate potential is kept at afixed value, and the filament tempera-ture raised gradually from a cold start,a similar limiting action takes place,but through a different cause, known asthe "space charge" effect.

The space between the hot filamentand the cold plate contains the elec-trons emitted by the filament. They areabsorbed by the plate as long as theplate's rate of attraction is greater thanthe filament's rate of emission, and theplate current climbs accordingly. Ifthe filament temperature is raised highenough, the electrons will become so

6 MODERN VACUUM TUBES

dense that their overall negative charge,culled the "space charge," is equal tothe positive charge of the plate, and theplate current will not increase with fur-ther increase of filament heat. In otherwords, saturation has been reached forthat particular plate voltage. Comparethis effect with the one described in thepreceding paragraph. When the fila-ment temperature is raised beyond thissaturation point, the space charge over-comes the plate charge, and any addi-tional electrons from the filament arethrown back, in accordance with thefundamental law of electricity that likecharges repel each other. In order toovercome the space charge and to ob-tain greater plate current, the platevoltage must be increased. See Fig. 3.Of course, both filament temperatureand plate voltage cannot be increasedindefinitely. The filament will burn outeventually, or the glass insulation ofthe bulb will break down under thestrain of the high voltage.

5

Z w 4ttWw,yIra 3

4- 2-J1- -/

PL ATEVOLTA GE

PLATEVOLTAGE

1

.05 .1 .15 .2 .25 .3FiG.3 FILAMENT CURRENT

The plate current stops increasing withincreasing filatnent current nt a pointdetermined by the spnee-charge effect.The latter can be overcome only by rais-ing the plate voltage. In this curve a ISOthe flat upper section represents thecondition of saturation.

Fleming Valve:

The first practical use of the two -element tube or diode was made in 1890by Dr. J. A. Fleming, a famous Eng-lish scientist. The Edison lamp as heemployed it for radio work is stillknown as the Fleming valve.

Since current will flow through thediode only when the plate is positive.the tube is a simple and perfect recti-fier of alternating current, and foundemployment as a detector in the earlydays of wireless. Rectification is sim-ply the changing of alternating currentinto direct current. When connected inan elementary receiving circuit such asshown in Fig. 4, the diode rectified

radio frequency damped wave or"spark" signals, leaving an audio fre-quency component to which the ear -

LOOSE TUNING RHEOSTATCOUPLER CONDENSER

DIODE

PHONES

FIG. 4 "A- BATTERY

The Iwo -element tube. when used in thecircuit above, makes an effective detectoror teetitler of radio-frequeiwy currents.'Phis elementary circuit was used at onetime for I he reception "spark- sig-nals from old-fashioned transmitters.

phones would respond. No plate or "B"battery is needed, as the incoming sig-nal provides the plate energizing po-tential. During that part of the cyclewhen the plate is positive in relationto the filament, electrons are attractedto the plate and a pulse of current flowsthrough the earphones; when the cur-rent reverses and the plate becomesnegative in regard to the filament, theelectrons are repulsed and that half ofthe cycle is eliminated. The net re-sult is a series of audible current pul-ses, all flowing in one direction throughthe phones.

The diode detector was not particular-ly sensitive, and soon gave way to thethree -element tube, or triode, developedby Dr. Lee de Forest in 1907. This isdescribed in chapter 3.

Diode Rectifier:The diode as a rectifier of alternating

current has survived as an exceedinglymeritl and valuable device. The 281and 280 rectifier tubes now in commonuse are ordinary two -element bulbs.differing very little in construction fromEdison's original experimental lamp of1884. The 281 is a true diode, contain-ing a single filament and a single plate,and is used for "half -wave" rectifica-tien. The 280 is really two diodes inone glass envelope, having two filamentsand two plates, and is used for "full -wave" rectification. Two 281's may beused for full -wave rectification just aseasily as a single 280.

Because of the widespread misunder-standing of rectifier systems, an ex-


planation of the half -wave and full -wave methods is in order. A simplehalf -wave circuit is shown in Fig. 5.The primary of the power transformeris energized by the usual 110 volt, 60cycle line. One end of the secondaryu hiding is connected to the plate of the281 rectifier tube, and the other endforms the negative side of the output,running to the load resistance. Theether secondary winding merely lightsthe filament of the tube.

POWER 281TRANSFORMER RECTIFIER

IPRIMARY FILAMENT WINDING

FIG. SA

FIG.5

Illustrating the circuit and action of ahalf -wave redifier of alternating current.Note from I ic. ni; that the outputcurrent i. 11..1 continuous, hut has ;zapsin it.

The alternating current as it entersand leaves the transformer has the us-ual sine wave form shown in Fig. 5A.On the first half of the cycle, when theupper end of the secondary is positiveand the lower end negative, the plate ofthe tube is charged positively, electronsare attracted and the current passesthrough unchanged in form, as indicatedby the first pulse of current in Fig. 5B.When the current changes in direction,the upper end of the secondary becomesnegative, the electrons are repelled, andno current flows. The entire circuit isthus really open for the length of timerepresented by the first shaded area ofFig. 5A. When the next cycle beginsand the upper end of the secondary oncemore becomes positive, current againflows, as represented by the secondpulse of current in Fig. 5B. This opera-tion keeps repeating itself, so the outputof the system is a series of direct cur-rent pulses, the time interval betweenthem being equal to their own duration.This pulsating direct current, for re-

et:lying purposes, must be smoothed outby large filter systems.

It is obvious that the half -wave rec-tifier is only 50% effective, since onlyhalf of the alternating current wave isused. In the full -wave system, asshown in Fig. 6, both halves of thewave are utilized, and the current out-put is twice as steady. Here the powertransformer secondary is tapped in thecenter. During one-half of the a.c. cycle,the top of the secondary is positiveiii relation to the center, and the bottom

In the full -wave rectifier, loath halves ofthe alternatinv: current wave are used,pml the eat eat current. ns showneranhically in 1.1g. OK is much smootherthan the output of a half -wave rectifier.

is negative. This means that the topplate of the 280 rectifier is positive, andthe bottom plate is negative, and there-fore all the electrons are attracted tothe top plate and current flows throughthe circuit. When the a.c. reverses itsdirection, the top plate becomes nega-tive and the bottom positive, and thencurrent flows again. Note that in eitherease, the current flows from one plate,through the filament, out through theload resistance, and back through thecenter tap connection. Both halves ofthe a.c. wave flow in the same directionin the output circuit, as shown in Fig.6B.

Two 281's are usually used in a full -wave circuit to obtain direct current athigh voltage for the operation of poweramplifiers and transmitters. Two sep-arate tubes withstand the voltage strainbetter than a double tube like the 280,which is satisfactory for lighter dutyin receiving sets. Both tubes developconsiderable heat during normal opera-tion.

CHAPTER 2

Electron Emitters and the Ionization Effect

Since the life as well as the funda-mental action of a vacuum tube dependson the filament, this element is a veryimportant one and has received thebenefit of considerable research.

Tungsten Filaments:

Early radio tubes used pure tungstenwire for their filaments. This wasburned at a bright white heat to giveadequate electron emission, and wasnot altogether satisfactory because itwas erratic in behavior and short inlife. Later, engineers found that asmall amount of the metal thorium,added to the tungsten in the process ofmanufacture, acted as a coating for thelatter and vaporized from the surface inthe form of a strong electron flow. Infact, for the same normal filament tem-perature a thoriated tungsten filamentgives twenty times the electron emis-sion of a pure tungsten filament. Prac-tically all of the millions of battery typetubes of the 201A variety used thoriatedtungsten filaments, which operate at atemperature of 1800 degrees.

A. C. Tubes:

So far we have assumed that the fila-ment is being heated by batteries,which give smooth direct current. Asthe demand grew for "electric" radioreceivers that would operate off the a.c.line, tube designers found it necessaryto seek new filament constructions, asthoriated tungsten is not suitable fora.c. use. The thin wire, carrying onlya fraction of an ampere, responds read-ily to the 120 current pulses that takeplace every second in a.c. circuits, andthe electron stream fluctuates at thesame rate. This fluctuation makes it-self heard in the loud speaker as a dis-agreeable hum. The first a.c. tubes, ofthe well known 226 type, used heavyoxide coated filaments operating at acomparatively low temperature with

stepped down raw a.c. at a little morethan an ampere of heating current. Theheavy wire and the low temperaturegive the wire considerable thermal in-ertia, so it does not respond readily tothe quick variations of the alternatingcurrent.

The coating on the filament is an ox-ide of either barium or strontium, andthe filament itself is platinum, nickelcr a special alloy. The electrons areemitted by this coating, and not by thefilament itself, which serves only as a

titer. Although the oxide coated fila-e I lit burns normally at only 1300 de-g as compared to 1800 degrees forti ,,tinted tungsten, it gives six timesthi electron emission. Practically allpresent-day tubes taking raw a.c. ontheir filaments are of the oxide -coatedtype.

Ile:fled Cathodes:

THIMBLECOATED

WITHELECTRONEMITTING

MATERIAL

This exaggerated view shows the con-strue' ion of the heated cathode used inthe nudority of present-day A.C. tubes.The filament in this case is merely aheater.

Although the oxide -coated filamentreduced hum a great deal, it was stilltoo noisy for satisfactory use in detec-tor tubes. To overcome this shortcom-fig, engineers developed the cathode orindirect heater type of tube. Here theelectron emitter is a tiny, hollow thim-ble of insulating material, coated on theoutside with one of the efficient elec-tron -emitting oxides. See Fig. 7. A

8


wire, energized by raw a.c., runsthrough the center of this thimble, andheats the element sufficiently to causeit to emit electrons. A separate con-nection is made for the thimble, whichis called the cathode. The filament inthis type of tube is merely an accessory,and has no connection with the receivercircuit proper.

Cathode heater tubes are not limitedto use on alternating current only.They can be heated just as well by bat-tery current. In fact, the "automobile"series of battery tubes uses the cathodeheater construction because it is ruggedmechanically and flexible electrically.The fact that the electron emitting ele-ment requires only one connection, in-stead of two as in the case of regularfilament types, makes the tube veryconvenient for many special purposes.Heated cathodes are now quite univer-sally used, even in some diode rectifiers.

At the present time there is no sim-ple and practical means of obtainingelectronic emission for radio purposeswithout the use of heat. However, anumber of experimenters are workingon a "cold" tube, and developmentsalong this line appear to be promising.

Ionization:

In the foregoing discussion of tubetheory it has been assumed that theglass bulb containing the filament andplate electrodes is perfectly evacuated.If it is, the electron effect takes placeprecisely as described. However, ifthere is even a slight trace of air orother gas left in the tube, the action iscomplicated by a phenomenon known as"ionization." This is simply the processof losing electrons from an atom, and

the part left behind after the electronsdepart is called an "ion".

The atoms of any gas are normallyin an agitated state, and can readily bebroken up. This is just what happensto the gas atoms left in a vacuum tube,particularly when the plate voltage ishigh. The electrons emitted by theregular filament or cathode assume arather high velocity under the urginget the positively charged plate, and intheir hurry to get to the plate they col-lide with the gas atoms and knocksome of their electrons loose. Theseelectrons, being negative charges, arealso attracted by the plate and serve toincrease the plate current. This effectis known as "ionization by collision."

While it may appear to be helpful be-cause it increases the plate current, itIs undesirable because it makes the op-eration of the tube erratic. If the glassbulb is poorly evacuated the electronflow may be so heavy as to be uncon-trollable. Also, it appreciably shortensthe life of the tube, because the ions,being left charged positively by the es-cape of the negative electrons, are at-tracted violently to the highly negativefilament and actually tear away its sur-face because of their great mass. Ion-ization in a tube is invariably accom-panied by a characteristic bluish glow,although in some tubes a glow may bedue to other causes which are not harm-ful.

Highly evacuated tubes are said to be"hard". Gassy ones are called "soft".With the perfection of pumping equip-ment, practically all modern vacuumtubes are of the "hard" type. When atube absorbs gas through microscopiccracks or other causes it is said to havebecome "soft" or "gassy", and is usuallydiscarded as undependable.

CHAPTER 3

The Three -Electrode Tube

"C;rid" Electrode:

In 1907 Dr. Lee de Forest added athird element, called the "grid", to thetwo -element tube, and produced one ofthe most useful and versatile devicesknown to modern science. This grid ismerely a helix of fine wire placed be-tween the filament and the plate andcompletely insulated from both. A sin-gle connection wire runs from one endout through the glass. See Fig. 8.

The three -element tube or "triode" hasa grid encircling the filament. This ele-ment thus can control the electron streamfrom the filament to the plate.

Since the grid is open in construction,it does not appreciably obstruct thenormal electron flow from filament toplate. However, if it is given an elec-trical charge it will naturally have someeffect on the sensitive electrons. If itis made positive in relation to the fila-ment, it helps to break up the spacecharge, accelerates the electron stream,and produces an increase in plate cur-rtnt. It also acts as a plate and ab-sorbs a few electrons itself, but sincethe surface of the thin wire is small,most of the electrons rush right throughto the plate, and the grid current (fromgrid to filament) is infinitesimal com-pared with the plate current. If thegrid is made negative it strengthensthe space charge and repels the emittedelectrons, causing a decrease in platecurrent.

Amplification Factor:

The important feature of this three -electrode arrangement is that the grid,

being much closer to the filament thanthe plate, can control the electronstream (and hence the plate current),much more effectively than the plate it-self can. A voltage applied to the gridwill produce a much greater change inplate current than exactly the samevoltage applied to the plate. For in-stance, let us take a theoretical tubeand put two volts on the grid. Theplate current increases say four mil-liamperes over its previous value, witha certain value of plate voltage. Toobtain an equal increase in plate cur-rent by means of the plate alone, theplate potential must be raised consider-ably more than two volts. If the tubewere a 201A, the increase would haveto amount to 16 volts. The ratio of thechange in plate potential required tovary the plate current a given amount,ti, the change in grid voltage to pro -

same variation, is called the"voltage amplification factor" of thetube. It is usually represented by theGreek letter "mu." In the case just&scribed the ratio is 16 to 2, or 8 to 1,and the mu of the tube is then said tobe 8.

Characteristic Curves:

The properties of the three -elementtube can best be understood from astudy of a set of typical characteristiccurves, as shown in Fig. 9. These are

90V. PLATE

45 V PLATE

22V. PLATE

10 8 6 4 2 0 2 4 6- GRID VOLTAGE. +8 10

2422208 t '1 it ;f),16 cc

14 cc w12 ?,10 -8 W46 et j4 -a cl

I z

FIG. 9

These typical curves show how the platecurrent of a three -element tube varieswith different grid and plate voltages.Notice how sharply the plate currentrises when the grid is made positive.

10


TUBE

4:11:1GRID

VOLTMETER

-1101 4H1111----ThATTERY

BATTERY111.0 toi,ATTERY

PLATEMILLIAMMETER

FILAMENTRHEOSTAT

FIG. 10 V,_ PLATE VOLTMETER

The curves of Fig. 9 may be obtainedquite easily with this circuit. Onlythree small meters are required, in ad-dition to the usual filament, grid andpiste butteries.

easily obtained by connecting the tubein a circuit such as shown in Fig. 10,and simply noting the meter readingsas the various voltages are varied.Three curves are shown, for three val-ues of plate voltage, 22, 45 and 90 volts.With the voltages fixed at these values,the grid bias is changed over differentpositive and negative values, and thecurves then indicate the correspondingplate current variations. Notice thatwhen the grid is positive the plate cur-rent rises sharply; when it is negativeit drops off. There are two distinctbends or "knees" in each curve, one atthe top and the other at the bottom.The curves flatten out at the top aftera certain positive grid potential or biasis reached, and no further increase ofplate current results from further in-crease of the bias. This condition mere-ly represents saturation. Increasingthe bias negatively enough eventuallyshuts off all the plate current.

Now in radio reception we are inter-ested in doing two things: amplifyingthe weak signal impulses picked up bythe antenna and then detecting them sothat they can be heard through ear-phones or a loud speaker. The three -element tube lends itself admirably toboth purposes.

Action as Amplifier:

For use as an amplifier, the tube issimply operated along the straight sec-tion of the grid voltage -plate currentcurve. The action is made plain inFig. 11. The value X represents theideal grid bias, as this point on the

curve is the center of the straight sec-tion. If we now impress the weak sig-nal current having the amplitude a -a onthe grid of the tube, the grid bias willbe swung back and forth according tothe fluctuations of the current. Theplate current will fluctuate in exactlythe same fashion, as the grid modulatesthe electron stream perfectly. How-ever, the amplitude of the plate currentvariations, b -b, will be much greaterthan the original signal amplitude.

It can be seen that the grid has a"trigger" action, and allows smallvoltages to control the comparativelylarge power in the plate circuit.

It is quite possible to connect a wholeseries of amplifier tubes in a suitablecircuit so that the plate current varia-tions of the first one operates the gridcircuit of the second, and so on downthe line. In this way even a very weaksignal can be brought up in strengthby the overall repetition effect. Am-plifiers are sometimes called "repeaters"because of this successive action. Asmany as fourteen "stages" of amplifi-cation have been used successfully toamplify extremely weak radio -frequencysignals.

The frequency of the current fed tothe grid of a three -element tube doesnot affect the amplifying action in theslightest, as the electron stream has noappreciable inertia and responds in-stantly to both the lowest and the high-est frequencies encountered in radio andgeneral communication work. The onlylimitation in this respect is imposed by

If a three -element tube is operated onthe straight section of its characteristictine, it will faithfully reproduce any

alternating current impressed on its grid.The amplitude of the plate currentvariations represents amplification of the


the incidental capacity effect of thetube elements themselves. This will bediscussed in the section on screen -gridtubes.

Action as Detector:

After a radio signal has been ampli-fied, it must be "detected" or loweredin frequency so that it will be audibleto the human ear through earphonesor a loud speaker. Bear in mind thatradio waves as they are transmittedare at very high frequencies, much be-yond the limit of audibility, which isonly about 20 kilocycles. The three -element tube makes an excellent de-tector if it is operated in either of twoconnections.

Grid Bias Detection:

The first method is the grid biasmethod, and is also known as the"power detection" or "plate rectifica-tion" system. It depends on the lowerbend found in the characteristic curvesof all three -element tubes. Refer toFig. 12, which illustrates the actiongraphically.

if a three -element tube is operated onthe bend or "knee" of its curve, it willtend to amplify one half of the signalwave more than the other. Notice thedifference in height between "b" and "c."

If the point X is selected on thecurve, and the grid bias adjusted tothis point, the plate current will notfaithfully reflect the grid voltage var-iations, but instead will tend to distortthem. Suppose we take a modulatedsignal and impress it on the grid. Ithas the amplitude a -a, and, of course,like all good alternating currents, the

respective alternations on both sides ofthe zero line are of equal height. Nowfollow the wave form as it hits the

A "-Va

SIGNAL POTENTIAL AND GRID POTENTIAL

PLATE CURRENT VARIATIONS

EFFECTIVE CURRENT THROUGHFIG.13 PHONES

These three curves illustrate the detect-ing action of a three -element tube oper-ated in the manner shown in Fig. 12.Tlie little bumps below the time axis arepraci teeny eliminated.

curve, and you will observe that thealternations in one direction are ampli-fied considerably in the plate circuit(b), while the other alternations pro-duce only little bumps The effectof every complete cycle of current isthen a large increase and a small de-crease of plate current. The decreasesof current are so small, compared tothe increases, that the alternating cur-rent is practically rectified, and thecurrent in the plate circuit of the de-tector tube is then virtually a seriesof unidirectional pulses. They are stilltaking place at high frequency, butbecause of the inertia of the dia-phragms of earphones and loud speak-

TUNINGiCIRCUIT

'CT BATTERY

(FOR GRID BIAS)

"A" BATTERY.FIG. 14

GRID PLATE PHONES

?FILAMENT

BATTERY

A typical grid -bias or power deociioncircuit. In slightly modified form. thisis 115,4 1 In the majority of modern broad -'as' receivers. In A.C. sets the "C"battery Is usually replaced by a biasingresistor connecbs1 in the plate returnlead.


ers, only the peaks of the impulsesregister. Since these peaks representthe original audio frequency modulationof the high frequency carrier wave, thediaphragm reproduces the sound of thetransmitted voice or music. Fig. 13gives an idea of the current transfor-mation, while Fig. 14 shows an ele-mentary grid bias detection circuit.

Grid Condenser Detection:

The second method of detection isknown as the grid condenser method,

lu the familiar giid-condenser systemof detection, a small fixed condenser isconnected in the grid lend of the tube,with a resistance of high value added ineither of the two positions shown.

and operates in an entirely differentmanner. In this system a small fixedcondenser is connected directly in thegrid lead, and the return side of thetutting circuit is brought to the positiveside of the "A" battery. A fixed re-sistance of high value is connectedeither across the grid condenser or be-tween the grid and the filament of thetube, as shown in Fig. 15. This givesthe grid a slight positive bias, and, ifthe correct value of plate potential ischosen, the tube then operates alongthe straight section of its characteris-tic curve.

With no signals being received, theplate current assumes a fixed value,depending, of course, on the filamenttemperature and the plate voltage.

When actual radio signals from abroadcasting station are tuned in bythe tuning circuit, an alternating volt-age corresponding to these signals isgenerated across the tuning condenserC, and naturally flows into the gridcircuit of the tube. During a half cyclewhen the grid is positive it acts likea little plate and attracts some elec-

trons to it. When the current changesits direction and the grid goes nega-tive, the electrons gathered by the gridjust an instant before find themselvestrapped in the insulated circuit consist-ing of the grid of the tube and thegrid side of the grid condenser. Onthe next half cycle, when the grid goespositive again, it attracts another littlebunch of electrons, and piles themup on the grid condenser along withthe previous batch. As the currentcontinues to flow, the grid condenseraccumulates more and more electrons,and these tend to make the grid moreand more negative in respect to thefilament. If they are left piling uplike this, they will eventually make thegrid so negative that it will cut offall the plate current, and the tube thenbecomes "choked" and inoperative.

Purpose of the Grid Leak:

The grid "leak" serves the purpose ofpreventing this undesired accumulation,by giving the entrapped electrons aconducting path to the positive fila-ment. Its value must be such that theelectrons have a chance to gather dur-ing a single wave train and then dis-charge in a group, so that the circuitis normal again when the next wavetrain comes along. If its resistance istoo low, the electrons will leak back tofilament as quickly as the positive gridattracts them; if it is too high, they

SIGNALPOTENTIAL

VARIATIONS°FORM

POTENTIAL -

CORRES-PCNOING

VARIATIONSOF PLATECURRENT

FINALMOVEMENT

OFREPRODUCER

DIAPHRAGM

IWAVEJTRAIN -1

MODULATED R.F. CURRENT

TIME DURING WHICH GRID CHARGELEAKS OFF

NORMAL VALUE OF PLATE CURRENT

FIG. 16

These curves show how the grid -conden-ser detector changes modulated radio-( r-quency signals Into audio currentsthat are capable of operating earphonesor other reproducers.


will not leak back quickly enough, andthe aforementioned blocking action oc-curs.

The manner in which this periodicaccumulation and discharge of gridelectrons effects a detecting action isillustrated graphically in Fig. 16. HereA represents the appearance of a car-rier wave modulated by an audio fre-quency current such as produced byvoice or music. B shows how the gridbias is depressed negatively from itsnormal slightly positive bias by thetrapping of the electrons, as described.C shows the corresponding reductionsin plate current, with the value return-ing to normal at the end of each wavetrain, when the accumulation of elec-trons is dissipated through the gridleak. As in the grid bias method of de-tection, the reproducer diaphragm doesnot respond to the individual littlebumps of current, because they are tak-ing place at the high carrier frequency.Instead, each wave train producesa single overall movement, and the neteffect of a continuous series of suchtrains is a reproduction of the originalprogram.

The wave patterns of actual speechor music are very much more compli-cated than the wave forms shown, butthese serve to illustrate the generalphenomenon.

Sometimes it is not necessary to pro-vide a grid leak in grid -condenser de-tectors. If the insulation between thegrid and the filament is slightly imper-fect, or if there is a tiny trace of gas

left in the tube, the grid charges willleak off automatically. However, inmost modern tubes both the insulationand the vacuum are so good that gridleaks are usually quite essential to thesuccessful operation of the circuit.

Comparison of Two Methods:

The grid -condenser method is moresensitive than the grid -bias method,because the accumulative effect of thewave train impulses produces a strongerchange in plate current, and also be-cause the tube operates on the straightsection of its curve and therefore am-plifies considerably as well as detects.However, the grid bias method, whilenot quite as sensitive, has the markedadvantage of superior power handlingcapacity. It will comfortably detect,without distortion, loud signals thatwould absolutely choke a grid con-denser detector. This is why practicallyall present-day broadcast receivers,which are built for high volume levels,employ grid bias detection in one formor another. In receivers that do nothave preliminary radio -frequencyamplification, the grid -condenser de-tector contributes an appreciableamount of sensitivity.

Audio Frequency Amplification:

If, after detection, the signals arenot loud enough, they can readily beamplified further, this time at audiofrequency, since all detectors produceonly the audio component of the sig-

Cb

RI

VI L V2 L

a

xCIA,

RIBX X

tO.

R2

V3 T1 V4 T2 V5 T3

X X

C6frp 9 g 410

Ri X x

0

GND

0B+90V 45 V.

Cb

R3

R4

Y Y

LOUDSPEAKER

FIG. 17

0B+

220V.

This typical tuned radio -frequency re-ceiver shows the uses of three -elementtubes as radio -frequency amplifiers. de-tector, and audio frequency amplifiers.The various "B" posts are intended forconnection to a "B" power pack. Fila-

ment leads "X" and "Y" run to a fila-ment light transformer. (Note: thiscircuit is shown only for purposes ofillustration; we do not have construc-tional data on ft.)


nal. One, two or three stages of audioamplification may follow the detector,the circuit being much like the radiofrequency amplifier except that differ-ent coupling transformers are used.

A complete radio receiver of typicalconstruction is shown diagrammaticallyin Fig. 17. This comprises two stagesof tuned radio -frequency amplification,(tubes V1 and V2 and tuning trans-formers and condensers L and C), agrid condenser detector (V3) and twostages of transformer coupled audio -frequency amplification (tubes V4 andV5 and transformers Tl, T2, and T3)Tubes V1, V2 and V4 may be the 227type, which have heated cathodes asthe electron emitters. The filaments,marked X, are all connected in parallelto a 21/2 -volt winding on a power trans-former. Tube V5 may be a 171A, whichuses raw a.c. on its filament. The leadsY run to a 5 -volt winding.

Obtaining Grid Bias:

Suitable grid bias for V1, V2 and V4is supplied by the voltage drop acrossthe fixed resistances R1, connected be-tween cathode and ground. The platecurrent of each tube runs through itsrespective resistor, so if the grid re-turn lead of each r.f. or a.f. transformeris brought to the bottom end of eachresistor, each grid will assume a nega-tive bias in relation to the cathodeequal to the voltage drop across theresistor. Since a 227 as an amplifierrequires six volts grid bias with 90 voltson the plate, and since the approximateplate current at this voltage is 3 mil-liamperes (.003 amperes), a simple cal-culation involving Ohm's Law will showthat R1 should be about 2000 ohms.The 171A tube, requiring 401/a volts

In the Triple -Twin tube, the cathodeof the first section is connected intern-ally to the grid of the second section.

grid bias at 180 volts plate, uses a sim-ilar biasing resistor R3, of about 2025ohms. Resistance R4 is simply a cen-ter -tapped resistance that provides azero reference point for the grid re-turn to the filament.

The Triple -Twin tube resembles an over-grown '45 -type. Notice how the two sec-tions are mounted on a common stem.

The various fixed condensers Cb areby-pass condensers to provide low im-pedance paths around the biasing re-sistors for the r.f. and a.f. currentspresent in the circuit.

Three -element tubes are made inmany different models for different ap-plications. The chart on page 30 liststhe types in present day use.

"Triple -Twin" Tube:

A novel tube consisting really of twocomplete triode assemblies in one glassenvelope was brought out a year ago.(Since then additional duo -triodes in asingle glass envelope have been de-


veloped and are available, such as types53 and 79.) However, this tube is veryinteresting and worth mentioning.

The tube looks like an overgrown224, as it has a cap electrode at thetop. Inside, mounted on a single glassstem, are the approximate elements ofa 227 general purpose tube and a 245power output tube, with the cathode ofthe former connected directly to the

A.FINPUT

A

INPUTSECTION

Cl

IRI

R2

I OUTPUTI SECTION

0

OUTPUTTRANS.

4

fLOUD

SPEAKER

HEATERsime

/0159 SECONDARYON POWER

TRANS.

FIG. 17 B B - B-i-

How the Triple -Twin is used as a com-plete audio amplifier In itself. The cir-cuit is rather unusual and requirescareful study and consideration.

grid of the latter, as shown in Fig.17A. There is no external connectionfor this grid.

Known as the "Triple -Twin" tube thisunit is virtually a complete direct cou-pled audio amplifier by itself, or a com-bination detector and amplifier. The

input tube operates in the usual man-ner as a detector or amplifier, but theoutput tube utilizes the positive regionof the grid voltage -plate current curve.The manufacturers claim this methodproduces a relatively high undistortedpower output independent of arid cur-rent flow.

An amplifier circuit employing theTriple -Twin tube is shown in Fig. 17B.The input section is normal except thatthe cathode is above ground potential,and this means that the applied signalvoltage is likewise above ground poten-tial. The signal reaches the cathodethrough condenser Cl, of low imped-ance. The grid of the input tube isproperly biased negatively by resistorR2, the d.c. return path to the arid be-ing through resistance Rg. The in-ductance 1.1 allows a low resistance d.c.path for the grid and plate returns.Resistance R1 establishes the grid ofthe output section a few volts negativeand is only necessary in a.c. operationto suppress hum. Notice that the gridof the output section receives its bias,and also its energizing signal, from thecathode of the first section.

The action of the circuit combinationis rather complicated and a full explana-tion of it is beyond the scope of anelementary manual. The output tubeacts as a regular triode, but it is builtin a special manner to provide self -com-pensation for the flow of grid currentwhen the signal swings the grid posi-tive.

CHAPTER 4Vacuum Tube Characteristics

The study of vacuum tube character.istics is usually so confused by com-plicated mathematics that the averagestudent is likely to become discouragedwhen he attempts to learn somethingabout the subject. While a knowledgeof advanced mathematics is exceeding-ly useful here, as it is in all phases ofelectricity, a practical understanding oftube operation can be achieved withoutrecourse to trigonometry.

Amplification Factor:

The amplification factor of a tubehas already been defined as the ratioof change in plate voltage required tochange the plate current a certainamount to the change in grid voltagethat produces the same variation.

The amplification factor of a tubedepends to a large extent on its mechan-ical construction. It increases as thegrid wires are brought closer together,thus increasing its effective area andgiving this electrode greater controllingpower over the electrons passingthrough it. It also increases as theratio between the plate -filament and thegrid -filament distances increases, as thecloser the grid to the filament (in com-parison to the plate), the more effec-tively will a small voltage on it retardor aid the electron bombardment of theplate.

The amplification factor of ordinarythree -element tubes does not exceed 10,although mu's of two or three hundredhave been obtained in special experi-mental tubes having the grid very closeto the filament. Changing the mechan-ical inter -relation of the three elementschanges other characteristics besidesthe amplification factor, and this mustalways be taken into consideration.

Close spacing of elements makes theassembly operations very difficult, andusually results in lack of uniformityin quantity production. Close spacingalso makes a tube very sensitive tomechanical vibration, which manifests

itself as a "microphonic" howling orringing sound. In some sets the tubesare fitted with heavy metal or rubbercaps to weight them down and preventthem from vibrating in sympathy witha nearby loud speaker.

The amplification factor of a tube isnot a definitely fixed value, but variesslightly with the applied grid and platevoltages.

Plate Impedance:

Plate impedance is the second im-portant characteristic of a tube. Thismay be understood from the funda-mental action of three -electrode tubes,as already explained. When the plateis made positive in relation to the fila-ment, a current of electricity flowsthrough the battery circuit and alsothrough the space between the plate andthe filament inside the bulb. The actualamount of current for a given filamenttemperature depends on the grid biasor potential, as well as on the platepotential. The tube can thus be con-sidered as a variable resistance. Thelower the grid bias, the higher the platecircuit resistance; and the higher thebias (in a positive sense) the lower theplate resistance and therefore thegreater the plate current. This resist-ance is known as the "internal resist-ance" of the tube.

The combination of the straight in-ternal resistance of a tube and thereactance offered by the small con-denser formed by the plate and thegrid is the impedance of that tube. Inmost tubes this capacity effect of theelectrodes is very slight and is notice-able only at very high frequencies.Therefore, for all practical purposes theinternal resistance of the tube in ohmsis taken as the plate impedance. Moreaccurately, plate impedance may be de-fined as the change in plate potentialin volts divided by the change in platecurrent in amperes that it produces. Ofcourse the value will be different for

17


different grid and plate voltages, butit is usually measured at the normalvoltages used for radio set operation.

Mutual Conductance:

The third important tube constant tobe considered is mutual conductance, or"transconductance," as it is now knownin engineering circles. The primarypurpose of an amplifier tube is to pro-duce a large undistorted change in platecurrent for a small change in grid volt-age. As this action depends on theratio of the change in grid voltage tothe corresponding change in plate cur-rent, by comparing these values we ar-rive at a value which is then known asthe "mutual conductance." This is amathematical ratio which takes into ac-count both the amplification factor andthe plate impedance, and is thereforea measure of the operating efficiency ofthe tube. It is equal to the amplifica-tion constant divided by the plate im-pedance, the resulting quantity beingexpressed in "mhos." The unit "mho"is the "ohm" spelled backwards, the"conductance" of a material being thereciprocal of its "resistance."

As a general rule, a tube with a highmutual conductance is the best one foramplifying purposes, but of course otherconsiderations such as current consump-tion, inter -electrode capacity, etc., mayalso influence the selection of tubes forcertain applications.

The relation between amplificationfactor and mutual conductance is boundto be confusing at first, but becomesclearer after the student has studiedthe factors carefully and is able to seethe difference between the voltage andcurrent variations and their connectedeffects.

Power Tubes:

The amplification factor indicates onlya tube's voltage amplifying characteris-tic, and tells nothing about its powerhandling capacity. A tube that is usedin the last audio amplifier stage of areceiver must deliver actual power to

a loud speaker, so that the diaphragmof that instrument may vibrate, set airinto motion and reproduce sound. Sucha tube should have a low plate imped-ance, so that the power supplied to theplate circuit will not be wasted inmerely overcoming the plate resistance.Most power tubes have this desirablelow impedance, but they also have lowamplification factors. They must bepreceded by one or two amplifier stagesusing higher mu tubes in order thattheir full output may be realized.

Mechanically, output tubes differfrom general purpose tithes like the 227in that their filaments, grids and platesare larger and heavier. Since they areused only for audio amplification, thegrid -to -plate capacity is of little im-portance. The plates are usually black-ened to aid heat dissipation and reducesecondary emission, and the insulationbetween the elements is made extraLeavy to avoid breakdown under thehigh voltages used. Power tubes getvery hot in normal operation becauseof the terrific electron bombardment ofthe plate, and cannot be touched withthe fingers after they have been work-ing for more than ten minutes or so.In some of the larger power tubes usedfor transmitting work it is not uncom-mon for the plates to glow at a dullred or even a white heat. Such tubesrequire considerable ventilation. Tubesdesigned to handle powers of five kilo-watts or more are provided with cool-ing jackets through which cold watermust be kept flowing constantly to pre-vent the elements from melting.

In the "power" class are such tubesas the 112A, 171A, 245, 210, 250, and231. Power pentodes are described inthe next chapter. Among the transmit-ting tubes of the three -electrode typeare the following: the 203A, rated at75 watts output with 1000 volts on theplate; the 211, with a similar rating;the 852, 75 watts with 2000 volts on theplate; the 204A, 250 watts output with2000 volts plate; and the 849, 350 wattswith 200 volts plate. These are rarelyencountered by the average radio man,being used only at amateur and com-mercial transmitting stations.

CHAPTER 5

Four- and Five -Element Tubes

Space Charge Effects:

The major limiting factor in the am-plifying action of three -element tubesis the space charge. This has two un-desirable effects: (1) it constantly op-poses the attractive effect of the posi-tively charged plate on the electrons;(2) it lowers the amplification factor,since the grid does not have completecontrol of the electrons flowing throughit.

The space charge can be overcomeor reduced considerably by the intro-duction of a positive charge in the tubenear the region where it accumulatesby simply adding a fourth electrode tothe tube which is given a positivecharge just like the plate. This newelectrode may be placed between thefilament and the grid, or between thegrid and the plate, and of course mustbe of open construction, like the grid,so as to let the electrons fly through it.

"Space Charge" Tube:

If the second grid is placed betweenthe filament and the present controlgrid, the new tube thus formed is call-ed a "space charge" grid tube, and hasa greatly increased amplificationfac-tor, slightly increased plate impedanceand about the same grid -to -plate capac-ity as before. See Fig. 18.

"Screen Grid" Tube:

If the second grid is placed betweenthe grid and the plate, the tube is called

In the space -charge tetrode, the secondgrid is located between the filament andthe regular control grid.

a "screen -grid" tube. See Fig. 19.n this position also it helps to break

up the space charge, increases the effec-tiveness of the grid control, and there.fore raises the amplification constant.It also has another very important ef-fect, and that is a marked reductionin the capacity between the present con-trol grid and the plate. The screenacts as the common plate of Iwo smallfixed condensers in series, the grid andthe plate acting as the other plates. Thetwo condensers being in series, the re-sultant capacity between the controlgrid and the plate is smaller than thecapacity of either of the two condensersalone. In an ordinary 201A three -ele-ment tube the grid -to -plate capacity issomething like 10 micromicrofarads; inthe 222 screen -grid tube it is onlyabout .025 micromicrofarad. That'squite a difference.

Importance of the Low Tube Capacity:

The great significance of this reduc-tion of grid -to -plate capacity can be un-dcrstood from a brief consideration ofradio -frequency amplifier design. InFig. 20 we have a typical tuned radio -frequency amplifier using three -elementtubes. The capacity effect between thegrid and plate elements is representedby the small fixed condensers C. Weakradio signals picked up by the antennaand tuned in by the tuning circuit LC1have a choice of two paths: (1) thegrid -filament circuit, in which they op-erate the grid properly and cause them -

In the screen -grid tetrode, the secondgrid is situated between the control gridand the plate.

19


selves to be amplified by the tube; (2)the condenser C. Naturally any currentthat goes through C is not amplified bythe tube, which loses just that mucheffectiveness.

The axed condensers C represent thegrid -to -plate capacity of ordinary three -element tubes. this capacity effect be-CMIlles very serious as the frequency ofthe radio signals goes up (as the wave-length goes down).

The extent of the by-passing of Cdf pends on its own capacity in relationto the wavelength or frequency of thesignal current. Since the reactance ofa condenser varies inversely with thefrequency of the current applied to it,the reactance of C will become lowerand more current will pass through itas the signal frequency goes up (wave-length goes down).

The capacity C also provides a me-dium for the feed -back of energy fromthe plate circuit to the grid circuit,resulting in uncontrollable oscillation,heterodyne whistling, distortion andfurther loss of amplification. In earlytuned r.f. amplifiers it was necessary toovercome these bad effects by "neutral-izing" the tube capacity by variouscomplicated methods, which at best al-lowed the circuits to realize only atraction of the full amplification ofwhich the tubes were capable.

This capacity effect, by the way, ex-plains why some radio receivers seemto work just as well with the r.f. tubesturned off. The capacity exists all thetime by virtue of the mere mechanicaljuxtaposition of the grid and the plate.Whether the filament is lighted or notmakes no difference.

Since the grid -to -plate capacity ofthe screen -grid tube is comparativelysmall, no neutralizing of any kind isneeded even on a wavelength as low as5 meters, whereas with three -electrodetubes such neutralization is necessaryeven on 400 meters. The screen -gridtube has found widespread use as aradio -frequency amplifier for this rea-

son. It is also an excellent detector,operating on the grid condenser meth-ods.

Comparatively little use is made ofthe space -charge tube, except as anaudio amplifier in some special circuits.The main advantage of the second gridis in making the tube a better radio -frequency amplifier. Incidentally, anyscreen -grid tube can be used as a space-cuarge tube if the present control gridis given a positive charge and the screengrid then operated with a negative biasas the control grid.

In its commercial form the screen -grid tube uses either a filament, forbattery operation, or a heated cathode,fcr a.c. operation, and the second gridor screen takes the shape of a doubleelement completely surrounding theplate. See Fig. 21. The connection forcontrol grid is brought out to a cap onthe top of the glass bulb, so as to mini-mize the capacity effect between it andthe connections of the other elements.

The usual grid pin in the base is thescreen -grid terminal.

The voltage applied to the screen isusually a fraction of that applied to theplate. Since the screen acts like a plateand attracts electrons, there is a screencurrent, but this is very small becausethe screen is of open construction andpresents only a limited surface. Be-sides, the electrons broken out of thespace charge by the screen are attract-ed through the screen by the muchhigher positive charge on the plate.

Among the tubes in the screen -grid

Relative location of the elements in anactual commercial screen -grid tube. Thescreen element completely surrounds theplate. thus shielding it thoroughly fromthe control grid.

class are the following: the 222, whichwas the first four -electrode tube on theAmerican market, and is now more orless obsolete; the 224, of the heatedcathode type, for use on a.c.; the 232,


a two -volt battery tube with a regularfilament; and the 23t, a battery typetube using a heated cathode instead of afilament. The 224A has recently re-placed the 224, from which it differsonly in that its cathode heats to oper-ating temperature more quickly.

Variable -Mu Tube:

One of the disadvantages of the 224screen grid tube is its inability to han-dle strong signals. Its characteristicgrid voltage -plate current curve is verysteep, and if the signal is very strongit is likely to swing the plate currentdev. n to the bend of the "knee," result.ing in grid -bias detection, and subse-quent distortion on one half of the cur-rent cycle. Interference from neighbor-ing stations sometimes also causes"cross -talk" on a desired station be-cause of this same effect.

The trouble has been largely over-come by the introduction of a new typeof screen -grid tube known as the "var-iable mu," in which either the controlgrid or the screen -grid is of somewhatuneven construction and gives the tubea varying amplification constant or muas incoming signals necessitate makingthe control grid more and more nega-tive. With weak or medium signals thetube has the same mu as a regular 224,but with stronger signals that wouldoverload a 224 the amplification factordrops automatically and the tube re-mains operating on a straight sectionof its grid voltage -plate current curve.As long as the operating point is on astraight section no detecting action cantake place and the signal is amplifiedjust as it should be.

Two types of variable mu tubes havebeen introduced, the 551 and the 235.

'These curves rhoµ the difference Incharacteristics between the regular '3-1screen -grid tube and the special ':t5 va-riable -tau type. Note t he gradual slopeand wider grid voltage range of latter.

The 551 is much like the 224 and canINo substituted for it with only a slightchange in the grid bias; its range ofcontrol grid bias is more than twicethat of the 224. The 235 has more thandouble the plate current of the 224 andonly about half the plate resistance,which makes greater amplification perstage practical. It is not interchange-able with the 224, but in new sets it isreplacing it almost entirely for ampli-fication purposes. The "tailing" of thecharacteristic curve of the 235 and 551wakes these tubes poor grid bias de-tectors, the 224, with its more abruptbend, being much better. An idea ofthe comparative curvatures of the 224and 235 characteristics may be obtainedfrom Fig. 22.

Power Pentode:

The power output of the four -elementtube or tetrode is limited by a factorknown as secondary emission, whichwas mentioned in Chapter 1. With theelectron stream to the plate strengthen-ed and accelerated by the breaking upof the space charge by the screen gridelectrode, the bombardment becomes soheavy that the surface of the plate it-stlf begins shooting off electrons. Ifthe plate voltage is low the plate doesnot have sufficient attraction to pullthem back, and they fly instead to thepositively charged screen -grid, at thestme time repelling other electronsaway from the plate and causing a dropin plate current. This dip is illustratedby curve 1 of Fig. 22A, which showsthe relation of plate voltage to platecurrent in a typical four -electrode tube.

To prevent the secondary electrons

61 /lode, two electrodes: triode. three elec-trodes : t ru0e, four electrodes; pentode,live cI, 11,sles.

The dip in the plate -voltage, plate cur-rent curve of screen -grid tubes Is due10 the secondary emission effect of theplate. This dip is eliminated in the-pentode" by the third grid element.


from aiding the space charge, a fifthelement in the form of a third grid isadded to the tube, between the pre-sent screen grid and the plate. Thisis connected back to the center of thefilament, which, being at ground poten-tial, prevents the loose electrons frompassing further. The connection ismade inside the tube, as shown in Fig.V. The third or "suppressor" grid re-moves the plate current dip, as shownin curve 2 of Fig. 22A.

rra tigenien Of the elect roles in thepentode. The third grid, known as the"suppressor grid." is connected intern-ally to the center of the filament, andhas no external terminal.

This five -element tube, or "pentode",is a veryfication. In comparison with a triodeof the same plate dissipation or power,it is capable of producing greater poweroutput with less signal input. It hasboth high amplification factor andpower capacity, which neither the triodenor the tetrode has by itself. A powerpentode may be connected directly aftera detector tube without the usual firststage of amplification, and will furnishplenty of volume for loud speaker oper-ation. It is most valuable in receiversin which space is limited, since it elim-inates one tube and its associated equip-ment.

Pentodes are now available for 2 -voltand 6 -volt battery service and for alter-nating current. The 233, the 2 -volttube, and the 247, the a.c. tube, usefilaments as the electron emitters; the238, one of the so-called "automobile"tubes, uses a heated cathode.

R.F. Pentode:

A suppressor grid may be added to aregular screen -grid amplifier tube toproduce advantages similar to those

obtained in the audio power tubes. Thishas been done in the new 239 tube,which belongs in the 6.3 volt "auto"family and has been designed especiallyfor operation on low plate voltages. Itcombines the variable mu and the pen-tode features, and has particularly highmutual conductance. As in the 235tube, the variable mu action is obtainedby a control grid having uneven pitchor spacing between turns.

The advantages of the 239 over the236, which it is intended to replace, aregreater output for the same input, bet-ter control of volume on strong signals.and elimination of cross talk interfer-ence. As this tube is extensively usedin power AF stages of battery and autoradio receivers, characteristic data isherewith given; more complete data willbe found in the charts beginning onpage 30.

Type 239

Variable -Mu R.F. Pentode

Purpose: radio -frequency amplifierBase: UYDimensions: 41-4" long, 11V in diameterCathode Type: HeaterCathode Rating: 6.3 volts, 0.3 ampere,

D.C.

Plate Voltage: 90 to 135 (180 maximum)Screen Voltage: 90Control Grid Bias: 3 voltsPlate Current: 4.5 milliamperesScreen Current: 1.7 milliamperesPlate Impedance: 300,000 to 680,000

ohmsAmplification Factor: 285 to 700Mutual Conductance: 950 to 1050 mi-

cromhosMutual Conductance at 40 volts control

grid bias: 1 micromho.

Screen Grid Transmitting Tubes:

There are three screen -tubes in thetransmitting class, finding use mostlyin short-wave stations because of theirlow inter -electrode capacity. These arethe 865, having an output of 71/2 watts;the 860, rated at 75 watts; and the 861,rated at 500 watts.

CHAPTER 6

Light -Sensitive Cells and Other Special Tubes

Photoelectric Cell:

For many duties in industry the hu-man eye is being replaced by an inde-fatiguable electric eye-the photoelec-tric cell. Wide application has beenmade of this remarkable device, par-ticularly in television and talking mo-tion pictures, for counting objects pass-ing a fixed point, detecting smoke, con-trolling illumination, and countlessother purposes.

Light-sensitive cells have been knownfor a long time, but only recently havethey achieved any widespread commer-cial use. Their application was form-erly limited by their fragility and gen-eral unreliability, but they have beenso greatly improved during the lastthree or four years that they are noweAtirely reliable. Because they are in-variably used in conjunction with ordi-nary vacuum tube, and properly belongin the vacuum tube family, their theoryand operation should be understood byevery radio man.

A photoelectric cell is a light-sensi-tive device which, when connected to acircuit of proper voltage, permits acurrent to flow only when the cell isilluminated by a suitable source. Thetypical photoelectric cell, as shown inFig. 24, is quite simple in construction,consisting merely of an anode and acathode sealed in an evacuated bulb,

The photo -electric cell is a very simpledevice, consisting merely of a cathodecoated with a light-sensitive material,and an anode to attract the liberatedelectrons. In some types, the cathode isa metallic deposit on the inside of theglass bulb.

or in one filled with gas at a low pres-sure. The cathode is a metal platecoated with a material that has theproperty of emitting electrons whenlight falls on it, while the anode is abare conducting wire. An alkali metallike sodium, potassium, rubidium orcaesium is used to form the sensitivecathode surface. In some cells thelight sensitive coating is deposited onthe inside of the glass containing bulb.

hi, circuit of the photo -electric cell Isvery similar to that of the two -elementrectifier. The anode is made positive toaccelerate and attract the electrons fromthe ea t bode.

Caesium is commonly used at presentbecause it is more sensitive to the redend of the color spectrum than theother alkalis.

The operation of the cell may easilybe understood from Fig. 25, whichshows a simple photoelectric cell cir-cuit. When light falls on the cell, thecathode liberates some electrons, justas the filament of an ordinary radiotube does. Since the plate is chargedpositively by a battery, it will acceler-ate and attract the electrons, and themeter will indicate a current flow, cor-responding to the plate current of aradio tube. The stronger the light thegreater the electron emission and thehigher the current flow.

There are two general types of photo-electric cells: vacuum and gas filled.In the vacuum type, the glass bulb isevacuated as thoroughly as possible, andthe current flow between cathode andanode is due purely to the electronsfreed from the cathode surface. In thesecond type, the tube is filled with agas at a low pressure. The maximum

23


current which can flow is much greaterthan that represented by the electronemission alone, for ionization by col-lision takes place (See Chapter 2). Thepresence of the gas increases the cur-rent flow as much as ten times.

There are many variables in photo-electric cell structure which affect thecharacteristics. Briefly, they are: (1)the kind of light sensitive material:(2) the process of manufacture; and(3) the kind of gas and its pressure.The final characteristics of a cell dpend on the combination of these fac-tors as arranged by the designer. Cellscan be made sensitive only to certainsections of the light spectrum, for spe-cial purposes. Some cells respond onlyto ultra violet or infra -red. The major-ity of cells are designed to respond tolight in the visible region of the spec-trum and hence are the most suitablefor most applications.

The response of a photoelectric cellto variations of light falling on it isinstantaneous, the electron stream be-ing without appreciable inertia.

Even in the most sensitive photo-electric cells the current flow isingly small, possibly only a few micro-amperes. To make the current varia-tions useful, they must be amplifiedconsiderably. Ordinarily multi - stageaudio -frequency amplifiers are employ-ed for this purpose when all the finegraduations of light must be translatedinto electrical energy, as in televisionsystems. For many industrial purposesa special type of amplifier known asthe "grid glow" tube is used. Thisdiffers from standard amplifiers in thatit operates only when the illuminationon the photoelectric cell, and hence thecontrolling current, reaches or dropsbelow a certain point. Such a tube isvirtually an electronic relay and is usedto control power circuits and the like.An example of the application of aphotoelectric cell and grid -glow tubecombination is a factory or street light-ing control system, wherein overheadlights are turned on as the naturallights grow dim, or are turned off asthe daylight becomes brighter.

New applications for the photoelec-tric cell spring up daily. The follow-ing are only a few: sorting of cigars,beans, eggs, and various other kindsof foodstuffs according to color; count-

ing of automobiles or pedestrians pasta fixed point; recording of smoke den-sity; control of baking or roasting pro-cesses; recording the thickness ofvarious materials such as paper, wire,etc.

Other Light -Sensitive Cells:

There are other light-sensitive de-vices, such as the selenium tube andthe electrolytic cell, but these are notas flexible as photoelectric cells and arerarely used except for laboratory exper-iments. Selenium is a material thatchanges in resistance when a light fallson it, just as a telephone transmitterchanges in resistance when sound wavesimpinge on it. It is sluggish in actionand not at all as dependable as vacuumtubes. The electrolytic cell, employ-ing a light-sensitive liquid solution,has obvious mechanical disadvantages.

Neon Tube:

For the reproduction of televisionimages, a device known as the neonglow tube is used. This consists of twoflat metal plates mounted parallel toeach other and about inch apart,inside a glass bulb filled with neon gas.See Fig. 26. When connected in a di -

The noon tube used for television recep-tion consists !merely of two flat metalplates, separatist a short distance in abulb filled with neon gas.

rect current circuit a reddish pink glow,characteristic of the gas neon, coversthe entire surface of one of the plates.The usual neon tubes employed in tele-vsion receivers glow properly at about135 volts, passing about 15 milliam-peres. Their plates are about M."square.

The neon tube is connected in theplate circuit of the last audio tube of


the television receiver, just like a loudspeaker. See Fig. 27. It is kept il-luminated by the direct plate current,but flickers in accordance with the var-iations of the television signals. Thescanning disc, rotating in front of thebulb (in a plane parallel to the plates),reconstructs the transmitted image. Itshould be clearly understood that whilethe flickering takes place over the en-tire surface of the plates, only a tinysection at a time is exposed to viewby the holes in the scanning disc.

The 111.4111 tube is conneeied in the platecircuit of the last amplifier tube justlike a loud speaker. It is illuminatedby the normal plate current of the tube,to whbli II must be matched carefullyfor proper operation.

Neon tubes are used for televisionwork because, like other radio tubes,they have no appreciable time lag andrespond instantly to any changes ofcurrent through them. Ordinary elec-tric lights have a much greater bril-liancy, but there is no simple means ofmodulating them at audio frequencies.Considerable research work is beingdone on television glow lamps, as noneof the available types are entirely sat-isfactory.

Other Special Tubes:

The "phanotron" is a gas vapor con-tent vacuum tube. The name appliesto gas or vapor tubes regardless of thenumber of electrodes or their nature.In practice it most often indicates atwo -element rectifier. The "thyratron,"which has recently been put to consider-able industrial use, is a phanotronwith three electrodes, a filament orother electron emitter. a grid and a'date. The word "thyratron" is derivedfrom the Greek term meaning "door,"and this tube is essentially a grid con-trolled arc rectifier.

A phanotron rectifier consists of twoelectrodes, an anode (or plate) and acathode, mounted in an exhausted con-

tainer in which there is a partial at-mosphere of inert gas or vapor. Thepartial atmosphere is usually the vaporpressure of a quantity of mercury, al-though it is sometimes a gas like ar-gon, neon or helium.

As explained in Chapters 1 and 2,iu a high vacuum tube the current islimited by the supply of electrons emit-ted by the cathode, and by the electronspace charge around the cathode. Inthe phanotron the cathode supplies theelectron flow, but the space charge isneutralized by the ionization of thevapor or gas. (The ionization by col-lision effect, once more.) This resultsin a low voltage drop across the tube-only about 15 volts for mercury vapor-which is practically independentof current. Therefore a phanotron canrectify and carry much heavier currentsthan a high vacuum tube of correspond-ing dimensions.

An experimental type of mercuryvapor rectifier intended to replace thestandard high vacuum 280 has beenreleased by at least one tube manufac-turer. When substituted for a 280 inan existing power pack the output volt-ages are higher and the current carry -in capacity considerably greater.

The Thyratron:The thyratron is a phanotron with a

grid control. This apparently makesthe tube a regular triode, but the ac-tion of the thyratron grid is quite dif-ferent from that of the triode grid.The grid controls only the starting ofthe internal discharge. After starting,it cannot modulate, limit or extinguishit, as can the grid of an ordinary tri-ode. The ionization of the gas vapornot only overcomes the space charge,but also tends to neutralize the con-trolling charge on the grid. To allowthe grid to regain control after theplate current has started to flow, a pro-hibitive grid charge is required. Theplate voltage must be reduced to prac-tically zero or made negative enoughfor the gas or vapor to become deion-ized. Once this deionization takes placethe grid resumes control.

It alternating current is applied tothe plate, the grid has an opportunityto regain control once during eachcycle, and can delay the starting of the


arc for as long a period during thesubsequent positive half cycle as thegrid voltage is sufficiently negative.This means that the grid can controlthe average current flowing throughthe tube and that this averaging canbe made as "fine grained" as desiredby increasing the frequency of inter-ruption.

If the grid as well as the plate Issupplied with alternating current, thephase relation between the grid and theplate naturally determines the amountof average current flowing through thetube.

The voltage conditions for startingthe current depend largely on the struc-tural design of the tube. A tube maybe designed so that within the normalplate voltage limits the current alwaysstarts at a negative grid voltage, oralways at a positive grid voltage, or ata negative voltage for high plate volt-ages and a positive voltage for lowplate voltages. The ability of the tubeto directly control large amounts of cur-rent without intermediate mechanicaldevices makes it extremely valuable fora variety of purposes.

Thyratron Inverter:

One of the most interesting uses ofthe thyratron is for the conversion ofdirect current into alternating current-just the reverse of its normal func-tion. Direct current is applied to theplates and the grids are supplied withthe desired frequency, either by an ex-ternal exciter or by means of couplingto the output circuit. In this respectthe thyratron inverter may be consider-ed as an amplifier or an oscillator, re-spectively. The function of the tubesis to commutate, or perform a switch-ing operation. In all inverters someform of power storage is necessary inorder to supply power during the com-mutation period. This may be in the

form of static condensers, a power sys-tem or in rotating apparatus.

The fundamental action of thyratroninverters may be illustrated by the sim-ple single phase arrangement of Fig.28. The plates of both tubes are posi-tive. Assume that the grid of the up-per tube is positive. Current will flowfrom the positive d.c. source throughthe transformer to the negative d.c.line by way of this tube. The grid ofthe lower tube is negative and allowsno current to pass. The condenser ischarged with the potential drop acrossthe output transformer due to the cur -

This odd circuit shows how thyratraniinics are used to convert direct currentint., alternating current.

rent flow in the upper half of the wind-ing, the upper terminal becoming neg-ative and the lower positive. Towardthe end of the cycle the grids exchangepolarity. This has no direct effect onthe current flow through the first tube,but allows current to flow through thesecond, which in effect connects thelower side of the condenser to the nega-tive lead. This places a negative volt-age of short duration on the upperplate, allowing the upper grid to regaincontrol.

A number of types of thyratron tubeshave been developed. They range incurrent capacity from 1 to 75 amperesand in voltage from 1000 to 20,000.A special tube capable of passing sev-eral hundred amperes has been made.This stands almost three feet high!

MODERN VACUUM TUBES

Special OverheadOverhead Heater Tube:

In all standard American receivingtubes the filament or heater connectionsare made through two of the pins inthe base. Several years ago, however,an a.c. tube having the heater connec-tions to a separate cap on the top ofthe glass achieved considerable popu-larity, and is still being used in manybroadcast receivers. The appearance ofthis "overhead heater" tube is shownin the accompanying illustration. A

special double -contact cap snaps overthe top of the tube, the various caps ina set being joined by a flexible cable.

As the overhead heater tubes havecharacteristics different from those ofstandard tubes, the following chartsshould be consulted if the reader en-counters the tubes in service work.

Service Men who encounter receiver,using these tubes should take particu-lar note of their filament voltage, whichis three volts. Do not attempt to re-place them by tubes of the 227 typeunless you reduce the filament voltagewills series resistors.

Average Characteristics Type 401General Purpose Defector, Radio and Audio

amplifier Tubem.o., voltage -3.0 volts. Heater current -1.0 amp.

Heater Tubes

-1-1(ELL0GO

TYPE 403A -C TUBE

Average Characteristics Type 403Power Amplifier for Last Audio Stage

Maw voltage -3.0 volts. Heater current -1.5 amiss.

27

Plate voltage 151 90 111 180

Negative grid bias 0 4.5 6.0 7.5 9 0 10 6 12 0 Plate voltage 135 180l'Iate current

(milliamperes)/Mato impedance

(olints1

3.8

9060

3.7

10750

2 5

13300

5.3

9520

3 9

11700

7.2

0330

5 8 Negative grid bias10100 Plate current (milliamperes)

Plate impedance (ohms)

2715

2500

5020

2500Amplification factor 10 0 10.0 10.0 10.0 10 0 10.0 10 0 Amplification factor 3.0 3 0Mutual ,- luctance

(Micromboar 1100 930 710 1050 850 1070 932 Mutual conductance (micromlios) 1200 1200Power output} Power output' (milliwat1.) 360 (,60

(milliwalfia 20 26 67 73 137 166

°For use as detectordetection.

}Tim value, given for rut Itatt represent tentlistorterl output nrOutput of negligible distortion. Tliese values arm far optitnuttoload regialance or a load restiotarice of approximately twice thetube idIpPgilallee.

.112 using grid leak and condenserThe values given for output represent undistorted output nr

outpot of negligible distortion. The.se values urn far optimumload resistance or a lad resistance el approximately twice thetube impedance.

Filament Resistor Values for Two -Volt TubesFiord R imam Valuer for Two Volt Filament Tutus

Number Tom Dm Cell. (1.0V.) Two Edison Cell. (RSV.)of CX.I30sor lac -flex. 1

CX-5112

CX-11141

'a-3ft2

CX4331%

1 4.2 ohm 21 ohou 5.2 ohm. 1.11olum2 5.2 2.1 2.4 " 141 2.6 1.1 1.9 ° 1.4

4 2.2 " 1.6 " 1.6 " 1.2

5 1.9 " U 14 ° LI6. 1.6 " 1.1 " 1.0

7 1.5 0 1.2 " 1.o 09 '

Nun 546 $$$ i $$ ance are needed gybe. taw ng elr-616 cal seamy hmory

Mammas Velem for Toe Volt Filament Tuber-(Mioismn)

Numberof CX.SIONft C3C.332'.

Toe Dry Cello (1.09.) Two Edimm Cello (UN.)

ICX-111

2CC -l11'

ICZ -111

2cx-iir.

6 ohm. Soh= 5 ohms 1 ohms

) " 1 4 154 " "3 1 . 2

5 " 2 2.1 " 1.1

1 2 2 " 1.1

2.5 2 1.1 132 13 " 1.1 15

2S MODERN VACUUM TUBES

"Exploded" Views of 2- and 3 -Element TubesGLASS ENVELOPE

FILAMENT SHEETMETAL

ORMESHPLATE

FILAMENTSUPPORT

PLATESUPPORT

BASE

PINSF

GLASSSTEM

CONNECTIONWIRES

TO PINS

" DIODE"TWO

ELEMENTTUBE

commonest form of the diode ortwo -element tube is the 281 half -waverectifier. tither diodes, built on a smallerscale, are used for detecting purposes.

GLASS ENVELOPE

FILAMENTSUPPORT

GRID

PLATE

FILAMENT

PLATESUPPORT

CONNECTIONWIRESTO PINS

BASE

TRIODE"FILAMENT

TYPEPINS

F

The triode or three -element tube isradio's "Jack of all trades"; amplifier,detector and oscillator. In this class arethe 1121. 120, 1711, 2011, 226, 230,245, etc.

FILAMENT

PLATE

GLASS.SEEM -

BASE

PINS

GLASS ENVELOPE

F

FILAMENTSUPPORT

FILAMENT

PLATE

CONN ECTIONWIRES

TO PINS

DOUBLEDIODE -

(REcriFIER.FULL -WAVE )

The double diode consists simply of twosets of diode elements. The 2M) is themost familiar lithe of this type. Similartubes are used for detection in some spe-cial super -heterodynes.

GLASS ENVELOPE

GRID

Fl LAMENTHEATER

GLASSSTEM

BASE

PINS

PLATE

CATHODE.

CONNECTIONWIRES

TO PINS

TRIODE"(HEATER)

TYPE /

The triode with a heated cathode is thewell-known 227. For purposes of heatradiation the plate in some makes isclose mesh instead of sheet metal. Noticethe filament inside the cathode.

MODERN VACUUM TUBES

"Exploded" Views of 3- ands- Element Tubes

GLASS ENVELOPE

FILAMENT(INSIDE CONTROL

GRID)

GLASSSTEM

BASE

PINS

F

CONTROL -GRIDCAP

CONTROLGRID

SCREEN GRID

PLATE

CONNECTIONWIRES TO

PINS

TETRODE"(FILAMENT

TYPE)

The tetrode or four -element (screen -gridtube has two grids in addition to thefilatnent nod plate. Note that the screen -grid completely encircles the plate. The222 and 232 are in this class.

CONTROLGRID

CATHODEGRID

GLASSSTEM

BASE

PINS

GLASS ENVELOPE

6

SCREENGRID

FILAMENT

CONNECTIONWIRES TO

PINS

PENTODE"(A.F.TYPE WITH

FILAMENT.)

The pentode or five -element tube hasthree grids. The cathode or suppressorgrid, located between the screen grid andthe plate, is connected internally to thecenter of the filament.

29

GLASS ENVELOPE

FILAMENT

PLATE

CATHODE

GLASSSTEM

BASE

PINS

_5-- CONTROL -GRID

CAP

P

SPECIAL GRIDIN VARIABLE -

MU TYPE

SCREEN GRID

CONNECTIONWIRES TO

PINS

"TETRODE"( HEATER

TYPE'

The tetrode with a heated cathode isthe popular 224 screen -grid tube. Anidentical construction is used in the 236.In the 235 variable -mu type the controlgrid has uneven pitch, as shown.

The neon tube used for television re-ception has two identical plates mountedparallel to each other and separatedabout 1/16 inch. The tube is filledwith neon gas.


AVERAGE CHARACTER -

DETECTORS, AMPLIFIERS6.3 Volt Group for

These Tubes Arc Employed Chiefly in AC - DC or

Type Use Base

Bulb(See

illustra-tion)

12 :TING

PlateVolts

CathodeType Fila-

:tientAmps.

Plate(Max.)Volts

Screen(Max.)Volts

6A4/LA Power Amp. 5-3 ST -14 Filament 0.30 1S0 1S0 135165180

6A7 Det. One. 7-2 ST -12C Heater 0.30 loo 2506B7 RF or IF 7-3 ST -12C Heater 0.30 275 125 100

Amp. 180250

6B7 AF -Amp. 7-3 ST -12C Heater 0.30 275 125 250::6C6 RF 6-1 ST -12C Heater 0.30 275 100 2506C6 Det. 6-1 ST -12C Heater 0.30 275 100 250*6C6 AF 6-1 ST -12C Heater 0.30 275 90 250*6D6 RF 6-1 ST -12C Heater 0.30 275 100 2506D6 AF 6-1 ST -12C Heater 0.30 275 90 250*

36 RF 5-2 ST -12C Heatcr 0.30 275 90 90135180250

36 Det. 5-2 ST -12C Heater 0.30 275 90 25037 Det. Amp. 5-1 ST -12 Heater 0.30 180 ... 90

135180,

38 Power Amp. 5-2 ST -12C Heater 0.30 ISO 180 13539 RF 5-2 ST -12C Heater 0.30 275 90 90

135ISO250

39 AF 5-2 ST -12C Heater 0.30 275 90 250*

41 Power Amp. 6-3 ST -12 Heater 0.40 200 20(1 125167.5180'42 Power Amp. 6-3 ST -14 Heater 0.65 275 275 250

44 RF 5-2 ST -12C Heater 0.30 275 90 90180250

44 AF 5-2 ST -12C Heater 0.30 275 90 250*75 Det. 6-4 ST -12C Heater 0.30 275 25077 RF 6-1 ST -12C Heater 0.30 275 104 25077 Det. 6-1 ST -12C Ileater 0.30 275 100 250*78 RF 6-1 ST -12C Heater 0.30 275 125 1K0

25025))

79 Power Amp. 6-5 ST -12C Heater 0 60 180180S0

8589

Det.Power Amp.

6-46-1

ST -12CST -12C

HeaterHeater

0.300.4))

2751S0 IM)

250190163I,o)po)

Applied through :!:-.0.0ou ohms. "Triode connection. :Pentode connection. 1Plate to plate..Apidied ohms. }For two tubes with 40 volts RMS notated to each crld.


ISTICS OF RADIO TUBESAND RECTIFIERSAC or DC Operation

DC Receivers, Auto Sets, Amplifiers, or in Special Model Receivers

NegativeGridVolts

ScreenVolta

PlateCurrent

ma.

PlateResistance

Ohms

MutualCon-

ductanceMicromhos

Ampli-StationFactor

Ohmsfor

StatedPowerOutput

Undis-tortedpowerOutputmilli_watts

9.0 135 14.0 52,600 1,900 100 9,500 70011.0 165 20.0 48,000 2,100 100 8,000 1,20012.0 180 22.0 45,000 2,200 100 8,000 1,4003.03.0

100100

4.05.8

300,000300,000 947595A 285

.

: : : : : : :3.0 75 3.4 1 Meg. 840 840 .... .. .

3.0 100 6.0 800,000 1,000 800 .... ....4.5 50 0.65 .... .... .. .

3.0 10i) 2.0 1,500,000+ 1,225 1,500+ ... ....6.0 100 Plate curre nt to be adj usted to 0. 1 ma. wi th no Inp ut Signal1.0 50 0.5, 3 Meg. 600 1,800 .... ....3.0 100 8.2 800,000 1,600 1,280 .... ....3.0 75 0.5 1,500,000 600 900 .... ....1.5 55 1.8 250,000 850 215 .... ....1.5 67.5 3.0 300,000 1,050 315 .... ....3.0 90 3.1 350.000 1,050 370 .... ...3.0 90 3.4 400,000 1,100 440 . .... ....6,0 20 to 45 Plate curre nt to be adj usted to 0. 1 ma. wi th no Inp ut Signal6.0 .... 2.5 11,500 800 9.2 17,500 309.0 .... 4.1 10,000 925 9.2 14,000 80

13.5 .... 4.3 10,000 900 9.2 20,000 17513.5 135 9.0 102,000 975 100 13,500 5253.0 90 5.6 375,000 960 360 ....3.0 90 5.6 540,000 980 530 . ..3.0 90 5.8 750,000 1,000 7503.0 90 5.8 1,000,000 1,050 1,050 .

1.0 67.5 0.5 2 Meg. .... .... ....10.0 125 11.0 100,000 1,525 150 11,000 65012.5 167.5 17.0 85,000 1,800 150 9,500 1,25013.5 180 18.5 81,000 1,850 150 9,000 1,50016.5 250 34.0 100,000 2,200 220 7,000 3,000.3.0 90 5.6 375,000 960 360 .... ....3.0 90 5.8 750,000 1,000 750 .... ....3.0 90 5.8 1 Meg. 1,050 1,050 .... ....1.0 67.5 0.5 2 Meg.2.0 , ... 0.8 91,000 1,100 100 .... ....3.0 100 2.3 1,500,000+ 1,250 1,500 .... ....7.0 100 Plate Curre nt to be adj usted to 0. 1 ma. wi th no Imp ut Signal3.0 75 4.0 1,000,000 1,110 1,100 .... ....3.0 100 7.0 800,000 1,450 1,160 .... ....3.0 125 10.5 600,000 1,650 990 .... ....0.0 .... 7.5 No Sign al Applie d0.0 .... 44.0t Class B Operation .... 7,0001 5,500

20.0 8.0 7,500 1,100 8.3 20,000 35020.0 160 17.0 3,000 1,570 4.7 7,000 30017.0 163t 17.0 79,000 1,575 125 9,000 1,25018.0 180: 20.0 82,500 1;635 135 8,000 1,5000 .... 3.0 Class B Operation .... 9,40011 3,500tt

f50 volts RMS applied to two grids.peonverslon Conductance. (i'ourtexy. Ifyyrade Sylvania Corp.)


2.5 VOLT GROUP FORIn this group are listed tubes that are

more commonly used. They will befound in most of the up-to-date a.c. re-ceivers, with a few possible exceptionswhere the tube is designed for suchspecial work, that it may be only em-ployed iu such equipment or apparatus.

The 59 or 2A3, are examples that may

be placed in this category; although thelatter type is employed in some verylarge and expensive receivers to deliverlarge power outputs to obtain tremen-dous volume levels. The 59, however,is almost always used exclusively inaudio amplifiers for power amplificationpurposes, and either as a single class A

Type Uso Base

Bulb(See

illustra-tion)

CathodeType

RATING

PlateVolts

Fill"-mentAmps.

Plate(Max.)Volts

Screen(Max.)Volts

2A3 Power Amp. 4-1 ST -16 Filament 2.5 275 ... 2503002A5 Power Amp. 6-3 ST -14 Heater 1.75 275 275 2502A6 Det. 6-4 ST -12C Heater 0.80 250 2502A7 Det. Ose. 7-2 ST -12C Heater 0.8 275 jot') 2502B7 RF or IF 7-3 ST -12C Heater 0.8 275 125 100Amp. 180250

2B7 AF -Amp. 7-3 ST -12C Heater 0.8 275 125 250tt24-A RF 5-2 ST -14C Heater 1.75 275 90 18025024-A Dot. 5-2 ST -14C Heater 1.75 275 90 250*24-A AF 5-2 ST -14C Heater 1.75 275 90 250*

27 Amp. 5-1 ST -12 Heater 1.75 275 ... 90135180

27 Det. 5-1 ST -12 Heater 1.75 275.

i55235 RF 5-2 S -14C Heater 1.75 275 90 18025035 AF 5-2 S -14C Heater 1.75 275 90 250*45 Power Amp. 4-1 ST -14 Filament 1.50 275 ... 18025027546 Power Amp. 5-4 S-17 Filament 1.75 400 250 250300400

47 Power Amp. 5-4 S-17 Filament 1.75 275 275 25051 Amplifier 5-2 S -14C Heater 1.75 275 90 180250

55 Det. 6-4 ST -12C Heater 1.00 275 .. 25056 Amp. 5-1 ST -12 Heater- 1.00 275

.....- 25056 Det. 5-1 ST -12 Heater 1.00 275 250

57 RF 6-1 ST -12C Heater 1.00 275 100 250

57 Det. 6-1 ST -12C Heater 1.00 275 100 250*57 AF 6-1 ST -12C Heater 1.00 275 90 250*58 RF 6-1 ST -12C Heater 1.00 275 100 25058 AF 6-1 ST -12C Heater 1.00 275 90 250*59 Power Amp. 7-1 ST -16 Heater 2.00 275 275 250

250400

*Applied through 250,000 ohms. **Triode connection. t PentodettApplied through 200,000 ohms. ftFor two tubes with 40


AC OR DC OPERATIONtube to drive two 59's in push -push orclass B operation, or in either of the aboveas a final stage for large power outputs.

The 2B6 TubeThis tube is not described in the list-

ing below. It is a duplex triode that hasnumerous features that enables it to beemployed as a class B amplifier tube

with the advantages of the high qualityfound in class A systems.

Full data pertaining to this tube willbe found in the September, 1933 issueof Radio Craft magazine. Pertinentdata regarding circuit applications, com-plete characteristic curves, resistorvalues to employ, etc., are all included.

NeeativeGridVolts

ScreenVolts

PlateCurrent

ma.

PlateResistance

Ohms

MutualCon-

ductanoeMicromhos

Ampli-ficationFactor

Ohmsfor

StatedPowerOutput

Undis-tortedPowerOutputmilli_watt,

45.0 60.0 765 5,500 4.2 2,500 3,50062 40 per tub e Push Pull 3,00011 15,00016.5 250 34.0 100,000 2,200 it'..1 7,000 3,0002.0 0.8 91,000 1,100 100 .... ....3.0 100 4.0 300,000 475A3.03.0

10075 38 .8. 4 8831)Meg.

950840

285.840

3.0 100 6.0 800,000 1,000 800 .

4.5 50 0.653.0 90 4.0 400,000 1,000 400 .... ....3.0 90 4.0 600,000 1,050 6305.0 20 to 45 Plate curre nt to be ad justed to 0. 1 ma. wit h no Inp ut Signal1.0 25 0.5 2,000,000 500 1,0006.0 2.7 11,000 820 9.0 14,000 309.0 4 . 5 9,000 1,000 9.0 13,000 80

13.5 5.0 9,000 1,000 9.0 18,700 16521.0 5.2 9,250 975 9.0 34,000 30030.0 Plate Curre nt to be ad justed to 0. 2 ma. wi th no Inp ut Signal3.0 90 6.3 300,000 1,020 305 .... ....3.0 90 6.5 400,000 1,050 420 .... ....1.0 45.0 to 67.5 0.5 2 Meg.

-3:531.5 31.0 1,650 2,125 2,700 82550.0 34.0 1,610 2,175 3.5 3,900 1,60056.0 36.0 1,700 2,050 3.5 4,600 2,00033.0 250 22.0 2,380 2,350 5.6 6,400 1,2500.0 0 4.0 Class B Operation .... 5,200 16,000tt0.0 0 6.0 Class B Operation 5,800 20,000

16.5 250 31.0 60,000 2,500 150 7,000 2,7003.0 90 4.5 300,000 1,020 305 .... ....3.0 90 6.3 400,000 1,050 420 .... ....

20.0 8.0 7,500 1,100 8.3 20,000 35013.5 5.0 9,500 1,450 13.8 . . ....20.0 Plate curre nt to be ad justed to 0. 2 ma. wi th no ut Signal3.0 100 2.0 1,500,000+ 1,225 1,500+ .... ....6.0 100 Plate curre at to be ad justed to 0. 1 ma. wi th no Inp ut Signal1.03.0

50100

0.58.2

3 Meg.800,000

6001,600

1,8001,280

........ ........3.0 75 0.5 1,500,000+ 600 900

28.0 250** 26.0 2,400 2,600 6.0 5,000 1.25018.0 2501 35.0 4,000 2,500 100 6,000 3,0000.0 13.0 Class B Operation .... 6,000' 20,00011'

connection. 11Plate to plate.volts RMS applied to each grid.

t50 volts RMS applied to two grids.AConversion Conductance.


Some of the tubes listed here are em-ployed in the older models of battery ord.c. receivers only. These include thefollowing types that are listed, the 01A,12A, 22, X99, V99, and the 00A. Thetype 26 tube is a heavy -filament tubewhose construction made it adaptable fora.c. operation in sets that were manu-factured several years ago. Many ofthese early a.c. receivers performed ex-

SPECIALccllently and are still in use, althoughthis tube has been replaced by the 27 andscreen -grid types that are much moreefficient. The 485, 182B, and 183 arespecial tubes designed for replacementin Sparton receivers. Complete data onall of the tubes that are employed inSparton receivers is given in a charton pages 38-39.

Type Use Base BulbCathode

Type

FILAMENT RATING

PlateVoltsVolts Amps. Supply

00-A Det. 4-1 S-14 Filament 5.0 0.25 DC 45

01-A Dot. Amp. 4-1 S-14 Filament 5.0 0.25 DC 90135

10 Amp. 4-1 S-17 Filament 7.5 1.25 AC or DC 250350425

12-A Dot. Amp. 4-1 S-14 Filament 5.0 0.25 DC 90135180

18 Power Amp. 6-3 ST -14 Heater 14.0 0.30 AC or DC 25020 Power Amp. 4-1 T-8 Filament 3.3 0.132 DC 90

13522 RF 4-2 S-14 Filament 3.3 0.132 DC , 13,5

13526 Amp. 4-1 ST -14 Filament 1.5 1.05 AC or DC 90

135180

40 Amp. 4-1 S-14 Filament 5.0 0.25 DC 135180

43 Power Amp. 6-3 ST -14 Heater 25.0 0.30 AC or DC 95135

48 Power Amp. 6-3 ST -14 Heater 30.0 0.40 AC or DC 95125

50 Power Amp. 4-1 S-21 Filament 7.5 1.25 AC or DC 300350400450

71-A Power Amp. 4-1 ST -14 Filament 5.0 0.25 AC or DC 90135180

X-99 Det. Amp. 4-1 T-8 Filament 3.3 0.063 DC 90V-99 Det. 4-4 T-8 Filament 3.3 0.063 DC 90

485 Det. Amp. 5-1 S-14 Heater 3.0 1.25 AC 90120

182-B Power Amp. 4-1 S-17 Filament 5.0 1.25 AC 250183 Power Amp. 4-1 S-17 Filament 5.0 1.25 AC 250

250864 Det. Amp. 4-1 T-9 Filament 1.1 0.25 DC 90

135


TUBESPower Tubes

The 210, and 250, are tubes that areemployed essentially for power amplifi-cation purposes, although the former isalso used extensively as an oscillator orgenerator of high frequency currents(transmitters), where small power out-put is required.

The 43 is a power tube that is em-ployed extensively in midget receivers.The data given for this tube will show

numerous interesting features that makeit particularly useful for adaptation inreceivers of the a.c.-d.c. type.

Special Purpose TubeThe 864, because of its small glass en-

velope and other proportionately lowdimensions, is generally employed as apre -amplifier (AF) in "head" amplifierswhere compactness is essential. It maybe, and is, used as an RF amplifier, orfor detection.

NesativeGridVolts

ScreenVolts

PlateCurrent

ma.

PlateResistance

Ohms

MutualCon-

duetanceMicromhos

Ampli-ficationFactor

Ohmsfor

StatedPower

Output

Undis-tottedPowerr,vUtD1.1.,mini_watts

Grid Re- .... 1.5 30,000 666 20.0turn Fil.

4.5 .... 2.5 11,000 725 8.0 11,000 159.0 .... 3.0 10,000 800 8.0 20,000 55

22.0 .... 10.0 6,000 1,330 8.0 13,000 40031.0 .... 16.0 5,150 1,550 8.0 11,000 90039.0 .... 18.0 5,000 1,600 8.0 10,200 1,6004.5 .... 5.0 5,400 1,575 8.5 5,000 309.0 .... 6.2 5,100 1,650 8.5 9,000 115

13.5 .... 7.7 4,700 1,800 8.5 10,650 260

16.5 250 34.0 100,000 2,200 220 7,000 3,00016.5 .... 3.0 8,000 415 3.3 9,600 4522.5 ... 6.5 6,300 525 3.3 6,500 110

1.5 45.0 1.7 725,000 375 270 .... ....1.5 67.5 3.7 325,000 500 160 .... ....7.0 .... 2.9 8,900 935 8.3 ....

10.0 .... 5.5 7,600 1,100 8.3 ....14.5 .... 6.2 7,300 1,150 ....1.5 .... 0.2 150,000 200 30 .... ....3.0 .... 0.2 150,000 200 30 .... ....

15.0 95 20.0 45,000 2,000 90.0 4,500 90020.0 135 34.0 35,000 2,300 80.0 4,000 2,00020.0 95 47.0 10,000 2,800 28.0 2,000 1,60022.5 100 50.0 10,000 2,800 28.0 2,000 2,50054.0 .... 35.0 2,000 1,900 3.8 4,600 1,60063.0 .... 45.0 1,900 2,000 3.8 4,100 2,40070.0 .... 55.0 1,800 2,100 3.8 3,670 3,40084.0 .... 55.0 1,800 2,100 3.8 4,350 4,60016.5 .... 10.0 2,170 1,400 3.0 3,000 12527.0 .... 17.3 1,820 1,650 3.0 3,000 40040.5 .... 20.0 1,750 1,700 3.0 4,800 7904.5 .... 2.5 15,500 425 6.8 15,500 74.5 .... 2.5 15,500 425 6.6 15,500 73.0 .... 5.0 10,800 1,150 12.5 .... ....4.0 .... 6.0 9,300 1,350 12.5 .... ....

35.0 .... 18.0 3,330 1,500 5.0 4,500 1,75058.0 .... 20.0 2,000 2,000 3.0 4,500 2,00085.0 .... 26.0 1,500 2,000 ....4.5 .... 2.9 13,500 8108.29.0 .... 3.5 12,700 645 8.2

C.

2.0

VO

LT G

RO

UP

-F

OR

BA

TT

ER

Y O

PE

RA

TIO

N

Bul

bC

atho

deR

AT

ING

RA

TIN

GN

egat

ive

Pla

teP

late

Mut

ual

Am

pli-

Ohm

.fo

rtu

ned

Pow

erT

ype

Use

Bas

e(S

eeill

ustr

a-Li

on)

Typ

eF

ile-

men

tA

mps

.

Pla

te(M

ax.)

Vol

ts

Scr

een

(Max

.)V

olts

Pla

teV

olts

()rid

Scr

een

Vol

taC

urre

ntm

a.R

esis

tanc

eO

hms

Con

-du

ctan

ceM

icro

mho

e

&ta

lon

Fac

tor

Sta

ted

Pow

erO

utpu

tO

utpu

tM

uhl..

wat

ts

15 19 30 31 32 32 32 33

34 34 49

Det

. Ose

.P

ower

Am

p.D

et. A

mp.

Pow

er A

mp.

RF

.AF

Det

.

Pow

er A

mp.

RF

AF

Pow

er A

mp.

5-2

6-6

4-1

4-1

4-2

4-2

4-2

5-3

4-2

4-2

5-3

S -

12C

ST

-12

ST

-12

S-1

2

S -

14C

S -

14C

S -

14C

5-14

S -

14C

S -

14C

ST -

14

Hea

ter

Fila

men

tF

ilam

ent

Fila

men

t

Fila

men

t

Fila

men

tF

ilam

ent

Fila

men

tF

ilam

ent

Fila

men

tF

ilam

ent

0.22

0.28

0.06

0.13

0.06

0.06

'0.0

6

0.26

0.06

0.06

0.12

135

135

180

180

180

135

180

140

180

67.5

....

67.5

67.5

67.5

135

67.5

67.5

...

135

135 90 135

180

135

180

135

180

180*

180

135 67

.513

5li0 IS

O18

0

1.5

0.0

4.5

9.0

13.5

22.5

30.0

3.0

3.0

3.0

6.0

App

rox.

13.5

3.0

3.0

3.0

1.0

0.0

67.5

....

....

....

....

oi:S

67.5

67.5

67.5

135.

067

.567

.567

.522

.5 to

45.

0...

.

1.85

27.0

t2.

53.

03.

18.

012

.3 1.7

1.7 ....

Pla

ts c

urre

14.5

2.7

2.8

2.8

. .. 4.

0

800,

000

Cla

ss B

11,0

0010

,300

10.3

004,

100

3,60

095

0,00

01,

200.

000

1.20

0.00

0nt

to b

e ad

50.0

0040

0.00

0so

o.on

o1.

000.

000

....

Cla

ss B

625

Ope

ratio

n85

090

090

092

51,

050

640

650

650

just

ed to

0.

1,45

056

060

062

0...

.O

pera

tion

500

-..

.

9.3

9.3

3.8

3.8

610

780

780

2 m

a. w

i

70.0

224

360

620

....

2 T

ubes

10,0

001

7,00

05,

700

....

....

th n

o In

p

7,00

0...

....

....

....

.12

,000

1!

2,10

0

185

375

....

....

ut S

igna

l

700

....

....

....

....

3,50

0

*App

lied

thro

ugh

250,

000

ohm

s..f.

Pla

te to

Pla

te.

t50

volts

RM

S a

pplie

d to

two

grid

s.

RE

CT

IFIE

RS

IND

ICA

TE

D P

LAT

E V

OLT

AG

E D

ES

IGN

AT

ES

RM

S V

OLT

S P

ER

PLA

TE

1-V

5Z3

I2Z

325

Z5

80 81 82 83 8486

6

Hal

f Wav

eF

ull W

ave

Hal

f Wav

eV

olta

geD

oubl

erF

ull W

ave

Hal

f Wav

eF

ull W

ave

Ful

l Wav

eF

ull W

ave

Hal

f Wav

e

4-7

4-5

4-7

6-7

4-5

4-6

4-5

4-5

5-5

4-3

ST

-12

ST

-16

ST

-12

ST

-12

ST

-14

S-1

9S

-14

ST

-I6

ST

-I2

S-I

SC

Hea

ter

Fila

men

tH

eate

rH

eate

r

Fila

men

t

Fila

men

tF

ilam

ent

Fila

men

tH

eate

rF

ilam

ent

6.3

5.0

12.6

25.0

5.0

7.5

2.5

5.0

6.3

2.5

0.3

3.0

0.3

0.3

2.0

1.25

3.0

3.0

0.5

5.0

AC

or

DC

AC

AC

or

DC

AC

or

DC

AC

AC

AC

AC

AC

or

DC

AC

250

500

230

125

350

400

550

500

500

225

7500

....

....

....

....

....

....

... .....

....

...

....

....

....

....

....

....

....

....

....

....

50 250 so 100

125

110

135 85 125

250

5060

0

With

cho

k

.

e In

put o

n...

.ly

...

....

.

..

....

....

....

....

....

....

....

....

....

....

....

....

....

....

....

....

....

....


Interchangeable Tube ChartThe purpose of this Chart le to furnish Information se to which typ.a of SYLVANIA SET TESTED V. RES will satisfactorily

replace tube t. pr. of other manufmturers hewing eirnllar. or different, type dmignatiom.As a rule. the lest two digit of a type number are the designeting numerate. In inteechangIng tubes, this rule may be followed

except on special typrs and on tubes recently announced. bearing the new RNA eystets of type numbers. Except on Special Typo.ell Sylvania tubes heretofore designated by emnbol and three numerals have been changed to conform to later dm lane clone. Forexample. SA -NIA is now 411, Sli.227 le now 37, et cetera. Many ol the Sylvania tubes recently introduced beer tsp. numbers...linedunder the new RNA system. or bkh I. cis Mod by letter appearing between two digits azample: 5E31. The dratdigit Ind if tlng the filament voltage clam. the letter being "signed arbitrarily. and the second &sit Indicating the number of usefulelement. in the tube.

Type No. Description Replace withSylvania Type '

Type No. Description Replace 'vitt,Sylvania Type

'110-111A Special Detector 1141A 8051 Full -wave Rectifier 83111-MIA-MIAA. Detector -Amplifier 01A '8I -MM Half -wave Rectifier 81I-KR1 Mercury Rectifier 1-V 82 Full -wave Rectifier 822 Ballast MV Full -wave Rectifier 83 or 513G-2' Special Detector 83 Full -ware Rectifier 833 Ballast 84 Full -wave Rectifier 844 Ballast G84 Half -wave Rectifier(2.4 Special Detector 85 Detector-AVC 855 Ballast.. 88 Full -wave Rectifier 831KM-- ..... Power Amplifier . - 4A4 VI . Power.Amplifier 896 Ballast N Special Detector7 Ballast 91 Ill Volt Converters Ballast 92 Special Detector9 Ballast 95.. Power Amplifier 2A5'II Power Amplifier 10 96 Half -wave RectifierWD -11 Detector -Amplifier 98 Full -wave Rectifier 84'12-'12AM D-12

Power AmplifierDetector -Amplifier

11% 1199 Detector -Amplifier - g:'V99 Detector -Amplifier.'13 Full -ware Rectifier N 1A4 Detector Oscillator 1A614 Detector -Amplifier 2A3 Power Amplifier 2A315 Detector -Oscillator IS 2A3I1 Power Amplifier.... 2A3'16-'1611 half -wave Rectifier III 2A5 Power Amplifier 2A517 Detector -Amplifier 2A4 Detector -AI(: 2A618 Power Amplifier Is 2A7 Detector -Oscillator 2A719 Class Ii Amplifier 19 2116 Power Amplifier'N.. Power Amplifier 20 2B7 Detector -Amplifier 2117KRA Special Detector 523 Full -wave Rectifier 573'22 Amplifier 22 6A4 Power Amplifier 4A4K R21 Special Detector 6A7 Detector -Oscillator 6A7'24-'24A Detector -Amplifier 24A 687 Detector -Amplifier 687KR25 Power Amplifier 2A5 6C6 Detector -Amplifier 6C4255 Detector-AVC 4C7 Detector'26 Amplifier 36 6D6 Amplifier 4D6

Detector -Amplifier 27 6127 RE Amplifier'271151 High Mu Amplifier 54 6E7 RE Pentode.28 General Purpose 61'7 Detector -Oscillator 4F729 Special Detector 29 6Y5 Full -wave Rectifier'30 Detector -Amplifier 30 67.3 Ilaff-wave Rectifier 1-V'31 Power Amplifier 31 414 Full -worse Rectifier 14''32 Amplifier 32 67.5 Full -wave Rectifier'33 Power Amplifier 33 12A5 Power Amplifier I2A5'34 Amplifier 34 12.17..... Rectifier-Amplifier.'35 Amplifier 35 or Si 11Z3 ilalf-w ave Rectifier 1273'36-'36A Detector -Amplifier 34 1423 Half -wave Rectifier 1223'37-'37A Detector-AmplIfier 37 257.3 lialf-wave Rectifier'38-'38A. Power Amplifier 38 2525 9 oltage Doubler 257.5'39-'39A Amplifier 39 oe 44 1828 Power Amplifier (Sparton)... 1828'40 Voltage Amplifier 41 183 Power Amplifier (Sparton)... 18341 Power Amplifier 41 211 Power Amplifier 21142 Power Amplifier 42 257 Amplifier43 Power Amplifier 4.1 291 Triple Twin Tube44 Detector -Amplifier 44 or 39 293 Triple Twin Tube'45 Power Amplifier 45 295 Triple Twin Tube46 Power Amplifier 46 411 Amplifier ,Sparton)'47 Power Amplifier 47 402 Amplifier tSparton)48 Power Amplifier 48 482A Power Amplifier (Spartan)... 7IA49 Power Amplifier 49 4$1213 Power Amplifier (Sparton)... 15211'SO ..... Power Amplifier ye 483 Power Amplifier (Sparton)... 183'SI Amplifier SI or 35 4114 Detector -Amplifier (Sparton). 48552 Class B Amplifier 483 Detector -Amplifier (Sparton) 48553 Class B Amplifier 53 406 Detector -Amplifier (Spartan). 55 Detector-AVC 55 MO Power Amplifier tSparton)... 5056 Detector -Amplifier 56 586 Power Amplifier (Sparton)... 5057 Detector -Amplifier 57 P -86I Full -wave Rectifier 8457A -S Detector -Amplifier 6C6 864 Detector -Amplifier 2640T 86458 Amplifier 58 866 half -ware Rectifier 86658A -S Amplifier 61)6 874 Voltage Regulator59 Power Amplifier 59 876 Ballast Tube59B Power Amplifier 886 Ballast Tube64-64A Detector -Amplifier 36: 985 Auto Rectifier65-65A Amplifier Mt 986 Full -wave Rectifier 83167-67A Detector -Amplifier 37: AD Half -ware Rectifier 1-V6848A Power Amplifier 38: AF Full -wave Rectifier 8269 Special Detector 69 AG Full -wave Rectifier 8370 Detector-AVC BA Special Rectifier'71-'71A-'7111 . Power Amplifier 71A Bil Special Rectifier75 Detector-AVC 75 BR Special Rectifier76.... Detector-Ampllfier 76 GA Power Amplifier77 Detector -Amplifier 77 LA Power Amplifier eA478 Amplifier 78 P7 Power Amplifier 4779 Class B Amplifier 79 PZH Power Amplifier 2A5'80 Full -wave Rectifier 00 Wunderlich . Special Detector

unai.oes new mt downy ionowteosson w, ttottd Tub *IOW* *ben tn... Mom Itartater et At. N11.49111Pal AAA,. my.. *Mew.,

N4.11 -.ht. won. tt.44.44...4.4tAie.,-hold tai..- tA twt.l.t. 14 of.c.F 1.44 tA

MODERN 1*.lcITM TUBEN

SPARTON TUBEThese data are supplied with the in-

tention of supplying a dearth of char-acteristics or specifications of tubes thatare employed in Sparton receivers. Itis conceded by Service Men that replace-ment tubes for these sets are generallydifficult to obtain; or else, because ofthe special nature of these tubes, they

are priced considerably higher thanstandard types. A careful study of thosetubes will show that the differences areslight, and that with a few minorchanges in the receiver's circuit -stand-ard type tubes that are readily available-can be readily adapted. Not all ofthe tubes listed are different from stand -

miassisesGENERAL DETIICTION

Hue

Side Pin. 4 -Prong

Use HeaterFilament

S.PPI7

4144°444.°`4.44Dimosions FdansentTerminalVoltage

Films. ,CurrentAmperes

DetectorPiste

Voltage

GridReturnLead to

Detectorput. cagg,g, maAmis.,.Height Diens

141 Poster Amplifier A.C. or D.C. 614. Ifs' 1.1 1.55 . ....... _ . ... ... _...

401 Side Pia. RProeS Detector Of Amplifier A.C. of D.C. I' 11/4 8.11 1.511 45 cafit. 5

Li461.A Standard.RProns mass, or Amodier D.C. 411' 1 6 II .1111 N +1

410 Stsodotd.4-Prons Power Amplifier A.C. or D.C. 641i' 56. ?A

1.4- -..........

IA

-- --.... .....

--- .11--

1.6

1111A Itandard.4.Prong Detector 0, ergpagr D.C. 411, 151" LI .54 RI +I41RA Standsrd.4-Pron8 Power Amplifier A.C. or D.C. Sir 111' 5.4 J6 --....-

4" livinclard.414..6 R.F. Amp. or DOW.. A.C. or D.C. 134' 111' All 1.75 IS -IN Cstli.

644 Ihendecd.11-Prong Audio !req. Amplifier A.C. or D.C. Of' lir ii44 Iltesdard.4Prong Amplifier A.C. or D.C. 411' 151" i.e

417 Scathed. &Prong Detector or Amplifier A.C. or D.C. CV 111' SA 1.711 1141 fali.

4511 Standsr4.4Pros5 Detester or Amplifier D.C. 454' 1A' if AI 45 +1431 Standard.4Pross Poem Amplifier D.C. 4511. ' 111. SA .11

Ma &endive.41,40Ni Regis Ism. Amplifier D.C. ISS 111' All

4" Stssder4.4-0rsitS Remade Power Amplifier D.C. 411' 111' g.. si - .... ..... ...

441 Standard. 5Prosl Detector Amplifier A.C. or D.C. dfli. 111' LI 1.14. PI Calk. 1.0_,.,

6.6 5tendard.11.Prong Dam Frog. Amplifier D.C. 611' 1A'6.111 --. --........

411f stadard31-Prong Detector or Amplifier D.C. 1154. IA' CS CI Cads .11-10

W Stailderd.11ProsS Pentode Power Amplifier D.C. 1111. IA' AR _____ -.... .....

-.........4411 Stendard.43ree5 Power Amplifier A.C. or D.C. 616. SA' CI 1.6 .....-----HT Stadard,11-00,04 Pentode Power Amplifier A.C. or D.C. $34' flh AS 1.1

4" tuueara.-Proes Power Amplifier A.C. or D.C. 0511 1111 7.6 1.38 ...... - . .... .._...

444 1tsaderd.40Pron6 Pall Wm Rgatigs. A.C. OS" eh' 4.11 LI

661 Itandard.40rosii Da we,. p.a.. A.C. 1134" IA' 7.4 LIS

41141 Standstd.RProng p.a. Amass., D.C. 6)4' 514' 1.1 AI -. .... .. ..... -YRS Standard.14Prool Rower Amplifier A.C. or D.C. M. 5l4 ISO 1.N

444 Sunidard.414.4.6 Power Amplifier A.C. or D.C. 134' 11/4" SA 1.11

464A Standord.4Pcong mtge., or Argplifis, D.C. 411' Ill' 14 1.4 114 Catb. 6.5

4115 gitendortt3141446 rOOKtOf or Amplifier A.C. or D.C. 411' 111 SA 1.1 134 Cad.. 11.111

400 illelidael.Riliuns Radio Pros. Amplifier D C. 411' 111. 4.0

Ikeemass Ord .st.e. I o use in Aucemoblie ReceiversTRessasessidod value fm us* In Receivers designed for 110 woks D.C. operodse.

MODI:c\ F.IrITMBEs 39

CHARACTERISTICSard types, although the first or prefixnumber for the entire listing begins withthe figure "4," whereas standard makesof tubes employ no such prefix number-ing system. Where both the types areidentical in specifications and require-ments, it may be generally recognizedby the similarity in the assigned type

ii.imbers designating the respectivetubes.

Sparton tubes that are immediatelyreplaceable, without any circuit changesnecessary, with those of other manu-facturer's are listed separately in aspecial chart that precedes this, andwhich data was compiled by the Hy -grade Sylvania Tube Corp.

AmplifierPlate

Voltage

BiasVoltage -

IN

D. FriO.

A.C.O. Fd.

60.0

S.101 11.6

Is 1.51110 1111

UINO400

11507.0810

N185

toO .0

166167.6160

0.0 11.11ILO16.0

IM1.6L S

LS6.11

101

15.0IN

1.0

Li0.0

1.11.5

1.0

5.5

ISA

leN

5.516.5

N toIN

8.0

156

505 LIO Al

136US.

Lit1.50Li

155 It

151

III

18.6

60.0

15.5

tN 41.08411 SOS105 NSIII 84.0

46.0411.070.0NS

AMPLIFICATION

And fierPlate Screen

Current Grid7olte

Amperes

Screen Current PlateMilliamperto

tn.,..d.m.Oknis

0,050 I

0.0007.000

158.0

11.00010.000

10 0.0001111

IS6,1546.000

0.0 6.0005.000

5.5 5.000517.0

4.7005.550

4.11 75 Not Over One -Third d 400.005CID Plate Curran 40.000

0.6 MORN

LS4.8

LRON

ON

. 7.4 7.111

0.07

ISSNLIN

LI ELM

11.0 4.140

1.5 47.5 Ilea Over One-Tbird of 101100Plate Ceded

14.0 IN 411.1140

7.0 N 5.6 100.111Man mina

1.5 667 Not Over OutsT1drd of 200.00011.45.5

47.6*71

Plata Coder MOOSSMARM

2.7 11.600Ci 10.000

105 L5 110.000

1.0001.754

264 0.5 NANAINLON

lime

M'"4 Voltage 1 lotConduct. sa.pid. Maximum

nce Cu,. p.,,,,s, UndidortedMit rondos

; Ontsom

Usiiitotud0411141

111101,4616

1060 I 8.0

1000 LO1100 4.7

711 4.0500 0.0

11.601NAN

ION LO1660 101610 ILO

IS.N11111.16010.111116

1040 161100 16

LONLIMO

N110

INS 6.51710 ILIIMO

11.101.

108711. Ufa

10011 4041000 4011

NS IMO

1/211INN

4.011711 LS

N

O N1L15.511

7N174 0.0

11110 404

TANI

IAN Commed

11110 1711060 ON1140 Rd

754 LS844 0.8

14SOWIN 70

050 160

1514/ 15SON LiSUM IN

16.0 Ws

LON TN1111

7006

IONNOS

1.005 01001.600 NN

LS 1000 100Li CLOS 14/411

4.1LS =

Midianite A.C. Voltage Per Plate IN Vold 11..M.LMaximum Rectified Current 126 M.A.

Maximus A.C. Voltage Per Plato 760 Vold RMS.Maximum Rectified Current MI Y.A.

NO

854

IsIN

46

I 11.6 ss IS

46.6016

U.S66.5

NN

MI MI

LON INS

....__

0.0

ION ILO

LOIN ION $.0IAN SON LS

10.110 1I60 1LS*US ISM ILI

15.586 11115 10.0g.df ISM ILI

4000

41411

1400

8111105 466 11.4

rourtorP, (parka Withington Co.

WESTERN ELECTRIC

Type Purpose

RATINGScreenVoltsBase FILAMENT Ott HEATER Plate

VoltsVolts Amps. Supply

101-D Detector or Amplifier 4 prong 4.5 1.0 D. C. 190 -101-F Detector or Amplifier 4 prong 4.1 .5 D. C. 190 -205-I) R. F., A. F., Det. or Use 4 prong 4.5 1.6 D. C. 370 to 400 -215-A R. F., A. F., Amplifier 4 prong

(peanut tube)1. .25 I). C. 100 -

231-D A. F., Amplifier 4 prong 2.9 to 3.4 .06 I). C. 135 -242-A Use., R. F. or A. F. Amp 4 prong 10. 3.25 A. C.

D. C.1250 -

244-A A. F. Amplifier 5 prong

5 prong

2.

9...

1.6 A. C.D.

180 -247-A A F. Amplifier 1.6 A. C.

1). C.180 -

249-A Half -Wave Rectifier 4 prong 2.5 7. A. C. 6500 A. C. -252-A Osc. or A. F. Amplifier 4 prong 5. 2. A. C.

D. C.

A. ( '.D. C.

450 -254-A R. F. Amplifier or ()sc 4 prong 7.5 3.25 750 175

254-B R. F. Amplifier or ()sc . 4 prong 7.5 3.25 A. C.1). ('.

750 150

256-A Special 5 prong 2.3 1.7 A. C. Special Rectifie

259-A R. F. or A. F. Amplifier 5 prong 2. 1.6 A. C.1). C.

180 90

262-A A. F. Amplifier 4 prong 10. .32 A. ('.1). C.

I). C.

180

100

--264-A A. F. Amplifier 4 prong 1.5 .3

271 A A. F. Amplifier 5 prong 5. 2.0 A. C.D. C.

400 -272-A A. F. Amplifier 5 prong 10. .32 A. C.

D.180 -

274-A Full -Wave Rectifier 4 prong 5. 2.0 A. C. Approx.525 RMS

-275-A A. F. Amplifier 4 prong 5. 1.2 A. C.

I). C.250 -

276-A R. F. -A. F. Amplifier, Ose. 4 prong 10. 3. A. C. 1250 -277-A Special 4 prong 5. 9. A. C. - Relay

280-A Half -Wave Rectifier 4 prong 2.5 3. A. C. 3500 -282-A R. F. Amplifier, Osc 4 prong 10. 3. A. C.

1). C.1000 250

284-A Amplifier, Ose., Mod. 4 prong 1 10. 3.25 A. C. 1250 -40

TUBES

PlateCurrentM. A.

Ampli-Factor

fier

PlateResist.

LoadResit

IN'I 1 It -ELECTRODE CAPACITIESIN rrliour SOCKET, in mmf. Power

OutputOutputGrid

Voltage(Class A)

Power(e)litimil

Push -PullP. to C P. to F. C. to F.

8.35 5.95 5,600 11,200 5. 2. 3.7 230 -18 -7.5 6.5 5,400 11,200 5.9 3.7 5.2 240 -16 -

21. 7.3 4,450 8,900 4.8 3.3 5.2 1,200 -30 12 watts

1.9 5.6 14,800 - 2.6 1.2 1.6 - -10 -2 . 5 7 . 8 14,600 29,200 3.2 2.5 2.4 - -7.5 -

85.0 12.5 3,500 7,000 13. 4. 6.5 10,000 -50 125 watts

6.0 9 . 7 - - 3.3 3.7 3.8 - -10 -3 . 8 14.6 16,000 - 3.2 2.7 3.4 - -7 -

1100. - - - - - - - - -43. 5.0 1,700 - - - - - -65 -60. 80. 80,000 - .1 9.4 4.6 - - -75. 100. 75,000 - . 085 5.4 11.2 - - -

of Low In ternal I mpedanc e for Rel ay or Trig ger Action Circuits

7 . 5 480. - - .004 5.8 14.0 - -1.5 -2.8 14.9 17,500 - 1.9 4.0 1.8 - -7.5 -2.6 7. 11,800 - 5.3 2.2 3.5 - -7. -

39.0 8 . 5 2,850 - 5.3 3.8 6.5 - -30 -5 . 9 5 . 5 7,200 - 2.8 2.6 3.4 - -21 -

Approx.125.

- - - - - - - - -52. 2.85 1,000 - 12. 3.2_ 6.8 - -60 -

850. 12. 3,500 7,000 9. 4. 6. 10,000 -50 -Tube - - - - - - - - -500. - - - - - - - -100. 100. 70,000 - .2 6.8 12.2 - - -100. 4 . 7 1,600 3,200 8.2 7.8 7.0 16,600 -106 -

41

31012Ela VACUUM TUBE.

BASES AND BULBS

6-4

BOTTOM VIEW OF BASES

6-5

5-I 5-2

G2 63

0 06-6 6-7

SYMBOLSF-Filament; H- Heater; P-Plate;K-Cathode; G-Grid; GI-Inner Grid;G2-Screen Grid; G3-Suppressor Grid;Go-Anode Grid; Dl D2-Diode Plate;NC-No Connection 1-Adjoining Elements

062

0 0r. f-63

5-3

42 GI

PO 06

7-3

MODERN 7TBE.N. 43

TUBE SYMBOLSWhereas it was simple for the early reader of radio periodicals to locate the

various tube connections of the early three -element tubes, and to understand schem-atic diagrams indicating tubes of this type, the problem is not so simple with existingtubes that incorporate 6, 7, or more elements. To facilitate matters for the ServiceMan, who must trace wiring diagrams, and others who may desire to know elementsemployed, representative symbol, and the position of its respective base pin to whichit is connected, this chart will prove most helpful.

4A 4B 4C 4D 4E 4F 4G 4HP P

Sc0PC

F F

P P

P P

F6 6F

P P P P

4-AIR-

II,St

9,F+ . - 411 -

F F

FF

NCP

F

F

- .

AD+

K

H H

filk3A 58 3C 5D SE 5F 7A 7B

P P P p P

Ala

GO KP SH, F F

H W H

KH

P KP H F1

KH

;G KP H H

KH ,X H

(G)KP H H

K

Gs GiK K

H H

8A 6B 6C 6D 6E 6F 6G 7CP P

'.. G

P

SiP P P

K

P P

G2

D

H

c. 4, Fl

SrSc

R

G

F eh6 *ILI,,,ll H

H

SY Pl G; K

H

K

G *G K HH

411&

Sce *G 414Fahb0D

KH

Di .o H

G

G a7

G

% P

F F

G

G

P G re PHO-HO

P

BOTTOM VIEWS OF BASES AND SCHEMATICS OF TUBESS1111101A- P- Filament. II- Heater. P Plate. IC C.atbode. Grid. G Ismer Grid. G2.Serioad Grid. GS Third GM. j A.110.9

G4 -Fourth Grid. SC -Saes GM. Dl D2 Diode Plate. NC No Connecta= SP Siiippromor Grid. 1 '"

nor a RRANGEMENTS BY MI5 TYPICS?jilt lInae :1'2.. R....np_. Bane 1;_m. BrMft Baas00.4 4.4 1a IC 30 SC 69 68 1128 4.401.A

24.5IC

1920

654A

4142

OC11C

714175

4.4ID

DM465

4AliA

34

1177

IC2426

SII44

4344

6CSC

7778

SA1IA

4462A3

IF4A

56

ICIC

2730

11A4.4

4548

4A5?

7980

IF4D

2A52A7

6078

78

IC40

II32

4A4B

4748

51176C

8182

454D

38751.3

704D

910

404A

8884

5D411

SO55

4.8IlD

8384

4D55

11A7687

787C

ISA14

AA58

3436

AB55

5657

5A6A

8589

6D11)1

112126E6

MRSO

111/

5116/1

27 54140

5899

GAIA

298VIM

4A40

TUBE TYTIS BY BATE ARRANGEMENTSBasaIA TSP. Baas Sipa Ram Type Baas TIP

00-A. ID 80, 83, SD 23. 47 7A 5001-A. 92.

52.8 1?.8446

711 2A7.6A7

121.0110,911.110,

4547

81*MD

4A 17, IS.77.76.

7C 187.4117

31. 43..50. 7IA,

404111

TOO15E2 68

89IS

X411tali, .58. 17.17.37. 54,

GC 16.41.It 48.

182.2A3, SS

684.II. II. 111D

46 IIISi. 7S,

404C

32. 94.8. 3. 4.

U. SA24 4Z

II19

4. 6 7.A b.

IC 6944 7 8?so

7415E4

Courtesy Phileo Radio & Tekv. Corp.

44 .1101)1:1:N VACUUM 'IT I:I

TUBE APPLICATIONS AND CIRCUITS

Various circuits are shown here to illustrate the applications of tubes,(courtesy RCA-Radiotron, Inc.) particularly those that are latestand which may be employed for a multiple number of functions.

A TUNED RADIO -FREQUENCY RECEIVER CIRCUITWITH DELAYED A.V.C. AND 1NTERCHANNEL NOISE SUPPRESSION

DIODE -DETECTOR A -F K..PLIFIERR-4- AMPLIFIER P -F AMPLIFIER R -F AMPLIFIER ca DAM. C. AND NSC. TYPE 57TYPE 58 y, TYPE 58 T TYPE 58 TYPE 55 R4

T

15 V.K.C,

(CAMP I

FUSE

12:= 250000 OHMSR2.= 300 OHMSR3= 20000 OHMSR4= LO MEGOHMRs= 300000 OHMS(VOL. CONTROL)R8.= 500000 OHMSR7= 50000 OHMSR8= 410 OHMS (2o0WATT)118= 10000 -20 OHMSL = R -F CHOKE ,60 MILLIHENRIESL 1 = HIGH-OUALIT Y R -F CHOKE ,85 MILLIHENRIESL2= FILTER CHOKE1400 001-1615,30 HENRIES AT 00 MA,L3= SPEAKER FIELD. 1250 OHMS

432

lF-

L, _I, L340 V. i25v.I=100 MA. APPRO.(

C =GANGED TUNING CONDENSERSC1=03 gr.C2=0.00005 µf.c3=0.0091pr,C4= 8-16).4f tLOW VOLTAGE)C5= 003µf.Cs= BO gf: (500 VOLT ELECTROLYTIC)C7 0.05pEC8- 001 }1f.C3= 0.5 pf.T = POWER TRANSFORMERTI AND T2 -SEE NOTET3= OUTPUT TRANSFORMER,PRIMARY IMPEDANCE 7000014.6

NOTE : THE CONSTANTS OF THE R -r TRANSFORMERS T1 AND T2 WILL DEPE,0 UPONTHE FRCOuENCy RANGE AND GENERAL LAYOUT

OF THE SET. THE BLEEDER RED STANCE VALUES WLL VARY WIDELY N INDIVIDUALSETS:THEY SHOULD BE CHOSEN TO GwETHE VOLTAGES INDICATED ACROSS EACH SECTION.

sPraTYPE

Vs PVER

O"."FCR

SPEAKER

TYPICAL PENTAGRID CONVERTER CIRCUITR -F 1-r

INPUT TYPE 2A7 OR 6A7 OUT PUT

SIGNAL GRID BIAS PLATESUPPLY

C AlfCci4GANGED VARIABLE CONDENSERS2-C3= PADDING CONDENSERC.4=GRiD CONDENSER OF 200µ}1f.LI = 05CiLLATOR GRID INDUCTANCE.COUPLEDL2=OSCILLA1OR PLATE INDUCTANCEM s MUTUAL INDUCTANCE OF LI & L2R:=OSCILLAIOR GRID LEAKq2.SELF BIASING RESISTORR3 s vOL TAGE REDUCING RESISTOR OF 20.000 OHMS

(USED ONLY WHEN PLATE VOLTAGEIS OVER 200 VOLTS)

TYPICAL PENTAGRID CONVERTER CIRCUITR-1 INPUT TYPE I.A6

C4

c C3 R1

1---XIBEL2

C1 i-FTOuTPur

1C2 1I`

7 - 0+ 7: 7"SIGNAL ANODE -GRID r IL SCREEN PLATEGRID BIAS SUPPLY SUPPLY SUPPLY SUPPLY

c = p f.CI \7/GANGED VARIABLE CONDENSERSC3= PADDING CONDENSERC4= GRID CONDENSER OF 200 pur

i = OSCILLATORRPGL ATRID E IN

INDUDUCTANDCECTANCE},COLPLEDL2= OSCILLATO= MUTUAL INDUCTANCE OF Li AND L2

Ri= OSCILLATOR GRID LEAK

MODERN VACUUM TUBES

DUPLEX -DIODE PENTODE CIRCUITSUsing Types 2B7 or 6B7 Tubes

HALF -WAVE DETECTOR,SEPARATEA.V.C.FIXED-BIAS AMPLIFIER AF

HALF -WAVE DETECTORDIODE BIASED D -C AMPLIFIER

APPROXIMATE VALUES150 wolf. for 500-1500 Ice.

(71= (450 mmf. for 175 kc.C.2=0. mf.C5=0.1 mf.C4=0.5 mf. or larger4',.=0.001 tut or smaller.

HALF -WAVE DE TECTOR,ANDA.V.C,FIXED-BIAS AMPLIFIER

HALF -WAVE DETECTOR, SEPARATEA.V.C., FIXED BIAS AMPLIFIER

C6=0.01-0.1 mf.4'7=0.0005-0.001 mf.C5=0.1 mf. or largerIti=0.5-1.0 megohmIt..=1.0-1.5 megobnis113=0.1-0.2 megohm1:4=0.5-1.0 megohmns=to megohmN=30,000-100,000 ohms.lt7=0.1-0.2 megobmsE,,=voltage for sensitivity control

Note: Suppressor connected to cathodewithin bulb.

45


APPLICATIONS OF DUPLEXDIODE TRIODE TUBES, SUCH

AS THE 55, 75, 85 AND2A6 TYPES

pb

HALF -WAVE DETECTORFIXED -BIAS AMPLIFIER AF

ll-C6

R C5

C1R4

ww=41114- _411111171:-

C4

C44.-i F-4

FULL -WAVE DETECTORFIXED -BIAS AMPLIFIER

HALF -WAVE DETECTORFIXED -BIAS H -F AMPLIFIER APPROXIMATE VALUES

15o mini for:.00-t7,ou L..C1= 145o mmf. for 175 kr.Ct=0.1 mf.Ca=0.1 mf.C4=0.5 mf. or largerC6=0.5 mf. or largerC.=0.01-0.1 mf.e,=0.0005-0.001 mf.C6=0.1 mf. or larger1%.=0.0001 mf. or smaller

megohmlt2=1.0-1.5 megohms11:,=0.1 megohmIt4=0.5-1.0 megohmit.=1.0 megohmitb=25000-75000 ohmsEb=voltage for sensitivity control.

MODERN V.4rUUM TUBES 47

P

y PENTAGRID CONVERTER,, TYPE 647

11B

X

f 111 = 50000 OHMS(VOLUME CONTROL)

)15v. Cg R2= 150 OHMS!LC C6 R3= 10000 OHMSOR - ."I R4= 430 OHMSO.C.L 1

in 11.1e Os', R6 = 500000 OHMS=A.. Rg Rs= 17500 OHMS

FUSE C 7- R7= 250000 OHMSR8= 62501445(2 wATT)

1....y 25Z5 43 78 R9 = 20000 OHMS(BLEEDER)R18= ISO OHMS (25 WATT)Ti = 456 PC. I -F TRANSFORMERT2 = OUTPUT TRANSFORmER;PRMARY

LOAD IMPEDANCE 4500 OHMSNOTE: THE MECHANICAL LAYOUT OF THE SET WILL DETERMINE TO A LARGE E

NECESSARY TO KEEP HUM AT A SATISFACTORY LEVEL

FIVE-TUBE SUPERHETERODYNE RECEIVER CIRCUITFOR A -C AND D -C OPERATION

I -F AMPLIFIER DETECTORTYPE 78 TYPE 77

.

R CTIFIERTYPE 25Z5

X

Y RIO 77 6A7

SERIES -HEATER CIRCUIT

POWER AMPLIFIERTYPE 43

C = GANGED TUNING CONDENSERSC1 = 0.002 }If,C2 = 0,1mEC3 = OD004 (.1EC4= 10.0 gE (ELECTROLYTIC)

S- 0.0002S LitC6= 001C7 = 6A }AC (ELECTROLYTIC)Ca = 2.0 MCL = R -F CHOKE, 60 MILLIHENRIESLi = 100 VOLT D -C SPEAKER FIELD, 2000 CHASL2 = FILTER 010KE,MAX.REStSTANCE 200 OHAS;

INDUCTANCE AS LARGE AS PRACTICAL

%TENT THE MINIMUM 5121 OF FILTER CHOKE

Illustrating the application of the 6.3 -volt type tubes, in a typical midget receiver

of the a.c.-d.c. variety. The 43 and 25Z5 are 25 -volt tubes whose filament con-sumption is the same as that of the 6.3 volt types.

TWO STAGE A -F AMPLIFIER CIRCUITOUTPUT TUBE

TYPE 53

B- =PLATE SUPPLY :-.2S0 VOLTSGRID BIAS. -3 VOLTSPLATE CURRENT(PER UNIT)5MILLJAMPERES(APPROx)VOLTAGE AMPUFICATION .28.8 PER UNITOVERALL VOLTAGE AMPLIFICATION =720MAXIMUM A -F INPUT .0.013 VOLTS(RMS)MAXIMUM A -F OUTPUT -57.5 VOLTS(RMS)DISTORTION -NEGLIGIBLE

Application of the 53 tube as a class Adriver. It may be also employed as aclass B power stage. See chart forspecifications.

VOLTAGE -DOUBLER CIRCUIT

110KRMS

INPUT

TYPE2525 ic

D-COUTPUT

Tc 1R = HEATER VOLTAGE REDUCING RESISTORC= FILTER CONDENSER

The 25Z5 may be used as a half -waverectifier, a full -wave rectifier, or todouble the output voltage when a.c. isemployed.

48 .1101)1:1:.V 1".1(1.1'.1f 1.1"111,'S

2.0 AMP.FUSE

115V.60 CYCLE

TYPICAL CLASS B AUDIO-FREQUENCY AMPLIFIEROUTPUT 20 WATTS

TYPE 56

F,

TYPE 59 TYPE 59

TO 163 MA.

C, 0.1 m f.C2 0.25 )Jf.C3= 1.0 f.C4: 6.0 pi . (LOW VOLTAGE)C5= 0.06,}11.C9= 1631f. (ELECTROLYTIC)C7= 151.14 . (ELECTROLYTIC)141 = 250000 OHMS (VOL. CONTROL)R2 = 7000 OHMSR3: 100000 OHMSR.: 25000 OHMSR5= 250000 OHMSR6=1100 OHMS

SPEAKERN21

SPEAKERN22

(726 TO .0e MA

+265 V

II

R1=25000 OHMSR6= 3500 OHMSR9=3200 OHMS (10 WATT)T, : INPUT TRANSFORKTER,PRimARY 101/2 SECONDARY=3:1

PRIMARY INDUCTANCE:12H. AT 26MA.12:OUTPUT TRANSFORMER, 6000 ()HAAS PLATE -TO -PLATE73: POWER TRANSFORMER; SHOULD HAVE GOOD

VOLTAGE REGULATION CHARACTERISTICSL1 :15 HENRIES AT 100 MA ;150 OHMS 0-C

RESISTANCE. OR LESSL2=1500 OHM SPEAKER FIELD. 115 VOLTSL3=2500 OHM SPEAKER FIELD. 125 VOLTS

NO1C 'SPEAKERS C,Ff C.AL DESIGNED FOR NIGH POWER ARE RECOMMENDED. CIRCUIT CONSTANTS SHOULD CLOSELYAPPROX MATT 1,40SE C.,.. EN ABOVE FOR SATISFACTORY RESULTS.

Illustrating the application of the 59 tube in a class A driver stage, and a class B

power stage. A 56 tube feeds the 59 (in class A) whose output in turn drives thetwo 59's in class B. To obtain the specified output from a class B stage, it is

essential that the grids of these tubes in this arrangement. ho properly excited.

Push -push a.f. coupling must be used if quality amplification is desired: since the

harmonic distortion that exists in the output of a class B stage is considerable.

and this method of coupling balances out. a great percentage of this type ofdistortion.


APPLICATION NOTE

ON

THE 37, 56, 57, AND 77 TUBES AS

RESISTANCE -COUPLEDHIGH -VOLTAGE AMPLIFIERS

The 37, 56, 57, and 77 type tubes maybe operated as resistance -coupled ampli-fiers with high plate -supply voltages, ofthe order of 500 volts, to provide highaudio input voltage for the operationof large power output tubes.

In the design of power amplifiers, thetubes, the coupling devices, and theoperating voltages to obtain the highestoutput levels with the least amount ofdistortion must be carefully selected.

For representative tubes operated witha plate supply of 500 volts, a plate loadof 250,000 ohms, and a grid leak of500,000 ohms for the following tube, thevoltages developed across the a.c. loadof 167,000 ohms are:

TABLE I

TubeType

Grid -BiasVolts

ScreenVolts

Peak -OutputVolts

DistortionPer Cent

37 --22.5 172 3.556 -16.0 180 5.957 - 3.5 92 180 5.057 - 3.5 90 200 7.077 - 4.5 100 200 9.5

From the standpoint of distortion, the37 is the most satisfactory. The 37,however, requires 6.5 times as great aninput voltage as the 57 to yield thesame output. From the standpoint ofgain, therefore, the 57 is to be preferredto the 37.

An excellent output tube for provid-ing very large audio output of highquality is the 845. This tube operatedas a self -biased audio amplifier with apeak -input voltage of 150 volts is cap-able of an a.f. output of 21 watts. Anyof the tubes shown in the table (the 37,66, 57, and 77) can be used to providethe necessary grid excitation for the 845.

From the plate characteristics of the57 and 77, one might expect that low

distortion at high output voltages wouldbe obtained from these tubes when theplate supply is 500 volts, plate load is250,000 ohms, and grid resistor is 600,-000 ohms for following tube. However,distortion increases rapidly with outputat high plate -supply voltages and, al-though large outputs can be obtained,they may not be sufficiently free fromdistortion. This relationship is indi-cated in Table I. Distortion, incident-ally, is somewhat critically dependentupon screen voltage.

Operation of any of these tubes inpush-pull will provide greater outputat lower percentages of distortion. Theaccompanying tabulation shows self -biased push-pull operation for pairs ofthe same tubes as in Table I with thesame conditions, i.e., plate supply voltageof 500 volts with plate and a.c. loads of260,000 and 167,000 ohms respectivelyper tube. Screen voltage is given forminimum distortion.

TABLE II

Tube Grid -BiasType Volts

Peak -Screen Output DistortionVolts Volts? Per Cent

- -22.5 275 0.756 -16.5 255 1.157 - 3.5 75 300 1.057 - 3.5 75 350 2.577 - 3.5 70 293 1.5

$The peak -output voltage Is that measnr..dbetween plates.

For the 350 -volt output condition in theabove table, the Input to the 57 tubes issufficient to cause some grid current.

Considering both output voltage anddistortion, the 57 provides the mostsatisfactory performance.

In cases where the grid leak of thepower tube is limited to 100,000 ohms,the maximum output of two 57's in push-pull with plate load of 250,000 ohms is315 volts peak with distortion of 1.8%.Screen voltage of 75 volts is used. Theinput signal is that which will Just startgrid current.

Thus, if it is desired to operate two845's in push-pull with a plate voltageof 1000 volts and grid voltage of 166volts to provide approximately 46 watts


of power, very satisfactory results wouldbe obtained by using a pre -amplifierstage of two 57's in push-pull with aplate -supply voltage of 600 volts and acontrol -grid voltage of 3.5 volts.

Where an amplifier is to be used inconjunction with low voltage inputs,the high gain of the 57 is a distinctadvantage.(Courtesy RCA-Rudiotron, Inc.)


New 2.5 Volt Tubes

2A3-A power output triode designed foruse in Class A service either in single

cr push-pull use where a large outputis desired. The mutual conductance isparticularly high, being 5500 microm-hos. With a plate voltage of 250 voltsand a negative grid bias of 45 volts, 3.5watts output is obtainable from a singletube. A pair of these tubes operatingit Class A push-pull with 300 volts onthe plates and with a negative grid biasof 62 volts is capable of delivering un-distorted output of 15 watts.

2A5-This tube is a 2.5 volt heater typeoutput pentode with the same electri-

cal characteristics as Type 42 of the 6.3volt group. When operating the 2A5with 250 volts on the plate, 16.5 voltsnegative grid bias and supplied with apeak signal equal to the grid bias, 3watts may be obtained.

2A7-The electron -coupled pentagridconverter is a five grid electron -

coupled detector -modulator tube with ahigh conversion gain intended forservice in super -heterodyne circuits.Type 2A7 performs the functions of anoscillator -modulator, and at the sametime is a satisfactory volume controltube, thus eliminating the necessity ofhaving separate tubes perform the samefunctions. This is accomplished byhaving a sharp cut-off grid and a re-mote cut-off grid, respectively, performthe duties of an oscillator grid and asignal grid.

297-A double diode -pentode intendedfor service in circuits as a combined

detector, RF, IF, or AF amplifier andAVC tube. This tube is somewhat simi-lar to Type 55 but differs in that itcontains a pentode section instead ofa triode section, thus making possibleadditional circuits applications. Thistube employs the new small seven -pinbase providing separate connections foreach of the two diode plates, makingpossible several circuit combinations.

55-A double diode -triode permittingdiode detection followed by a stage of

triode audio amplification to be ob-

tained from a single tube. Variouscircuit combinations are possible withthis tube, due to the fact that a separateconnection is provided for each of thetwo diode plates. This facilitates theuse of the tube in many special circuitsof AVC, delayed AVC and QAVC types.

59_A three grid power output tube in-corporating a seven -pin base which

provides external connections for eachgrid. By using the flexible wiring pos-sibilities of the socket the set manufac-turer can provide suitable operatingconditions so that the tube may be usedfor three purposes. As a Class A triodeit will deliver 1.25 watts, as a Class Apentode 3 watts, and it may also beused as a Class B output tube. In thelatter service a single 59 is used as adriver followed by a pair of these tubes,the combination being capable of sup-plying up to 20 watts.

NEW 2 -VOLT SERIES FOR BATTERY

OPERATION

IS-The only cathode type R. F. pentodeavailable for battery operation espe-

cially designed for use as detector -oscil-lator. Heater current is .220 ampereat 2 volts.

19-A complete Class B tube containingtwo triode elements. Filament rating

is .26 ampere at 2 volts. Power outputup to 2.1 watts may be obtained with aplate voltage of 135 volts. Designed fora small grid bias to accommodate arange of plate voltages and to securemaximum efficiency by reduction of in-put grid power. Suitable for use withType 30 as a driver.

49-A double grid amplifier tube whichmay be used as a triode, for Class A

service as a driver, or Class B serviceas an output tube, depending upon thecircuit connections. A typical Class Boutput stage utilizes three of thesetubes, or a single 49 as a driver may beused to supply the input power requiredby a Type 19 tube.


New 6.3 Volt Tubes6M-The electron -coupled pentagrid con-

verter is a five grid electron -coupled detec-tor -modulator tube with a high conversiongain intended for service in super -heterodynecircuits. Type 6A7 performs the functionsof an oscillator -modulator, and at the sametime is a satisfactory volume control tube,thus eliminating the necessity of having sep-arate tubes perform the same functions.This is accomplished by having a sharp cut-off grid and a remote cut-off grid, respec-tively, perform the duties of an oscillatorgild and a signal grid.

6132_A double diode -pentode, intended forservice in circuits as a combined detector.

RP, IF or AF amplifier, and AVC tube. Thistube is somewhat similar to Type 75 and85 but differs in that it contains a pentodesection instead of a triode section, thusmaking possible additional circuit applica-tions. This tube employs the new smallseven -pin base providing separate connec-tions for each of the two diode plates, mak-ing possible several circuit combinations.

6C6-kn efficient It. F. pentode of the sharpcut-off type. Recommended for use as de-

tector, or detector -oscillator in superhetero-dyne receivers, as control tube and as audioamplifier with resistance coupling. Short-wave operation has been considered in thedesign of the tube, and inter -electrode ca-pacities kept low for this service. The 6C6is identical in characteristics with Type 57except for heater rating which is 6.3 voltsat 0.3 ampere.

6D6 --A remote cut-off tube otherwise similarto the 6C6 described above. It is designed

for It. F. and I. F. amplification, or for useas a tirst detector in a super. In this latterservice translation gain is lower than thatobtained from Type 006, but AVC voltagemay be applied to this grid to secure increas-ed range of control. Mutual conductance,high plate resistance, and low output capacityare features of the design of this tube. Ex-cept for heater rating this tube is identicalwith Type 58 of the 2.5 volt group.

4I -1n improved cathode type power pen.lode designed especially for automobile

service. Useful in any installation wheremaximum power output is desired with platevoltages not exceeding 200 volts. The tubeis very compact, using the ST -12 bulb and asix -prong base, no top cap being required.The tube will deliver 1500 milliwatts with180 volts applied to plate and screen, andwith 14.0 volts negative bias on the controlgrid.

42-k beater type output pentode of largersize than Type 41, and designed for oper-

ation on voltages up to 250. Compared withType 247, the tube has the advantage ofhigher power output, separate cathode termi-nal and hum -free performance. The separatecathode is particularly advantageous in mak-ing complete self -bias operation possible andeliminating the need for a center tap on the

heater winding. Rugged in mechanical con-sttuction and uniform in characteristics.

755-Is a double diode -high mu triode suit-able for use as a diode detector and a

triode audio amplifier. In addition, auto-matic volume control can be obtained fromthe diode. The triode unit has an amplifi-cation factor of 100. Type 75 is providedwith a 6.3 volt .3 ampere heater, and likeTypes 36, 37 and 38, is manufactured withtriple folded filament giving exceptionallyfast heating time.

77_A triple grid amplifier and detector es-pecially designed to operate satisfactorily

in AC or DC use. Complete internal shield-ing is provided by use of the conventionalouter cage, rigidly supported in the dome topof the ST -12 bulb. Type 77 is recommendedfor biased or grid leak detector service anda low signal input R. F. or A. F. amplifier.

72-A triple grid super control amplifier withre -mote cut-off similar in structural appear-

ance to Type 77. This tube is particularlyadaptable to radio frequency and intermedi-ate frequency stages of receivers employingautomatic volume controlling because of itsability to handle very high signal voltageswithout cross modulation or modulation dis-tortion.

79__A complete Class B tube with two setsof triode elements designed for Class B out-

put service. This tube delivers a power out-put far in excess of that obtainable from anyprevious tube camp:treble with it in size(ST bulb with top cap and six -prong base.)The heater rating is only .6 ampere at 6.3volts. Power output up to 5.5 watts mayhe obtained when the plate voltage availableis 180 volts. Moderate increases in platevoltage result in rapid increase in poweroutput. Each triode element is of doublegrid construction, the two grids being con-nected permanently together. No grid biasis required and distortion is extremely lowdue to careful design.

54_is a heater -cathode rectifier tube whichcan be ii it either in half -wave or full -

wave operation. Because of its compact sizeand efficient operation it is especially adapt-able to automobile B -supply devices. Type84 heater rating is 0.5 ampere at 6.3 volts,and has a maximum load current drain of50 ma.

ge;e_A three grid power output tube incor-porating a six -pin base and a top cap

which provides external connections for eachgrid. By using the flexible wiring possibili-ties of the socket the set manufacturer canprovide suitable operating conditions so thatthe tube may he used for three purposes. Asa Class A triode it will deliver 300 milli -watts, as a Class A pentode- 1500 milliwatts.and it may also be used as a Class B outputtube. In the latter service a pair of thesetubes is capable of supplying up to 3500milliwatts.


Special TubesI-V-A high vacuum half -wave rectifier

of the heater cathode type, with aheater rating of 0.3 ampere at 6.3 volts.This tube is unique in that the voltagedrop is very low, being approximately15 volts. Type 1-V is interchangeablewith the mercury vapor tube, Type 1,and has all the proven advantages ofthe high vacuum rectifier.

5Z3-A 5 -volt coated filament full -wavevacuum rectifier intended for heavy

duty service. The tube is capable ofsupplying approximately twice the cur-rent available from a Type 80 with im-provements in regulation. It should notbe used in place of Type 80 in equip-ment designed for the latter tube.

12Z3-This tube is a half -wave high vac-uum rectifier of the heater -cathode

type, for use in DC power supplyingdevices where there is a load currentnot greater than 60 ma. The heaterrating is 0.3 ampere at 12.6 volts, mak-ing it adaptable for series operationwith 0.3 ampere tubes.

18-A cathode type power amplifier pen-tode with a heater rating of 0.3 am-

pere at 14 volts. The electrical charac-teristics are the same as Type 42 of the6.3 volt group. Type 18 is ideal for 0.3ampere series circuits and is especiallyrecommended for transformerless re-ceivers employing the 25Z5 voltagedoubler rectifier tube.

25Z5-A high vacuum rectifier with a 25 -volt 0.3 ampere heater. This tube is

designed to supply DC power either inhalf -wave or voltage doubling circuitswith a maximum load current of 100ma. It is especially recommended foruniversal service and can be used inseries operation.

43-This tube is a 25 -volt heater typepower pentode designed for use as apower tube for DC line operated receiv-ers, supplying 900 milliwatts with 95volts applied to the plate. Greater out-put may be obtained by operating at re-duced grid bias of 10 volts and over-driving by applying signals up to 14volts. Under these conditions an out-put as high as 1.6 watts is obtainable.Latest construction tubes made in domeshaped bulbs have been especially de-signed for resistance coupled input. Insuch installations the grid bias must bekept at normal value as over -driving ispossible only with transformer coupledcircuits and with suitable transformerdesign. The heater current is .3 ampere,a suitable value for use in series opera-tion with 6.3 -volt tubes.

48-Is a 30 -volt 0.4 ampere heater typepower pentode recommended for DC

line operated receivers. The maximumplate operating voltage is 125 volts.The proper grid voltage is 22.5 with aplate current drain of 50 milliamperes.Under these operating conditions 2.5watts power output is obtainable.

82-A mercury vapor full -wave rectifierwith 2.5 volts, 3 -ampere filament. The

drop in the tube is constant over a widenge of load currents, a characteristic

desirable when supplying receiverswhich include Class B output tubes.Voltage regulation depends only uponresistance of other circuit elements.83-An improved heavy duty full -wave

mercury vapor rectifier with a 5 -volt,3 -ampere filament. This tube is capableof supplying heavy load currents up to250 ma. and is rugged enough to standall normal over -loads. Especially rec-ommended for receivers employing ClassB amplifiers.

Ar,


Additional Tube Types(Courtesy RCA-Radiotron Co., Inc.)

The '00-A is a three -electrode detectortube of the gas -filled type for use instorage -battery -operated receivers. As agrid -leak detector, this tube is especiallyeffective on weak signals. See RADIOTUBE CHART for operating conditions.

The RCA Radiotron types WD -I1 andWX-12 and the Cunningham types C-11and CX-12, are detector -amplifier tubesof the three -electrode construction foruse in older types of dry -cell -operatedreceivers. Their electrical character-istics are identical. The 11, however,fits only the WD socket, while the 12fits the standard four -contact socket.

The '40 is a storage -battery tube ofthe three -electrode high -mu type de-signed for use in resistance- or imped-ance -coupled amplifier or detector cir-cuits.

The RCA Radiotron UX-874, or theCunningham CX-374, is a voltage -regu-lator tube designed to maintain constantd -c load current. In such devices, the874, or 374, maintains an approximatelyconstant d -c voltage of 90 volts acrossits terminals for any current from 10to 50 milliamperes. This tube consistsof two electrodes (a cathode and ananode) in a gas -filled bulb. It requires125 volts for starting and shows a pro-nounced glow in operation. This typehas an S-17 bulb and a medium 4 -pinbase.

The RCA Radiotron UV -876, or theCunningham C-376, is a current regu-lator designed for use in series withthe primary of a power transformer toabsorb the voltage variations normal toa -c power lines. The operating currentof this tube is 1-7 amperes for a voltagerange of 40 to 60 volts drop in the tube.

The RCA Radiotron UV -886, or theCunningham C-386, is similar to theUV -876 and C-376. The operating cur-rent of this tube is 2.05 amperes for avoltage range of 40-60 volts drop in thetube.

The RCA -868 is a sensitive phototubeof the gaseous type. It is particularlywell adapted for use with sound -moving

pictures and for experiments with lightbecause of its excellent response to in-candescent lamp sources of light.

The New Tube.Numbering System

Type numbers for new tubes are nowbeing assigned in accordance with thenew system adopted in the early partof 1933 by the Radio Manufacturers As-sociation. A new system was requiredbecause practically all of the availabletwo and three digit numbers has beenutilized.

The new system, which provides forfuture expansion of tube types, ordin-arily requires only three symbols toidentify a tube. These symbols arearranged with a numeral first, then aletter, and finally, a numeral. An ex-ample of the new type designation isthe 2A5.

New type numbers are formed accord-ing to the following simple rules. Thefirst numeral indicates the filament volt-age in steps of one volt. For instance,1 is used for voltages below 2.1; 2 isused for voltages between 2.1 and 2.9inclusive; 3 for voltages between 3.0and 3.9, inclusive; et cetera. The digit1, rather than the digit 2, is used forthe 2.0 -volt types in order to separatethe 2.0- and 2.5 -volt tubes. Thus, the2.0 volt 1A6, and the 2.5 -volt 2A5.

The letter is used to distinguish thetube type and is assigned, starting withA, in alphabetical sequence. In the caseof rectifiers, however, the assignment ismade, starting with Z, in reverse se-quence.

The final numeral indicates the num-ber of useful elements brought out toterminals. Thus, the 2A5 has five suchelements; a heater, a cathode, two grids,and a plate.

While these rules assist to some extentin classifying tubes by filament voltageand function, the significance of theindividual symbols will in most casesbe inadequate to identify features of atube.


Recent Advances in Tube Design(Courtesy RCA-Radiotron Co., Inc.)

Improvements in radio tube designand construction are not necessarily'united to the forward steps representedby the introduction of new tube types.Existing tube types can be made betterby careful study of their inherent weak-nesses and the adoption of new manu-facturing technique designed to over-come these faults.

The RCA Radiotron Company andE. T. Cunningham, Inc., are constantlyexperimenting to determine how thequality and uniformity of their productcan be improved. The past year hasmarked the introduction of many im-provements in the design and construc-tion of Cunningham Radio Tubes andRCA Radiotrons. Some of these im-provements are readily apparent, whileothers of equal importance are not soobvious.

Dome Bulb Construction

The introduction of the dome -bulbtype of construction has made possiblethe greater uniformity of RCA Radio-trons and Cunningham Radio Tubes.This dome -bulb construction has beenincorporated in most of the newertypes. Older types are being adaptedto this form of construction as rapidlyas development and manufacturing ac-tivities permit.

A mica support at the top of the elec-trode assemble fits into the dome of thebulb, bracing the tube's structureagainst mechanical displacement. Fur-thermore, the greater strength of theelectrode assembly secured by the domesupport has made it possible to simplifythe construction of the tube, thus elim-inating many welds and parts, and re-ducing the chances of error duringassembly.

The resulting increase in uniformityof tube characteristics is a decidedbenefit to the set engineer, since it per-mits him to design receivers with closertolerances and consequently better per-

formance. The greater strength andrigidity of the dome bulb, preventingmechanical injury to the electrodes dur-ing shipment, is assurance that thetubes used by the consumer will meetthe exacting requirements of the setengineer.

Reduced Size of Bulbs

Many new RCA Radiotrons and Cun-ningham Radio Tubes are considerablysmaller than preceding types. In somecases this reduction in size has beenmade possible by the use of better glassand by structural improvements in thetubes themselves. Since more efficientdissipation of heat reduces the limitingeffects of grid emission and stem elec-trolysis, higher outputs are obtainablewith these small sized tubes.

The smaller size bulbs permit a sav-ing in chassis space, a reduction inshipping weight, and the use of lesspacking materials.

Improved Cathode and Heater Designs

New types of cathodes (such as themultifilamentary cathode employed inthe 2A3) have opened new possibilitiesin tube design. Because of the largesurface area of these cathodes, improve-ments in mutual conductance, lowerplate resistance, and greater power arepossible. Consequently, improved re-ceiver performance is possible while thecost of circuit apparatus is lower.

Developments in new and small -sizedcathodes have been incorporated inheater type tubes introduced duringthe past year. The better emission char-acteristics of the new cathodes havepermitted the design of more powerfuloutput tubes, since more plate currentis made available for a given size ofcathode. Because of a decrease in theamount of heat required to produce agiven amount of emission, the newcathodes are economical of heater -powerconsumption.


Smaller size cathodes are desirablebecause they allow the size of the wholeelectrode structure of the tube to be re-duced. Economies in heater powerccnsumption permit savings in circuitwiring and power transformer costs.

A careful study of heater -cathode -de-sign problems has produced a new formof heater which has helped to decreasehum levels. Employing a reversedhelical winding which is baked in a ce-ramic, the new heaters greatly reducethe electro-magnetic field responsiblefor a large part of the hum in heater -cathode tubes. A reduction in heater(cathode) hunt means that the overallhunt may be sufficiently reduced so thatless plate supply filtering will provesatisfactory.

Reduced Grid Emission

Grid emission, which is always atroublesome problem in radio tube de-sign and manufacture, has been greatlyreduced by the application of newmanufacturing methods.

The use of copper side rods, heatradiators, new grid materials, and gridwire which has been carbonized hasaided in the control of grid emission.Certain older types of tubes, such astile 24A, have been redesigned to usecopper side rods for the grid. Copperis a better conductor of heat than ma-terials formerly used for side rods. Thesuperior conduction characteristic ofcopper enables it to carry off and dissi-pate more heat, resulting in a coolergrid.

Newer types of tubes, such as the 43,48, 2A5 and 42, which employ cathodesrequiring a large amount of heat, aresubject to grid -emission troubles due tothe proximity of the control grid to thecathode. To overcome this difficulty,heat radiators are mounted on the topof the grid side rods to help dissipatethe heat which causes grid emission.

In addition, the use of new materialsfor the grid wires themselves has pro-duced a cooler grid. As one example,the 59 employs wire, which has beencarbonized, for the grids adjacent to thecathode. The carbonized metal reducessecondary emission and radiates heatso as to maintain the grid at a temper-

ature low enough to prevent excessiveprimary emission.

The practical effect of reduced gridemission is that the tube dissipationcan be increased. Higher internal dis-sipation means higher output from thetube and better performance from theradio set.

Another practical benefit to the setengineer resulting from a reduction ingrid emission is the feasibility of oper-ating tubes such as the 2A5 with resist-ance coupling, since the use of moder-ate values of resistance in the grid cir-cuit of these tubes will not cause a lossof bias due to grid emission. Unlessgrid emission in certain output tubes isheld to a low value, their use is limitedto transformer -coupled circuits.

Rigorous Tests for Every Tube

A more stringent and exacting se-ries of tests has been initiated for eachtube type. Every tube leaving the fac-tory is subjected to these tests. Eachtube must conform to the standards ofquality and uniformity established forthat type.

Noisy tubes are frequently the sourceof trouble in receivers after they havebeen put in use by the customer. Whilethis trouble has often been blamed uponman-made static, in many cases thetubes themselves were the cause. Toguard against noisy operation in pre-liminary amplifier and detector applica-tions, every Radiotron and Cunninghamtube of the types so employed receives anoise test in high -sensitivity receivingcircuits in addition to numerous otherelectrical tests. In this way, thosetubes which might cause trouble areeliminated.

Representative quantities of tubes,selected at random from production, arelife tested. Characteristic checks madefrequently during the life test revealhow well the tubes are standing upunder actual operating conditions. Inthis way it is possible to determine theserviceability of each type. By con-trolling manufacturing processes in ac-cordance with the results of these tests,each tube leaving the factory is particu-larly fitted for operation under the con-d!tions for which it was designed.


The improvements in tube designand construction which have been madein the past enable the radio set engineerto achieve better set performance. Theimprovements which will be made inthe future will make possible even great-er advances in receiver design. Con-

sequently, it is helpful to the radio setengineer to be conversant with thelatest design features of all radio tubetypes, since these features provide bet-ter performance capabilities which canbr, readily capitalized by the set engi-neer.


Join the ORSMAEver since the appearance of the com-

mercial radio broadcast receiver as ahousehold necessity, the Radio ServiceMan has been an essential factor in theradio trade; and, as the complexity ofelectrical and mechanical design in re-ceivers increases, an ever -higher stand-ard of qualifications in the Service Manbecomes necessary.

The necessity, also, of a strong asso-ciation of the technically -qualified radioService Men of the country is forcingitself upon all who are familiar withradio trade problems; and their re-peated urging that such an associationmust be formed has led us to under-take the work of its organization.

This is the fundamental purpose ofthe OFFICIAL RADIO SERVICEMEN'S ASSOCIATION, which is not amoney -making institution, or organizedfor private profit; to unite, as a group

with strong common interests, all wellqualified Radio Service Men; to makeit readily possible for them to keep upwith the demands of their profession;and, above all, to give them a recog-nized standing in that profession, andacknowledged as such by radio manu-facturers, distributors and dealers.

To give Service Men such a standing,it is obviously necessary that they mustprove themselves entitled to it; anyService Man who can pass the examin-ation necessary to demonstrate hisqualifications will be elected as a mem-ber and a card will be issued to himunder the seal of this Association, whichwill attest his ability and prove hisidentity.

The terms of the examination havebeen drawn up in co-operation with agroup of the best-known radio manu-facturers, as well as the foremost radioeducational institutions.

The following firms are co-operating with usin formulating the examination papers.THE CROSLEY RADIO CORPORATION, CIN-

CINNATI, OHIO.Mr. D. J. Butler, Service Mgr.

ORIGSBY-GRUNOW COMPANY (Majestic), CHI-CAGO, ILLINOIS.Mr. L. G. Wilkinson, Service Mgr.

STROMBERG-CARLSON TELEPHONE MFG. CO.,ROCHESTER, N. Y.Mr. E. S. Browning, Service Mgr.

COLIN B. KENNEDY CORP., SOUTH BEND,IND.Mr. II. F. McNamee, Prod. Mgr.

RCA -VICTOR COMPANY, INC., CAMDEN, N. J.STEWART-WARNER CORPORATION, CHICAGO,

ILLINOIS.Mr. T. N. Golten, Service Mgr.

The schools who have consented to net as anexamination board are:International Correspondence Schools, Scranton,

Penna.Mr. D. E. Carpenter, Dean.

RCA Institutes, Inc., New York, N. Y.Mr. 0. D. Whelan, Director.

Radio Training Association of America, Chicago,III.

Mr. A. 0. Mohuapt, President.Selesd of Engineering of Milwaukee,

Milwaukee, Wis.Mr. W. Werwath, President.

Radio Division, Coyne Electrical School,Chicago, Ill.Mr. H. C. Lewis, President.

For the convenience of Service Menwho do not have time to answer thequestionnaire, an Associate Member-ship has been formed. Service Menmay become Associate Members bysimply filling in a form telling theirexperience and qualifications. Identifi-cation cards are furnished to Full andAssociate members.

If the candidate does not pass thisexamination the first time, he may ap-ply for another examination three orsix months later.

There is absolutely no cost attachedto any service rendered by the Asso-ciation to its members, no dues, no con-tributions.

If you wish to be-come a member justwrite your name andaddress on a postcard and mail it tous. Specify if youwish to becomean Associate or aMember.

OFFICIAL RADIO SERVICE MEN'S ASSOCIATION, Inc.98VT Park Place New York, N. Y.

MODERN VACUUM TUBES

WHAT ARE YOU DOING

ABOUT YOUR FUTURE

IN RADIO?...prepare now forthese adventurousexciting branches

Aircraft Radio . . . Broadcast

Station or Studio ... TalkingPictures . . . Direction Finderor Radio Compass ... Disc andFilm Recording . Servicing

of Home Entertainment Equip-ment .. . Television.

RADIO offers 7 interesting branches foryou to choose from, each filled with

possibilities of adventure, advancement,excitement!

It is easy to learn these thrilling breachesof radio at the RCA Institutes, through ad-vanced methods, and association with thelargest, most complete research laboratoryin the radio industry. No rubber stampcourses at RCA Institutes-the man whoalready has a radio background can entera course fitted to his particular needs. Thefour resident schools -at New York,Philadelphia, Boston and Chicago - offerelementary and advanced courses in practi-cal radio. Courses constantly revised toinclude latest developments.

Control room inside a great broadcast studio

Look! Short scare operation. . . from ground to airplane!

Win Radio ScholarshipIf you cannot attend the resident schools,RCA Institutes Extension Courses enableyou to study at home. Special laboratoryequipment furnished. Outstanding gradu-ates of extension courses become eligiblefor free scholarship at nearest residentschool. All tuition costs moderate. Sowrite today for catalog, full details. Thecoupon makes it ea.y.

RCA INSTITUTES, Inc.r

RCA Institutes. Inc.. Dept. RSA 31.75 Varick St., New York. N. Y.Gentlemen: Please send me your GeneralCatalog. I am checking below the phase ofradio in which I am particularly interested. Aircraft Radio Broadcast Station or

Studio Talking Pictures Direction Finder and

Radio Compass

Disc and FilmRecording

Servicing HomeEntertainmentEquipment

Television

Name

Address

Occupation Age

AFTER athorough sur-

vey of all radiotube s tles and allanalysis of the reasonfor senior calls, we has:found I lilt 1111)111 I ev"rbefore t the sm., iceman be-ing (tilled utom for tubereplacement and lulu. oh....We are tamoughly confident teatthere ire !Nal...Is of intellrgent.Trarettom. in all Parts of the worldwho understand the tiesitabiliiy ofknotting just what the tithe char-acteri are when the lute isput in tour socket. Therefore.we are selecting and appointingCERTIFIED TRIAD SE1LV:CE-MEN Ir every corner of the globe.to ensue you to get the 11,1'a-m-ance you pay fur. And we has('decided to sell these special tullesthrough these rep bible men, ex-clusively.

SERVICEMEN-WRITEFOR OUR SALES

PROPOSITION

MODERN VACUUM TUBES

A APTUBESThe LONG LIFE TUBEof Universal Satisfaction

TYPE 1 -244 -ACT -224 -AP is an A. C.four element. 91,,grid tube. for rad,frequency stages invial rinadts. Ittepa,heater type anti otter:*directly on A C.Heater Fil. Volts.Heater Fil. Amps. I

Plate Veils Mar 1 I-5 prong Y type base

TYPE T-227T-227 .8. C. deter:or amplifier, sepal:quick heater type.limiter Fit. Volts.. -Deafer

Ell. Amps.Detector Plate Volt- ;

Used as amplifierPlate Volts...911 I.

5 prongYPE'V I1-245

s pe baseT

T-2IS is a louver am-plifier for use in theoutput of receivers as-signed especially for itsuse. (Not Interchange-able with T-171 or

Fit Volt, 2 5Fit Mops ..1.5Plate Volts ....1x11-2511Negathe (Dial

Dias 83-50TYPE 1-280

1-2011 is a heavy dutyfull wate rectifier tubefor use In A. C, re -:elvers or A. It, andI' eliminators.I -it. Vohs 5.0Ell. .Mops 2 0A C. Volts TunIl tl A 125

TYPE 1.171 ANDT17IA

'I'-171 T-17IA pow-er amplifiers for use Inlast audio sieges onlyWill handle great y:time without distortsEll. VoltsT -7I Fil. AuntsT71.8 Fit Amps

V P . 9

TRIAD

TYPE T -I I2AT -112A output amplifiert uttes are designed furuse In the last audiostages of battery oper-ated and A. C sets.Fit Volts 5 0T-12 F17. Amps..... 5T-12.8 FII. Amps. .15Plate Volts 90.180

TYPE T-551T-551 Is a at-reen gridvariable mu tube de-signed to eliminatentss talk and distortion

and reduce static to a

minimum. interchange-able with T-224 in mostcircuits.If eater Vols 2.5Heater Current .1.75Plate Volts 27.0Screen Volts lluGrid Illas Volts... --3Plate Current (ma.) 0.5TYPE 1-247 PENTODET-247 is a New SuperPower Audio Amplifierwith extremely highamplification factor andpower output.Fil. Volts 2 5Fit. Current 1 5Screen Volts 250Plate Volts 250Grid Bias Volts 16.5Plate Current

Dna.) 32.5Power Output

Walls 2 5

TYPE T-235T-255 Is a Variable MuSemen Grld Tube simi-lar to the type T-551.Type T-235 is especial -Is adaptable to setswith automatic volumecontrol.Heater Volts 2.5lieat er Current ....1.75Plate Volts 250s/reen Volts 90()rid hies Volts... -3Plate Current

(ma.)

TYPE T -201AT-2iilA is a standardbattery operated tubefur use as detector andamplifier in any circuit.loll. Volts 511Fit. Amps 25Plate Volt...45 & 155

TYPE 1-226T-226 A. P. Amplifierfor radio frequency andaudio stages. Raw A.C. 61 used on the file-tnent.Fil. Volts 1 5Fit. Amps 105Plate Volts 90-135

TYPE 1-222 DCT-2221/17 is a D. C.four element screen gridtube, for use In radiofrequency stages ofspecial circuits.Fil. Volts 3 3Ell. Amps 132Plate Volts 135Control Odd

Illas I to 1.514.0,n fIridCELL AND BATTERY

TUBES FOR DRYOPERATIONTYPE 1-230

A general purpose de-tector and amplifiertube for dry cells andbattery operation.Fit. Vols 2

Fit. Current .0(1Plate Volts 941

Grid Volts -4.5Plate Current (ma.) 1.8

TYPE T-231A power amplifier de-signed for dry cell andbattery operation.Fit. Volts 2Ell. Current.. .13 amp.Plate Volts 135Grid VoltsPlate current Dow) 0.8Undistorted POW.

Output (al% I 150

Manufacturing CompanyTelevision Mfg. Co.

This t partial list of tub:, manufactured by TRIAD

MODERN l'Ac1111 TUBES

Radio's Greatest Servicing BookThe Most Complete Directory

of Radio Circuit Diagramsin One VOLUME

of over 2300 Pageswith Extra Heavy Cover

- Loose Leaf Bound

Buy This Big Volume on our New

DEFERRED PAYMENT PLANHere are two of the most surprising announcementsthat .e have ever made to the radio trade end weknow Sisal it is such good news that every radio manwill be greatly enthused.FIRST-that the three editions of the OFFICIAL

RADIO SERVICE MANUALS have nose been com-bined into one big volume of over 2.3u0 pages.

SECOND-that this new single volume of consolidatedradio circuit diagrams and complete radio servicingcourse can be hands on a deferred' PaMod Plan-and at a big saving for you.

It is needless to say how valuable the OFFICIALItADIO SERVICE MANUALS have been to membersin every branch of the Radio Industry, and how manythousands of each edition have been sold to menu-racturers, jobbers. dealers. Service Men and experi-menters. But we mut emphasize this one fact: Ser-vice Men now realize that. they are tremendously handi-capped without the full set of Gernsback Manuals. Somuch so. that those who have purchased only one ortwo volumes. are NOV ORDERING THE MISSLNGBOOKS.The complete hook glees you a volume of over 2.300pages with over 5,500 diagrams, chart: and photos.There are absolutely no pages or illustrations or dia-grams duplicated. There is no radio book publishedtoday which Is so modern. up -to the minute. and whichcontains --ty much useful information as Is to be foundIn this single voltam.. It Is a book that will outlastany other radio book in print. The book measures9" wide, 12" long. 4,42" thick.

Included In this volume is a complete radio ser-vicing course. This roar, covers every step needed tolearn the servicing business ... from starting in busi-ness ... materials needed . . and how to go aboutservicing receivers and repairing other radio equipment.This course In Itself. is actually worth the price ofthe entire hook.

Mail Coupon Today!fERNSBACK PUBLICATIONS. Ins..96-98 Park Place. New York, N. Y.Gentlemen:

In accordance with your Special Offer. 1 encloseherewith 0:L on a: first payment toward the One -Volume Radio Manual. Please forward It to mepromptly. Upon receipt of the hook, I 'hall payrames, romnany $:". 00, Thirty slays later I shallsend you 0:1 Isis. and sixty slay: after ruse list ofhooks. 1 shall send you my last payment of 93.00.

If you want to take advantage of the Special Dis-I

of 10;i,. remit only $12.60 with this coupon.

Name

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ii l

Our new plan now enables ever, radio man to gelthis single volume-a Complete Directory of Il Cir-cuit Diagrams. of over 2.300 pages. on deferred pay-ments. You can order this book immediately-get ItIn a few days, and use it while you are doing nor-rlr log work. You can make the first few calls payfor the entire cost of the book.For you to get this book Is quite simple and it lasent to yOU as soon as your order Is received. You Pa/for it In small monthly amounts which can be takenfrom your earnings. If you were to buy the threevolumes separately, the total cost would be $17.00. in-cluding the supplements.Now you can get the

ism OFFICIAL RADIO SERVICE MANUAL. withSupplement-,

1932 OFFICIAL RADIO SERVICE MANUAL, withSupplements.

and the 1933 OFFICIAL RADIO SERVICE MANUALComplete

at a big saving.THE SPECIAL NEW PRICE FOR ALL THREE

MANUALS. WITH SUPPLEMENTS. IN ONEVOLUME. WITH HEAVY BINDER

IS ONLY

$14.00You buy this book this way-Send $3.00 with order-Pay $5.00 to Express Company upon receipt of book.Send $3.00 thirty days alter receipt of book.Send $3.00 sixty days after receipt of book.Total $14.00.IF THE ENTIRE AMOUNT IS SENT WITH YOURORDER WE WILL ALLOW YOU A 10% DISCOUNT.

THIS CAN BE DEDUCTED FROM YOURREMITTANCE.

IMMEDIATE SHIPMENT

Over 2,300 Pages

Over 5,500 Illustrations

THIS IS THE GREATESTSINGLE VOLUME RADIOBOOK IN PRINT TODAY

GERNSBACK PUBLICATIONS, Inc.96-98 Park Place, New York, N. Y.

k111444144441144144144414414444444441111441441

tl2 MODERN VACUI..11 TUBES

Here you will find other titleswhich are included in the Seriesof the book you are now reading

Presented on this page are the new books of the RADIO -CRAFT LIBRARY-the most com-plete and authentic set of volumes treating individually, important divisions of radio. Each bookhas been designed to give radio men the opportunity to specialize in one or more of the popularbranches of the industry. The material contained in these books will increase your knowledge:you will find them a real help in your work and they will contribute to your money earningcapacity. Read these books during your spare time at home.

The authors of these books are well-known to everybody. Each one is an expert radio man:an authority on the subject-each is thoroughly familiar with the field which he represents.This is perhaps the first real opportunity that you have ever had to build a radio library ofbook. that ate authentic, right -up-to-the-minute and written so that they are easily digested.

Book No. I

RADIO SET ANALYZERSAnd How To Use Them

With Full Instructions and De-scriptions of Set Analyzers, Tube

Checkers. Oscillators. Etc.By L. VAN DER MEL

Book No. 2

MODERN VACUUM TUBESAnd How They Work

With Complete Technical Data onAll Standard and Many Special

TubesBy ROBERT HERTZBERG

Book No. 3

THE SUPERHETERODYNE BOOKAll About Superheterodynes

How They Work. How to Build andHow to Service Them

By CLYDE FITCH

Book No. 4

MODERN RADIO HOOK-UPSThe Best Radio Circuits

A Complete Compendium of theMost Important Experimental and

Custom-built ReceiversBy R. D. WASHBURNE

Book No. 5

HOW TO BECOME A RADIOSERVICE MAN

How To Get Started and How ToMake Money in Radio Servicing

By LOUIS MARTIN

Book No. 6

BRINGING ELECTRIC SETSUP TO DATE

With Pentodes. Multi -Plus. Dy-namic Speakers-Complete Inform-

ation How to Modernize A.C.,D.C. and Battery Operated

ReceiversBy CLIFFORD E. DENTON

Book No. 7

RADIO KINKS AND WRINKLESFor Service Men and

ExperimentersA Complete Compendium on the

Latest Radio Short -Cuts andMoney -Savers

By C. W. PALMERBook No. 8

RADIO QUESTIONS ANDANSWERS

A Selection of the Most Importantof 5.000 Questions Submitted by

Radio Men During the Courseof One Year

By R. D. WASHBURNE

Book No. 9

AUTOMOBILE RADIO ANDSERVICING

A Complete Treatise on the SubjectCovering All Phases from Installing

to Servicing and Maintenance

By LOUIS MARTIN

Book No. 10

HOME RECORDING AND ALLABOUT IT

A Complete Treatise on Instan-taneous Recordings. Microphones.Recorders. Amplifiers. Commercial

Machines, Servicing. etc.By GEORGE J. SALIBA

Book No. IIPOINT-TOPOINT RESISTANCE

MEASUREMENTSThe Modern Method of Servicing

Radio ReceiversBy CLIFFORD DENTON

Book No. 12

PUBLIC ADDRESS INSTALLATION AND SERVICE

Modern Methods of Servicing andInstalling Public Address Equipment

By J. T. BERNSLEY

ALL BOOKS UNIFORMThe books In the new RADIO -CRAFT LIBRARY are all scruffy up-to-date and written by men who know theirPubiect,. The volumes are all uniform Sill', I; s 9 Inches, and contain on an average from 50 to 120 illustrations.Each book is printed on fine book paper

Big Discount OfferedIn order to make it possible for every -one to buy these books, the fifty (50) cents price hasbeen made uniform for all volumes. You can buy these books separately, but you should takeadvantage of our special offer:

WHEN FIVE (5) BOOKS OR MORE ARE ORDERED DEDUCT 20%FROM YOUR REMITTANCE

Simply fill in the coupon below. and mail it to us together with your remittance. Checks, stampsor money orders accepted.

Clip Coupon and Mail TODAY

GERNSBACK PUBLICATIONS, INC.96-955T Park Place, New York, N. Y.I have circled below the numbers of books in the RADIO -CRAFT LIBRARY, which youare to send me, and have deducted 20% for ordering five (5) hooks or more. I haveincluded my remittance in full, at the price of 50c each, when less than five books areordered.

The amount of my remittance is________(Stamps, checks or money orders accepted.)Circle numbers wanted: 1 2 3 4 5 6 7 8 9 10 11 12

Name Add -t-,City State AR


hall trainyou athomelofili a A.6".'

413169PAYRadiojobJ. IC. Smith, President. Nes!lona! Had, Institute. the menwho has directed the HomeEtude lrainimt of noire menfor the Radio induntry thanany other man In America.

Free BookTells Mow

Mall Coupon!

Get my big FREE book on the opportunities inRadio. Read how quickly you can learn at homein your spare time to be a Radio Expert-whatgood jobs my graduates have been getting-realjobs with real futures.

Many Radio Experts Make $50 to $110 a WeekOver 800,000 jobs have been created by Radio'sgrowth, and thousands more will be created by itscontinued development. Many men and young menwith the right training-the kind of training Igive you in the N. R. I. course-have stepped intoRadio at two and three times their former salaries.

Many N.R.I. MIDIS Rave made 8200 to SteseIn spare time while learning

The day you enroll with me I send you material whichyou should master Quickly for doing 28 Jobs, commonIn most every neighborhood, for sparettme money. I giveyou the plans and Ideas that have made 8200 to $1,000for N. It. I. students In their spare time while study-ing. My course Is famous as the course that paysfor Itself. I have doubled

Aircraft Radio Included and tripled theTalking Movies, Television,

Special training in Talking Movies Television Find oesut aboutTelevisionanti home Television experiments, Radio's use

Salaries ofin Aviation, Servicing and Merchandising Sets,Broadcasting, Commercial and Ship Stations are this tested wayincluded. I am so sure that N. It. 1. can trainyou satisfactorily that I will agree in writiltsto refund every penny of your tuition if you

t,are not satisfied with my Lessons and Instrtie-ti 11 Sir, 0, uiom t

64.page Book of InformationFRI'Get your copy today. It tells you whereRadio's good jobs are, what they pay,tells you about my course, what otherswho have taken it are doing and making.Find out what Radio offers you withoutthe slightest obligation. ACT NOWI

NEW Radio Equipmentfor Broad Practical ExperienceGiven Without Extra Chargevv,th this equipment yell mirk out many of thethings ton read in textb4niks. From it pin getthe experience that tells an expert from a be-ginner. In a short time you hare learned whatWould take years to learn in the field. Youmake experiments illustrating the importantprinciples lu the 2$ beat known receiving sets.

J. E. SMITH. PresidentNational Radio Institute, Dept. 2ED7Washington, D. C.

Dear Mr. Smith: Send me your freebook. I understand this request does notobligate me and that nu salesman will call.

NAME

ADDRESS

CITY STATE


The Radio Serviceman's Supply House

WHERE

QUALITY SERVICELowest Wholesale Prices

Are CombinedComplete Lines of Finest Quality, New MerchandiseCarefully Selected for You from the Offerings of

the Most Reliable, Standard Manufacturers

Test Equipment, Tubes, Batteries, Repair Ports, Accessories of all Kinds.Public Address, Lighting Fixtures, Electrical Supplies, and many otheritems to make money for you,are carried in stock-always ready for you.

Fastest, Most Reliable ServicePractically every mail order shipped same day

VERY PROMPT, COURTEOUS, HELPFUL COUNTER SERVICE

Men from Chicago and vicinity will find us conveniently locatedwith plenty of parking space all times of every day.

Get Your Copy of Our New 1932 Serviceman's Price Guide.Send for It NOW'

Radolek Co. 4)41'444,502 Canal Station,Chicago-

Please send me without °blip°. CoUpONtion your Serviceman's Supply Book.NameAddressCoy State

Ell KOMI ZVI II ZrellA GOLDEN OPPORTUNITYFOR ALERT RADIO MEN IN

THE NEXT GREAT INDUSTRY

SERVICE MANUAL

Official Air

1352 Pages

Over 600

Illustrations

9x12 Inches

Flexible, Looseleaf

Leatherette Cover

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., tu, _t 1,1

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4 r! r, a I ,r tgl,t,lent, rlt.

m- lit ricir I

"I advice wiling and progressive men to go

Into the airconditioning business during thenext few years; because, th,. without a doubt.Is the coming industry in this country. Thous-ands of small firms will spring up. undertakingto air-condition private halms. small Inc., ne,offices. factories. etc. We are not going to

tear down every building in the United States

immediately. It will be a gradual gr,cath het

small installation firms will trcond ,n smallhouses. and evrn single offs; in small bodd-legs."

This Is only partial proof or the certain surcess ofthis nets Held. Further assurance is that engineeringschools have already added many Important courses onair rontlitioninat to their regular curriculum. Arehltectsand building Contractors are giving conblerable thoughtto installation of this equipment in structures whichare now being planned and built. The beginning ofthis business will probably be similar to the autoand radio industries. but in a has short Years it willsurpass these two great fields.

Conditioning Service ManualThe OFFICIAL AIR CONDITIONING SERVICE 'MANUAL la being edited by

L. K. Wright. who is an expert and a leading authority on air conditioning andrefrigeration. He is a member of the American Society of Refrigerating En-gineers. American Society of Mechanical Engineers. National Association ofPractical Refrigerating Engineers: also author of the OFFICIAL REFRIGERATIONSERVICE MANUAL and other volumes.

In thin Air Conditioning Service Manual nearly every page is illustrated;every modern installation and Individual part carefully explained; diagram, fur-nished of all known equipment; arterial rare given to the servicing and installationend. The mob neeced are Illustrated and explained; there are plenty ofchart§ and page after page of service data.

Remember there is a big opportunity in this new field and plenty of moneyto be made in the servicing end. There are thousands of firms selling Installationsand parts day ar.d this equipment must be cared for frequently. Eventuallyair conditioning systems will be as common as raillri: and refrigerators in homes,Mitres and Industrial plants. Why not tart now-inereasa your earnings with afull- or spare -time service business.

Here are some of the chapter heads of the OFFICIAL AIR CONDITIONINGSERVICE MANUAL:

CONTENTS IN BRIEFHistory of Air C !r! ir !!!!.... : I n:' !.,..,t1..:i Lras; Methods of Refrigeration:

Elector System of It, Iris, r r .. i'rt,i,ro-.,1; Sila-rn of Refrigeration; Refrig-erants; Lubricating Oil,: Liquid Throttle Deck,: ; Servicing Expan- ion and FloatValves; Servicing Refrigerating Sy,tems ; Control Devices; Thermodynamics of AirConditioning: Weather in the United States; The Field of Air Conditioning:Insulating Materials; deal TransmIs.don Through Walls; Complete Air Condition-ing Systems; It:stir.? rag Requirements for the Home, Small Store. Restaurant;Layout of Duct St .tuns:Ill.,: S!.rrilr, Up Se -rem; Orivr..lini, and livrvIrIng AirCondit 1, ,t, it, t. Si , t,,,, :.Air I' i' r.,' ',,,. Ver:a l. i , r, a .and N. !.. 1!! irtlirlir irti.; lirsirrs;Portal.',. F'. . tri. ll, 1.! !CI. .. .nr ! It !:, a' I. ..: \u a, ,, i. !loc.. lit !r- : .sirConde, -min:;I 'rrit her lia.:1.1! r- S'..rr int .1.4: W.,rn, A , t-ta -.arams. l'irr r.il Con-ditioning I 'nit etc

Send remittance of $5.00 in form of check or money orderfor your rosy of the OFFICIAL AIR CONDITIONING SER-VICE MANUAL. Register letter if It contains cash orcurrenry, THE MANUAL IS SENT TO YOU POSTAGEPREPAID.

GERNSBACK PUBLICATIONS, Inc. 96-98 VT PARK PLACENEW YORK, N. Y.

$350

There's plenty of Servicing 'Material

in the NEW 1934 ManualiiF.RNSBAC,K :Tanuals in Contents of the 1934 Manual

the Mdd been slitywn by the i lu1. in Briefthat the tetat sales of the tirst throcIZA1.111) SERI'ICE INIANt ALS. in- C.iorame and <61,/, etimplcto

than r tiotori in itny MANUAL. Not merelyiiluding the iky- ctiNsitt.IDATE'l) ED IHN, the sli--.111i /1,/014Up5 a I ft 5n 1/16nli but elms-exoeed ,st,noti copi,s. Radio Service Men Si; (co-.,I,part, layouts, bncition, of

lethell -2. engaged in various hranche.z of for pearticaill all sets.U(110 knot; the iwpottunce -of such books, and as an aid in ,horking tubes ant! wiring.

how they nliv:t fotr upon them fur reliable ob A i valu, iron, fried late- irequorleY tree,}man., us. -1 //l/I/urh,/,:lJdVneS. With the maninformation. \Vlietia'r for puhlic-iiiiiiros ia04,4eitotigi,rs. soUOt..1.an, an to 0,,-.-eot

tithe information oi a circuit diagram, the rst,, trouhloshnoting tuggestiona andmatern-il needed bs cortain to lie found in ono pokca,e hr tnr nianufortoror,' ownengin, i other st., its auth,ntit -dope"right Iron, heado,arters.al V E.., of .01 part: indicated dire'lly onall diaoAms.al . .11.0 midgets.

P

'r rir,ears.It ar.trol ,)..items,

el A . ropleto inriallat ion of radio tube data.totem Id and the many beat types. Sm!...n In t..st equipment. nnniy.tort. nlogrun, and ctilervalu-able irPI A ii -1 Amerloart broadratt sta-tion, ,oth in ktlooyelo,: ex.

/11. IN 1. , I,1 IP b/./ /1///1 and cht, king t. -'tHat, and in tali rereinon

,,p 0,, tic ti and Act Plet Snook..., Itoau t /A./

a N., , ,.ol, r.ie information in

Vet

& A', ..t, 11.011 of any diOrnms:/// pp, I. .nN of tho pr!,,nu!

..aa, ir tho 1934 MAN L'A(I . antre

I, ,"'red mattor inner,oak ,n t., ../// I./ Pod anytiiii 9

rtain -- sort., arDblem 1:14t4iit.)

GERNSBACK PUBUCATIONS, Inc. !i`j 'IT PARKNEW YttRK, N. A.

modern vacuum tubes - worldradiohistory.com...modern vacuum tubes 5 cloud over or around it. the...

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