for beginners - museum of yesterday...force that the friction heats the pipe to...

GERNSBACKS EDUCATIONAL LIBRARY N2 3

LTZENTINGCURRENT

FOR BEGINNERSItHONE EX PIRAVMS

GENERATORSMOTORSOHM'S LAW

HOUSE WIRING SYSTEMS

APPLIANCESTRANSFORMERS

. INDUCTANCESA.C. INSTRUMENTS

IADIO PUBLICATIONS,101 HUDSON ST NEWYORK.N.Y

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scientific and radio literature. Since that time, many millions ofGernsback magazines and books have been distributed and read bypeople all over the globe.

Recently, Hugo Gernsback decided to place upon the market anew, popular priced series of books under the name of GERNS-BACK'S EDUCATIONAL LIBRARY. It is the intent of thepublisher to continuously add books to the library, from time totime, under various titles. These books will cover a great manysubjects, which will not necessarily be restricted to radio or sci-ence, but which will encompass many other arts.

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Don't forget either, that Gernsback booksand magazines always have given you yourfull money's worth. The present series ofbooks again proves this. Never in the historyof technical publishing have you been ableto buy so much for so little money. The an-swer to this is in turning out a greater num-ber of books and in large quantities.

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Title: HOW TO READ RADIODIAGRAMS, Book, 7

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Book 8(Watch the List Grow)

(Copyright 1938, by H Gernsback)Printed In II. S.

Four Recent Additions to theGERNSBACK'S EDUCATIONAL LIBRARY

11EGINN.er, RADIO I.VIC/ 'OMAR!

No. 5-BEGINNERS' RADIO DICTIONARYAre you puzzled by radio language? Can you define frequency? Kilocycle?Tetrode? Screen grid? Baffle? If you cannot define these very common radiowords and dozens of other, more technical, terms used in all radio maga-zines and Instruction books. you need this book in your library. It's asmodern as tomorrow-right up to the minute. It tells you in simple lan-guage just what the words that puzzle you really mean. You cannot fullyunderstand the articles you read unless you know what radio terms mean.This Is the book that explains the meanings to you. Can you afford to bewithout it. even one day longer?

No. 6-HOW TO HAVE FUN WITH RADIOStunts for parties, practical lokes, scientific experiments and other amuse-ments which can be done with your radio set are explained in this fascinat-ing volume. It 'ells how to make a newspaper talk-how to produce silent

music for dances-how to make visible music-how to make a "silentradio" unit. usable by the deafened-how to make toys which dance toradio musio-sixteen clever and amusing stunts in all. Any of these canbe done by the novice, and most of them require no more equipment thancan he found in the average hrme. Endless hours of added entertainmentwill be yours II you follow the instructions given In this illustrated book.

eou t11 KO. TO RIO*t, too o

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No. 7-HOW TO READ RADIO DIAGRAMSThe symbols collation's' used in radio diagrams are presented in this book-with pictures of apparatus they represent and explanations given an easymethod to memorize them. This book, by Itobert Eichberg, member of theeditorial staff of RADIO -CRAFT, contains two dozen picture wiring dia-grams and two dozen schematic diagrams of simple radio sets that you canbuild. Every diagram Is completely explained in language which Is easilyunderstood by the radio beginner. More advanced radio men will be Inter-ested in learning the derivation of diagrams, and the many other interestingfacts which this book contains.

No. 8-RADIO FOR BEGINNERSHugo Gernsba2k, internationally famous radio pioneer, author and editor.whose magazines, RADIO AND TELEVISION and RADIO -CRAFT are readby millions. scores another triumph. Beginners who read it get thoroughground work in radio theory, clearly explained in simple language, andthrough the use of illustrations. Analogies make things as simple as "2+2is 4." It contain, diagrams and instructions for building simple sets, suitablefor the novice. If you want to know how transmitters and receivers work. howradio waves traverse space, and other interesting facts about modern com-munication. this is the book for youl

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Here Are Additional Titles in the FamousGERNSBACK'S EDUCATIONAL LIBRARY:

No. 1-HOW TO BUILD FOUR DOERLESHORT WAVE SETS

Literally thousands of radio fans have built the formula DCERLE ShortWave Radio Receivers. So insistent has been the demand for these receivers.as well as construction details, that this book has been specially published.Contains EVERYTHING that has ever been printed on these famous receiv-ers. These are the famous sets that appeared In the following issues ofSHORT WAVE CRAFT: "A 2 -Tube Receiver that Reaches the 12,500 MileMark." by Walter C. Merle (Dec., 1931 -Jan., 1932). "A 3 -Tube 'SignalGripper'," by Walter C. Doerle (November, 1932). "Deer 'e '2 -Tuber'Adapted to A. C. Operation" (July, 1933). "The Doerle 3 -Tube 'Signal -Gripper' Electrified." (August. 1033) and "The Dierie toes 'Buzu-Spread'(May. 1934).

No. 2-HOW TO MAKE THE MOST POP 7LARALL.WAVE 1- and 2 -TUBE RECEIVERS

There has been a continuous demand right along for a low-priced hook forthe radio experimenter. radio fan. radio Service Man. etc.. who wishes tobuild 1- and 2 -tube all -wave sets powerful enough to operate a loud -speaker.This book contains a number of excellent sets, some of which have appearedin past Issues of RADIO -CRAFT. These sets are not toys but have been care-fully engineered. They are not experiments. To mention only a few of thesets the following will give you an Idea.The Megadyne 1 -Tube Pentode Loudspeaker Sot. by Hugo Gernsback. Electri-fying the Megadyne. How To Make a 1 -Tube Loud -Speaker Set. by W. P.Chesney. How To Make a Simple 1 -Tube All -Wave Electric SR, by F. W.Harris. How To Build A Four -In -Two All -Wave Electric Set, by J. T.Bemsley, and others.

1 Oc Each

No. 4-ALL ABOUT AERIALSIn simple, understandable language this book explains the theory underlyingthe various types of aerials; the inverted "L." the Doublet. the DoubleDoublet, etc. It explains how noise -free reception can be obtained, how low.impedance transmission lines work; why transposed lead-ins are used. It aloesIn detail the construction of aerials suitable for longwave broadcast receivers,for short-wave receivers, and for all -wave receivers. The hook is written insimple style, Various types of aerials for the amateur transmitting stationare explained, so you can understand them. It eliminates, once and for allthe confusion about the type of aerial to choose for best broadcast and short-wave reception. Nor the thousands of radio fans, both short-wave aid broad-cast, who wish to know lust what type of antenna they should use and why.this book has been especially published.

BOOKS ARE ALL UNIFORMEvery book in the GERNSBACK'S EDUCATIONAL LIBRARY has 32pages-with illustrations varying from 30 to 66 in number. Each ntlevolume contains over 15,000 words. POSITIVELY THE GREATEST10c VALUE IN RADIO BOOKS EVER OFFERED TO THE PUBLIC.

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Alternating Current for Beginners 3

When the piston is pulled back, thevalve opens and the piston has nodriving action on the water. Eachleft stroke, therefore, forces waterthrough the system always in thesame direction, and we have a directcurrent (of water). The large pipesoffer little opposition to the flow ofthe water. The small one offers highresistance to the flow of water. Andby a little stretch of our imagination,we can conceive of the flow of waterthrough the small pipe with suchforce that the friction heats the pipeto brilliancy-representing the light-ing of the electric lamp filament.

Ohm's LawIn the hydraulic analogy, mechan-

ical energy is expended in drivingthe water through the pipes. In theelectric circuit, chemical energy isexpended in driving electricitythrough the wires. The driving forceis called voltage, or electromotiveforce (e.m.f.). The electricity flowingthrough is called amperage, or simplycurrent. In the analogy, the drivingforce may be called pressure, whichis analogous to voltage, and the waterflowing through the pipes representthe current, or amperage. In the elec-tric circuit, the voltage may be meas-ured in volts (units of electrical pres-sure) and the current in amperes(units of electrical current). Theresistance is usually measured inohms, which are units of electrical re-sistance. The units are so chosen thata pressure of one volt will cause acurrent of one ampere to flow througha circuit having a resistance of oneohm, This is easy to remember. It isthe basis of Ohm's law, which states

that current equals voltage dividedby resistance. OrAmperes =

Voltsor I = -

Resistance (Ohms)where I is the current (taken fromthe word Intensity), E is the volt-age (from Electromotive force), andR the resistance.

The unit of electrical power iscalled the Watt, W. Neither currentnor voltage alone represents elec-trical power, as we cannot have aflow of current without having adifference of potential or voltageacross the circuit through which thecurrent is flowing. The wattage(power) is equal to the product ofthe voltage and the current, or voltstimes amperes.

For example, in the above illustra-tion where a current of one ampereflows through a circuit having a re-sistance of one ohm under a pressureof one volt, the power expended is(volts multiplied by amperes) 1 X Ior 1 watt.

By algebraic manoeuvering (themechanics of which do not concernus here), Ohm's law may be expressedin several convenient forms:

EI =- E = IR

R.

Eand R =

Since the wattage is equal to Etimes I, and E is equal to IR, then,substituting IR for E, the wattageis also equal to IR times I or PR.That is, W = PR.

4 Alternating Current for Beginners

Or, expressed in another man -E

ner, since W = EI and I = -R

E E2W = E X - or W = -

R RThese formulae are true for directcurrent circuits. For alternating cur-rent circuits another factor enterswhich modifies them. This will be ex-plained later.

ElectromagnetismBefore elucidating the theory of al-

ternating current, suppose we firstbriefly review the fundamentals ofelectromagnetism. When an electriccurrent passes through a conductor,a magnetic field is built up aroundthe conductor. This field will deflecta compass needle when held near theconductor. Fleming's rule states thatwhen the hand grasps the conductor,

as in Fig. 2A, so that the thumbpoints in the direction of the currentflow, the finger tips of the remainingfour fingers will indicate the direc-tion of the magnetic lines of force(magnetic field) around the conduct-or. If the direction of the current isreversed, the lines of force will alsoreverse. By winding the conductoraround an iron core, as in Fig. 2C,the iron becomes magnetized, and wehave an electromagnet. If we graspthe electromagnet so that our fingerspoint in the direction of flow of cur-rent(indicated by the arrows aroundit), our thumb will point to thenorth pole of the magnet. The righthand is used:

Whenever an electric conductor ismoved so as to cut magnetic linesof force in a magnetic field, as, forinstance, in Fig. 2B, a voltage is pro-duced which will cause a current toflow through the conductor. This cur-rent can be measured by a galvano-

-A-

PERMANENTMAGNET

DIRECTION OFMAGNETIC FIELD

\t"

n\C--

CONDUCTOR

MAGNETICLINES OF

FORCE-B-

Fig. 2. Illustrating the effects of electro-magnetism and the principle of generation of electricity.


Fig. 3. Simple apparatus for generating alternating current.

meter G connected to the ends of theconductor. If the motion of the con-ductor is in a downward direction, asindicated by the arrow A, the currentwill flow in the direction indicatedby the other arrows. If either thedirection of motion or the magneticfield is reversed, the direction of flowof the current will likewise be re-versed.

This phenomenon is reversible.When current is passed through aconductor which is placed in a mag-netic field, the conductor will heforced to move bodily through thefield.

This is the elementary principleupon which the action of all classesof dynamo electric machinery (mo-tors and generators) depends. Byrotating conductors in a magneticfield, we can generate an electriccurrent. By passing current throughconductors placed in a magnetic field,we can cause mechanical movement ofthe conductors, as in the rotation ofa motor armature. At present weare interested in the generation ofelectricity.

Generation of Alternating CurrentConsider a single loop of conduct-

ing wire arranged to revolve uponits axis between the poles of a mag-net, as shown in Fig. 3. If the loopis revolved manually, it is found thata voltage is set up on each side ofthe loop; for if wires are carried fromeach of the collector rings by meansof two brushes (shown in the sketch)and connected to a galvanometer,then, as long as the loop continues toturn, a current will flow in the circuit,as shown by the deflection of the gal-vanometer needle. Now consideringone side of the loop, it is obviousthat in every complete revolution themagnetic field is cut twice, the con-ductor cutting the flux (magneticlines of force) first in one directionas it sweeps by the north pole Nand then in the other direction as itsweeps by the south pole S.

The direction of the current in theloop depends upon the direction ofthe magnetic flux and the directionof motion; and thus it is obvious thatthe current generated in either side ofthe loop will alternate in its direction


as the loop revolves, sending a cur-rent in one direction when it is cut-ting the flux from the N pole and inthe reverse direction when it entersthe S pole region. The current de-livered to the outside circuit from thisrevolving loop will therefore changein direction twice in every revolution,and if the loop is revolved at a fairspeed a voltage will be generated(and a current will flow if the cir-cuit is closed) which changes fromplus to minus and minus to plus manytimes a second. This, then, is an "alter-nating" current and the machine is asimple alternating current generator,or alternator.

This principle is presented in an-other form in Fig. 4, which is across-section of Fig. 3 taken throughthe plane XX. Here the loop is shownfrom an end view as it rotates be-tween the poles of the magnet. Atthe right is shown the value of thecurrent generated in the loop as it

travels through different parts of themagnetic field. For example, in theposition shown at 1, because the con-ductor is cutting the lines at rightangles maximum positive current isgenerated; at 2, less current is gen-erated, the amount being proportion-al to the sine of the angle of rotation.This is also represented at 2 on thecurve A - B. When the top of theloop reaches the position 3, no cur-rent is generated, as shown at 3 onthe curve since no lines of force arebeing cut. At the position 4, currentcommences to be generated in theapposite direction, and the A-Bcurve continues down below the zeroline, for negative values of currentand so on. The curve A-B is a sinecurve. It represents one completecycle of alternating current. If theloop rotates GO times per second, a60 cycle current will be generated.

Our hydraulic analogy of this phe-

CROSS -SECTION OF

CONDUCTOR ATVARIOUSPOSITIONS ii<-IN A /8 I 71'7 - -COMPLETE \CYCLE / \ I / \ I I

./ \Ak'

--","3/+

A3 0° :

--/lTIME -N / i \ /

N. / I \ /p ' 5 -*"

90° MAXIMUM POSITIVE VOLTAGE

(AXIS OF ZERO VOLTAGE

)18Ir

I

I

4

270° 5"-MAXIMUMNEGATIVE VOLTAGE

360°7 B

Fig. 4. Illustrating the values and polarity of the alternating current at different positions of tneloop of wire during a complete rotation.

Alternating Current for Beginners

Fig. 5. Hydraulic analogy of alternating current

nomena is illustrated in Fig. 5. Weuse a piston and pipes similar to theone used for the direct current analo-gy, Fig. 1, but for alternating cur-rent the valve is omitted. As thewheel rotates, it forces the piston Palternately in and out of the cylin-der C. As the piston is moved fromright to left, it forces water throughthe pipe circuit in the direction of the

arrow A; as it moved from left toright, the water is forced in the op-posite direction as indicated by thearrow B. It is obvious, then, that thedirection of flow of the water re-verses during each revolution of thewheel and an alternating current ofwater flows through the pipes. At Lis indicated a very small pipe repre-senting the lamp filament as used inFig. 1. It makes no difference whichway the water is forced through thissmall pipe; it offers resistance ineither direction and the friction willgenerate heat.

Effective and Peak ValuesFrom our explanation of the flow

of alternating current, it is apparentthat the current is never steady; itincreases from zero to a maximum,decreases to zero again and then in-creases to a maximum in the reversedirection. To measure this current,it is customary to employ the voltand ampere, just as in direct currentmeasurements, but since the alter-nating current is continually chang-ing, its effective value is made thebasis for measurements. The effective

T -PEAK141.4

VOLTS

0

11I- 144

EFFECTIVE 2H1111:11111

VOLTS1 00

III II .1111

EFFECTIVE 1 R.M.S)OF PEAK VALUE X 0.707

VOLTAGE

PEAK VALUEOF EFFECTIVE (R.M5)VALUE XIAI4

VOLTAGE.

Fig. 6. Effective and peak values of alternating current

8

Fig. 7. In this rectifier circuit, fhe effectivevoltage is 110 volts, yet the condenser C. must

have a peak rating of 155 volts.

value is that value which produces thesame effect as a direct current ofequal value. One ampere of directcurrent causes a certain heating ef-fect. An alternating current thatcauses the same heating effect has aneffective value of one ampere.

The effective value is also calledthe root mean square or virtual value.The sketch of Fig. 6 shows an alter-nating current sine wave. The peak ormaximum value of the voltage is141.4 volts. The effective value isequal to the square root of the aver-age of the sum of the squares of allof the instantaneous values. Roughlycalculated, it is obtained by squaringall of the values at points 1, 2, 3, 4,etc., in Fig. 6, adding the results, di-viding by the number of valuessquared, and extracting the squareroot. Such a calculation reveals thatthe effective value is equal to .707times the peak value; and the peakvalue is equal to 1.414 times the ef-fective value. 1.414 is the squareroot of 2.

If the house lighting circuit israted at 110 -volts, 60 -cycles, that isthe effective voltage. The peak volt-age would be 110 multiplied by 1.414or 155.54 volts. This should be re-membered when working with recti-


fiers for changing alternating to di-rect current. In the simple circuit ofFig. 7, a source of 110 volts A.C.is connected to the rectifier, R, andcondenser, C. If no load is drawnfrom the condenser, the condenserwill be charged to a direct potentialof 155 volts-the peak value of theA.C. voltage. Unless, therefore, thiscondenser is rated for 155 volts (peakvoltage rating) it will break downwhen no load is on the rectifiercircuit.Inductance, Capacity, Power Factor

INDUCTANCE: We have learnedin connection with Fig. 2 that currentis induced in a conductor when itcuts magnetic lines of force. Ifcurrent is caused to flow in a con-ductor a magnetic field is built uparound the conductor. As this fieldbuilds up, it cuts the same conductorwhich it encircles, and induces acounter electromotive force, resultingin a current in the opposite direction

Fig. 8. Hydraulic analogy illustrating thnaction of inductance.


in the conductor which opposes theoriginal current which produced themagnetic field. The overall effect ofthis is to cause the original cur-rent, as well as the magnetic field,to build up slowly, as though it wassluggish in action. The converse isalso true: if the original current isreduced or cut off entirely, the mag-netic field collapses and, in so doing,cuts the conductor once more, in-ducing a current in it which tendsto prevent the original current fromdiminishing. Thus, when an alternat-ing current (which is constantlychanging in value and direction) ispassed through a conductor it alwayslags in_ reaching its maximum andminimum values due to the counterelectromotive force and current whichit induces. It acts similar to mechan-ical inertia, and in electrical circuitsthis characteristic is called induc-tance. If the conductor is wrappedaround an iron core, a more power-ful magnetic field is produced andthe inductance is considerably in-creased. An inductance always im-pedes the flow of alternating current.Inductance is represented in a dia-gram by a coil.

The hydraulic analogy of Fig. 8represents inductance. Here a pad-dle wheel attached to a heavy fly-wheel is placed in the alternatingwater circuit. Remember that thewater is forced back and forth bythe reciprocating action of the piston.This tends to drive the fly -wheel firstin one direction and then in the other,but the wheel is heavy and cannotchange its direction of rotation rapid-ly. It always lags behind the pres-sure of the water.

CAPACITY: A condenser produces

9

Fig. 9. Hydraulic analogy illustrating theaction of a condenser.

just the opposite effect. This is rep-resented in the hydraulic analogyof Fig. 9. Here an elastic diaphragmis employed to represent the con-denser. It is evident that it com-pletely insulates one side of the watersupply from the other, but becauseit is elastic, it can stretch and allowthe water to flow back and forth.While the elastic diaphragm (con-denser) opposes the flow of water, itsprings back and tends to assist thecurrent of water to flow in the re-verse direction. Its action is fasterthan the piston action and it tends toforce the current of water throughthe circuit ahead of the pressure de-veloped by the piston.

The action of the condenser, there-fore, is opposite to that of the induc-tance. By combining the two in theproper proportion (a condition knownas resonance), one will exactly neu-tralize the other (for any given fre-quency) and the circuit will behave

10

as though it had neither inductancenor capacity and current will flowthrough the circuit in accordance withOhm's law. This is true for low fre-quency circuits only. For high or radiofrequency circuits in a state of reso-nance, the resistance is not equal tothe direct current resistance; thehigh frequency resistance of a wirebeing greater because the currentflows only on the surface; and alsoenergy is radiated in space, result-ing in a further loss.

POWER FACTOR: It is obviousthat in a circuit containing eitherinductance or capacity, there is al-ways an opposition (impedance) of-fered to the flow of alternating cur-rent, and this opposition is not theresult of the electrical resistance ofthe wires. Hence, it does not causeany heating. In measuring the power,or wattage of a circuit we have boththe true wattage absorbed by theresistance of the circuit, and thatwhich is momentarily absorbed by the

PRIMARY

IRON CORE

SECONDARY

Fig. 10. Simple transformer with two windings;primary and secondary.


inductance or capacity and is rede-livered to the circuit between im-pulses. This latter factor is calledthe wattless component. On this ac-count, the power (in watts) used inan alternating current circuit is notalways equal to the current times thevoltage, as in direct current cir-cuits. We have this wattless compo-nent to deal with, which is causedby either too much inductance or toomuch capacity. The circuit is nottuned to resonance. This wattlesscomponent is expressed in percentageand is called power factor. If thereis an alternating potential of 100volts and a current of one ampere andthe power factor is 80%, the actualor true wattage is equal to 100 x 1x .80 or 80 watts. In snaking alter-nating current measurements, remem-ber that the wattage consumed by adevice is seldom equal to the productof the current and the voltage. Alamp load is an example of a unit of(100%) power factor load. (Pureresistance load-no inductance orcapacity reactance.)

TransformersThe opposition offered to the flow

of alternating current by either aninductance or a capacity may be ex-pressed in ohms and is called im-pedance. In a transformer we havean iron core on which are placedvarious coils of wire. One coil, theprimary, is connected to the sourceof alternating current soppy; theother coil or coils are called second-aries and deliver current to othercircuits. Fig. 10 shows a simple trans-former having primary and second-ary coils and an iron core. When theprimary is connected to a source ofalternating current and the second-


ary circuit is open, it is obviousfrom the above explanation of in-ductance, that the primary coil offersconsiderable opposition to the flow ofcurrent, aside from that due to itsohmic resistance. Magnetic flux isstored in the iron core, and thisflux induces current in the primarycoil which opposes the original cur-rent which produced the flux. Theprimary is said to have high impe-d«nce, and little or no alternatingcurrent flows. The D.C. resistance ofthe primary winding may be so lowthat if, say, 100 volts D.C. were ap-plied to it, the coil would burn up.But if 100 volts A.C. were applied,there would be practically no cur-rent flowing due to the high A.C.impedance. The small amount thatdoes flow is just sufficient to make upfor slight losses in heating the wiredue to its ohmic resistance (I2Rlosses) and that which heats the ironcore due to the rapid changing of theflux, called hysteresis losses, or ironlosses.

When current is drawn from thesecondary coil, however, this cur-rent has the effect of opposing theflux producing it, thus weakening theflux in the iron core, and causingmore current to he drawn from theprimary circuit in order to bring theflux up to normal value to maintainequilibrium. Any current taken fromthe secondary is instantly reflectedon the primary. If ten watts arewithdrawn from the secondary, 10watts (plus losses) will he deliveredby the primary, and so on, up to themaximum rating of the transformer.If the transformer is rated at 100watts, and 150 watts are drawn fromthe secondary, it will get very hot.A 150 watt transformer would be

11

Fig. II. Schematic diagram of a radio powetransformer. Note the numerous secondary

windings.

identical to the 100 watt one exceptthat it would have larger wire whichwould carry the current and notget hot.

The voltage induced in a coil isProportional to the amount of mag-netic flux and the number of turns.It is evident from the foregoingthat if there be few primary turnswith a high voltage impressed uponthem, there must be much flux inorder that the back electromotiveforce impressed upon them willbalance out the applied electromo-tive force. This means that the ironcore must be large to carry the largeflux. Therefore, the size of a trans-former core depends upon the num-ber of primary turns. A small corerequires many turns and a large corefew turns. We can calculate thenumber of primary turns for any


given core size from the followingformula:

E X 100,000,000Tp

4.44 X f X a X Bwhere Tp - primary turns

E - primary voltagef - frequency in cycles per

seconda- cross-sectional area of

the .core in square inchesB - flu density in lines per

square inches, usuallyfor gOod transformercore steel . 60,000 linesper sqiiate inch

As an example, if We 'have a coremeasuring PA" by 1,/z" in cross sec-tion the area a would be 2.25 squareinches. The correct number of turnsfor a 110 -volt -60 cycle primary wouldbe

110 X 100,000,000Tp

4.44 X 60 X 2.25 X 60,000or 305 turns.

The size of wire to use dependsupon the wattage; a 200 watt trans-former should have a wire which willcarry twice as much current as a 100watt one.

The secondary turns may be cal-culated from the following formula:

sec. volts X pri. turnsSec. turns -

pri. volts.Any number of secondaries may

be wound on the one core, each onefor different current and voltageoutputs. Thus in Fig. 11 is showna radio power transformer withseveral secondaries. For a 250 watttransformer, using the core sizementioned above, the primary P

should have 305 turns. At 250 wattsthe primary current would he about(neglecting power factor) 21/4 am-peres. From our copper wire tablewe find that No. 14 wire is largeenough.

Secondary S1 may be wound for5 volts at 2 amperes. The samesize, (No. 14 wire) should be used.The number of turns should be

5 X 305Ts = or 14 turns.

110Secondary S2 may be wound for

700 volts, with a center tap, andfrom the same formula it shouldhave 1950 turns. For an output of150 miliamperes, No. 26 wire issufficient. In the same manner theturns and sizes of any number ofsecondaries, S3, S.t, S5 may be cal-culated. Always remember that thetotal wattage of the secondariesshould not exceed the wattage of theprimary. If it does, increase thesize of the primary wire to suit.

In a properly designed transformer,the secondary voltage should remainpractically constant regardless of theload placed upon it; that is, on loadsup to its maximum rated output.This is called regulation.

Wiring SystemsThe flexibility of alternating cur-

rent systems explains why it is ingeneral use throughout the countryin preference to direct current sys-tems. The losses in transmission ofelectric energy are the copper orPR losses. By reducing I (current)the losses are reduced and smallerwires may be used with a reductionin installation and transmission cost.By stepping up the voltage with atransformer, it is possible to reduce


INSULATOR

TO VARIOUSHOUSE

CIRCUITS

II

FUSES

SERVICEBOX

TO HOUSEFIXTURES AND

OUTLETS

SERVICEWIRE

METALCONDUIT

WATT-HOURMETER

SWITCH

FUSES

TRANSMISSIONWIRESITRANSFORMER rairSTEP-DOWN

.. . 1." "*".40.$.,-;"::;:;.::$.::::::11.1#

0;;,

BASEMENT

Fig. 12. Complete house wiring system. Note step-down transformer on pole.

the current, I considerably and stillhave the same amount of wattage orenergy. Thus the transmission of elec-tricity for house wiring usually takesplace over a 2300 volt circuit, a step-down transformer being placed out-side on a pole near the house forstepping down the voltage to 110.The 110 -volt secondary may supply

several residences, The current en-ters the residences usually in thebasement as shown in Fig. 12. Fromthere it passes through a fuse blockand switch to the watt-hour meterand from the meter to a distributingbox containing fuses for the varioushouse circuits. When a fuse blows,it generally happens in this box,


expansion is measured by a pointermoving over a scale. These metersare suitable for direct and alter-nating current measurements, bothlow and high (radio) frequencies.

Static meters are employed forvoltmeters and take no current atall but derive their action from therepulsion and attraction existing be-tween oppositely charged plates.

A wattmeter is an instrumentwhich measures both the voltage andthe current in a given circuit at thesame time, giving the result in watts,the unit of power. It consists pri-marily of two coils of wire, onemeasuring the voltage and the othercurrent, both acting on a single piv-oted pointer which moves across ascale, calibrated in watts.

A watt-hour meter adds anotherfactor-time-to the wattmeter. Thistime factor is introduced throughthe medium of a rotating disc gearedto a series of calibrated dials whichare read to determine the totalamount of watthours of electricityconsumed. The small metal disc is

Fig. 15. Illustrating the proper method ofconnecting the electric appliance cord to the

receptacle plug.

mounted on a pivot, in close proxim-ity to three coils through which thehouse current must flow before beingconsumed. As the current varies inthese coils the magnetic field in thedisc varies, producing eddy currentswhich cause the disc to rotate, thespeed of rotation depending upon thevalue of the current flowing throughthe coils. The current in one set ofcoils is proportional to the valueof voltage in the circuit. The othercoil, being in series with the line,measures the value of current in thecircuit. Hence the coils and the ro-tation of the disc, all working inunison, tell the story of the numberof watt-hours consumed.

Electrical AppliancesThere are various electrical ap-

pliances used in the average homethat sometimes need repairing, and theradio service man often has tinswork to do. He should know how toreplace broken cords in lamp sockets,etc. It is always best to open themain entrance switch in the basement(see Fig. 12) and thereby eliminateany possibility of short circuiting theline and blowing a fuse. In all pro-bability a fuse has blown, especiallyif a lamp cord or electric iron cordhas shorted and burned the wires intwo. Therefore, try lamps in socketsto see if the wiring is "alive." Oftenwires are pulled out of plugs. To fixthese, be sure to run the connectionsaround the plug contacts as shown inFig. 15.

To prevent wires from pullingthrough fixtures, the electrician'sknot, shown in Fig. 16, is employed.

Experiments Wit!, Alternating Current

This allows for considerable pullingon the cord and occupies little space.

There are all kinds of small mo-tors that occasionally need fixing.Vacuum cleaner motors, electric fans,radio phonograph motors, and manyothers become worn or refuse to run.If the motor is of the A.C. inductiontype, little can happen to it except aburned out coil or open circuit frommechanical injury. This must be test-ed and repaired if possible. In manycases universal motors are employed.These run on both direct and alter-nating current, and differ from in-duction motors mainly in that theyhave a commutator and brushes. Andhere is where almost all of the trou-ble begins. Both the brushes and com-mutator receive considerable wear.Sparking occurs and the commutatorsegments become pitted, making mat-ters worse. Remove the brushes andinspect them. Often they will befound to be completely worn out.Replace them with new ones. If thecommutator is badly damaged, themotor will have to be taken apart and

17

Fig. 16. The "Electrician's Knot."

the commutator turned down on alathe. By eliminating the sparkingof small household motors, much noisein the radio set will be eliminated.

Never oil the commutator. Oil isan insulator and will cause moresparking. A slight amount of gra-phite may be used in some cases.Motor bearings require occasionaloiling. These should be attended toregularly.

PART II

HOME EXPERIMENTS WITHALTERNATING CURRENT

Is It A.C. Or D.C.?UITE often it is necessary toascertain whether the currentin your home is either alternat-

ing or direct, that is, A.C. or D.C.One of the simplest experiments fordetermining this is to wave a pencil

or small stick back and forth betweenthe eye and an incandescent lampworking on that current. See Fig. 17.Assuming for the moment that thecurrent is of the common 60 -cyclealternating type, then, as you ap-proach its frequency (that is, as your

20

Fig. 20.First, it shows how a simple, workableA.C. electric horn can be made byplacing the bottom of a tin can nearthe laminated iron core of an A.C.electromagnet, and, secondly, it en-ables one to become familiar with a60 cycle tone, since the horn vibratesexactly 60 cycles per second (the fre-quency of the applied alternatingcurrent). In other words, it givesyou an audible picture of the alter-nating magnetic field in and aroundthe iron core and coil. It is goodpractice, in performing this experi-ment to connect a variable resistance,such as a 20 to 40 -ohm rheostat, orelse a good-sized 110 -volt incan-descent lamp, in series with the mag-net. This will prevent the possibleblowing of fuses or other "fireworks," should anything go wrong.Such a protective device is desirableeven if you happen to know that thecoil or magnet which you are goingto use has sufficient electrical resis-tance to prevent an undue flow ofcurrent.

Experiments With Alternating Current

The bottom of the tin can acts asa diaphragm, vibrating rapidly for-ward and backward at a rate of 60complete vibrations per second, thusproducing the noise which gives youyour horn.

A.C. Watch DemagnetizerVery often a watch, especially the

wrist or small pocket type, will keepexcellent time for many years, andthen for some apparently unknownreason will start to either gain orlose time. The reason might be thatthe iron parts in the movement mayhave become magnetized either throughassociation with radio or other elec-trical equipment, or from naturalcauses. This condition can very easilybe eliminated by de-magetizing thewatch as follows:

A coil of wire consisting of 20layers of No. 26 insulated magnetwire, such as double cotton coveredwire, is wound on a form of either

SLOTIF BRASSCORE IS

USED

WATCH

BRASS OR FIBREBOBBIN

LAMP OR RESISTANCE

COIL

Fig. 21.


brass, fibre or cardboard having aninside diameter of 21/2 inches anda length of 2 inches. See Fig. 21. Ifbrass is used, it should have a slotcut through the end rings and alsoalong the length of the tube to pre-vent eddy currents from being set upand cause the brass to heat up veryrapidly. The coil is connected in se-ries with a 100 -watt 110 -volt lamp,and the entire arrangement placedacross the 110 -volt A.C. line. Whenthe current is turned on, a very in-tense alternating magnetic field willbe produced in the center of the coil.If the watch is placed inside the coiland left there for but a few moments,it will be found that upon renewalit will once more give you excellentservice providing, of course, thatmagnetization was the cause of thetrouble in the first place. Such equip-ment has been made up by commer-cial firms and sold to the watchmak-ers' trade for this very purpose.

Simple A.C. Test ForMotor Armature Defects

Fig. 22 depicts a very practicalscheme for checking the continuityof coils on a motor armature. Mostarmatures have a great deal of in-dividual coils of wire wound on it,the ends of which are brought outto adjacent segments on the commu-tator ring. In commercial practice,expensive equipment is used to cheekthese coils. However, with a littleexperience this extremely simple andpractical method will do the trickvery nicely. A 110 -volt lamp with a40 -watt rating or more (dependingupon the size of the armature to be

21

Fig. 22.

tested, and the amount of the cur-rent required) is connected in serieswith two test wires, W, W which aretied on to the armature commutatorat two diamatically opposite segmentsby means of a piece of string. Thetips of a set of head phones or tele-phone receiver are then placed suc-cessively on two adjacent segmentsof the commutator. When the test-ing equipment is connected to the110 -volt A.C. line, a 60 -cycle toneor hum will be heard in the telephonereceiver. Once the operator becomesaccustomed to the volume of the tonefor a good coil, he will then be ableto determine by the difference orvariation in volume on succeedingtests whether the coil under test iseither shorted or open. A shortedcoil will result in a sharp attenuationor decrease in volume; complete ab-sence of the tone indicates that thecoil under test is shorted directlyat the commutator bars. If the in-

24 Experiments With Alternating Current

economical procedure inasmuch asconsiderable power has to be wastedthrough heat in the bank of lampswhich are generally used for thispurpose. It is mainly for this reasonthat charges were developed so thatstorage batteries can be rechargedthrough the use of alternating cur-rent. The procedure is to take thisalternating current, rectify it so asto produce direct current and. thenfeed this direct current to the bat-tery. "Rectification" consists of al-lowing the alternating current topass to the storage battery only atthat moment when it is surging for-ward and preventing it from passingto the battery when it is surgingbackards. To do this we must have adevice which would permit alternatingcurrent to pass only in one direction.This is the principle upon which alltypes of battery chargers, regardlessof how elaborate they are, operate.

Fig. 21A illustrates one of thesimplest (although not the most eco-nomical) forms of chemical rectifiers.Two plates, one made of lead and theother of aluminum, are immersed ina special solution of ammonium phos-phate known as an electrolyte. Abank of 110 -volt parallel lamps, orelse a suitable resistance such as acoil of iron wire, etc., is connected inseries with the storage battery andthe electrolytic solution. The actionof the electrolytic rectifier is suchthat it will permit current to pass inone direction only, from the lead plateto the aluminum plate. It will notallow current on the second half ofthe cycle to pass from the aluminumplate back to the lead plate. In this

manner the negative or reverse halfof a complete alternating currentcycle is "chopped off," so to speak,resulting in a direct pulsating cur-rent. This rectifier system is notthe most economical method forcharging a storage battery. A bet-ter method is illustrated in Fig. 21Bwhere a stepdown transformer isused instead of a bank of lamps ora resistance coil. The efficiency of atransformer is very high, being some-thing like 98%. The 110 volts of alter-nating current applied to the primaryis stepped down to approximately 8volts of A.C. in the secondary. Thislow voltage alternating current isthen passed through the electrolyticrectifier in the same manner as de-scribed above, thereby producing pul-sating D.C. This eliminates the lossof power due to the dissipation ofheat in the resistance coil or the elec-tric lamp bank.Simple A.C. Test For Condensers

A condenser consists of two metalplates separated by a non -conducivematerial. Condensers are used exten-sively in radio and electrical work,and frequently must be tested to seewhether or not they are defective.From the above description of a con-denser, it is easy to see that such aunit will not pass direct current inas-much as, essentially, it constitutes an"open" circuit. The plates merelybecome charged to the value of theapplied voltage and remain that way.A small momentary current doesflow in the circuit until the plates be-come fully charged at which point thecurrent ceases to flow.


In an A.C. circuit the picture isentirely different. Since the currentis constantly reversing its direction,the condenser in such a circuit willbe constantly charged and dischargedaccording to the frequency of thealternating current. Hence, while thecondenser is charging, a current willflow in the circuit in one directionand when it is discharging the cur-rent will flow in the other direction.Practically speaking, therefore, a con-denser does not hinder the flow ofalternating current. The amount ofalternating current which a condenserwill pass depends, of course, uponits size. This characteristic of acondenser to pass alternating current

us a means of testing themfor defects.

Fig. 25A clearly illustrates thesimple equipment necessary for per-forming such tests. It is merely nec-essary to have an ordinary 110 -voltlamp, (the power rating, in watts,depending upon the size of the con-denser to be tested) connected in se-ries with two test leads and the 110 -volt A.C. circuit. The test leads aretouched to the terminals of the con-denser under test. If the condenseris in good condition, the lamp willlight, but not to full brilliancy. Asthe capacity or size of the condenserbecomes smaller and smaller, you willnotice that the lamp lights up with di-minishing brilliancy. Once you haveestablished in your mind's eye, andwith the same bulb, the degree ofbrilliancy for a certain size condenser,you will then be able to readily de-termine whether the condensers undertest are normal or not. If the average

25

A. E.. HO VOLTS

LAMP110 V.-20-40 WATTS

LAMPBRIGHTEST

LAMPMEDIUM

A-

T -STEP DOWN TRANSFORMER

Fig. 25.

small condenser is tested in this fash-ion and the lamp lights up brightly,you can rest assured that the con-denser is broken down or "shorted."If a condenser is open, the lamp willnot light up at all. If the condenserbreaks down intermittently the lightwill flicker according to the frequen-cy at which the insulation in the con-denser is breaking down.

It is important to remember thatthe voltage rating of any condenserbeing tested by this method must beat least 100 volts. For condensershaving lower voltage ratings, it is

28

A.G. LINE

Fig. 29.

ALUMINUMRING

COIL

TACKS

the secondary winding of the secondtrasnformer, T2 as illustrated in Fig.28. The primary of the first trans-former represents the high tension orhigh voltage lines coming from adistant power house. The transformer,of course, represents the transformermounted on the transmission pole out-side the home. The secondary wind-ings represent the relatively low volt-age which finally enters the home andis used by the consumer. The sec-ond transformer proves to the experi-menter that the stepped -down volt-age can once more be stepped upeither to its original voltage or toany other desired voltage. The dia-gram in Fig. 28 illustrates this verynicely by showing a low -voltage lampbeing energized from the secondaryof the transformers and the higher -voltage lamp being energized from theprimary of the second transformer.Any number of different voltages canvery conveniently be produced


through the use of the proper trans-formers.

Magnetic LevitationThe levitated or floating ring ex-

periment, see Fig. 29 is a very in-triguing demonstration and has evenbeen used on the stage as a "trick ofmagic." Here an aluminum ringis placed on top of an A.C. electromagnet. When the magnet is ener-gized a rapidly alternating magneticfield surrounds the aluminum ring,causing an alternating current to beinduced in it. This induced currentalso produces an alternating magneticfield around the ring which in turnis reacted upon by the magnetic fieldof the A.C. magnet in such a man-ner as to cause the ring to fly awayor be "levitated" above the magnet.In order to prevent tile ring frombeing thrown entirely out of the mag-netic range of the magnet it is helddown by four threads tied in someconvenient manner. To the observertile ring apparently "floats in theair" with a gentle oscillating motion.This principle is the basis of the fa-mous levitated electric railway systemwhich has been proposed from time totime by many inventors. However, thepower required is so immense andthe efficiency so low, that it is doubt-ful whether such levitated train sys-tems can ever be devised for practic-al usage.

Frying Eggs On A Cake Of IceAnother "trick of magic" performed

on the stage is the frying of eggs ona cake of ice! See Fig. 30. This trick,however, is very simple and easily


explained in terms of electricity.When a solid piece of iron is placedin an alternating magnetic field, eddycurrents are produced in it whichtend to beat up the iron. Laminatedmetal, of course, is the remedy forthis condition as pointed out in pre-vious ,experiments. However, for thesake of this demonstration, we delib-erately use solid iron (or copper)since here we desire to create heatin the metal. The iron, in this in-stance, is a frying pan in which twoeggs arc contained. Underneath thefrying pan is placed a sheet of as-bestos and under that, the cake of ice.

As performed on the stage, theexperiment requires a large and verypowerful A.C. magnet. The A.C.magnet has a long laminated ironcore which reaches up into a holecut in the ice to within two or threeinches of the top of the ice. Whenthe current is applied to the magnetthe metal pan after a while becomesvery hot. The asbestos pad preventsthe heat produced in the metal panfrom melting the ice too rapidly. Themagnetizing coil generally comprisessix layers of No. 10 double cottoncovered magnet wire wound on aniron laminated core two inches squareand 15 inches long.

Simple A.C. MotorsEDDY CURRENT MOTO R.

Probably the simplest imaginableA.C. motor is the one illustrated inPig. 31 known as an eddy currentmotor. Here a metal disk made ofabout 1/32 inch copper or aluminum,is pivoted in such a manner as to befree to rotate in the field of an A.C.

ICE

ASBESTOSMAT

COIL

ASBESTOSMAT

EGGSFRYING/ IRON

PAN

TABLE

IRON PAN

TABLETOP

IRON CORE

TO 110 V..A.C. OUTL ET

Fig. 30.

clectro magnet. The principle ofoperation is quite simple. When theclear° magnet is energized an alter-nating magnetic field is produced inand around the laminated iron core.This rapidly changing field affectsthe metal disk in such a manner asto produce in it eddy currents whichin turn set up a magnetic field of itsown re -acting upon the original mag-netic field of the electro magnet.This interaction of the two mag-netic fields causes the disc to rotate.This is the same type of motor usedin the familiar watt-hour meter in-stalled in every home having clec-

30

LAMINATED IRON CORE

cCOPPERSHADING

RINGS

(DETAIL OF SHAFTAND BEARINGS

BEARING

BEARING by

COPPER DISC

SHAFT

DETAIL OFCOPPER SHADING

RINGS

Fig. 31. Simple Eddy Current Motor.

tricity. The power of the motor, aswell as its speed, can be improved byusing a copper shading ring in oneend of each pole of the electro-magnet. The method of attachingthese shading rings is illustrated inthe diagram. The direction of rota-tion of the disk depends upon whatend of the pole these shading ringsare placed.

SYNCHRONOUS MOTOR. Mostof the electric clocks have motorsof this type. These motors are verysimple and easily constructed. Fig.32 illustrates how this can be donefrom an old audio frequency trans -


former. A coil of wire having afairly high impedance (A.C. resis-tance) should be used. The statorand the rotor should be made oflaminated iron and should have anequal amount of notches cut intothem. The pitch, that is the widthand depth, of these notches, shouldall be alike. For experimental pur-poses these notches should numberabout six to ten (the illustrationshows ten in the stator). Synchro-nous motors do not start by them-selves; they must be started by hand.

Fig. 32. Construction of a synchronous motoras used in electric clocks. Note the laminated

iron core and toothed rotor.


SIMPLE INDUCTION MOTOR.Fig. 33 illustrates a simple A.C. in-duction motor, thousands of whichat one time were used for drivingelectric fans and similar equipment.Both rotor and stator are built upof laminated sheet iron to reduce

METALSHILL

SHADINGRING

ROTOR

COPPER.DISC

DETAIL OFROTOR -e

STATOECR POLEPIESFIELDCOILS

COPPER STRIPSCOPPER.

DISC

SHAFT

LAMINATEDIRON CORE

Fig. 33.

eddy current losses. The two polepieces on the stator arc wound withmagnetizing coils arranged in seriesand connected to the 110 -volt 60 -cycleA.C. line. The rotor is known as the"squirrel cage" type armature. About10 slots are cut in the rotor in alongitudinal plane. In these slots arcpressed strips of heavy copper wire.At both ends . of the armature theends of these wires are connected to-gether by means of copper rings, giv-ing the entire rotor the appearanceof a "squirrel cage." Copper shadingrings are wedged into the leadingedges of the stator pole pieces, theposition of these rings determine thedirection of rotation of the armature.

31

When the magnetizing coils areenergized, a rotating magnetic fieldis set up in the stator which causesthe rotor to rotate in the directiondetermined by the position of theshading rings. Induction motors arevery popular since they require nocommutators or brushes and henceare very quiet in operation. There isno sparking to cause radio inter-ference.

Lamp DimmerOne of the simplest methods of

dimming one or more lamps connectedto an A.C. circuit, is by means of aseries choke coil having an iron corewhich is easily slid in and out of thecoil. See Fig. 34. This coil may bemade of several layers of No. 14 orNo. 16 insulated magnet wire. Slidingthe core in and out of this coil variesthe A.C. impedance which the coiloffers to the alternating current. Asthe iron core is slid out of the coil,the impedance becomes less and hencethe voltage greater causing the lamp

Fig. 34.

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urrent

to become m

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core is pushed into the coil, the im-

pedance becomes greater, the voltage

applied lower, and the lam

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hichthe core is m

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equipment so that in the event of an

fr;

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depends upon the amount of current

to be used. Roughly, a 10 -w

att bulbw

ill pass 1/10th of an ampere; a 25 -

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No. 2-HOW TO MAKE THE MOST POP TLARALL -WAVE 1- and '2 -TUBE RECEIVERS

There has been a continuous demand right along for a low-priced book forthe radio experimenter, radio fan, radio Service Man. etc., who wishes tobuild 1- and 2 -tithe all -wave sets powerful enough to operate a loud -speaker.This book contains a number of excellent sets, some of which have appearedin past issues of RADIO -CRAFT. These sets are not toys but have been care-fully engineered. They are not experiments. To mention only a few of thesets the following will give you an Idea.The Megadyne 1 -Tube Pentode Loudspeaker Set. by Hugo Gernsback. Electri-fying the Megadyne. How To Tfalce a 1 -Tube Loud -Speaker Set, by W. P.Chesney, How To Make a Simple 1 -Tube All -Wave Electric Stt, by F. W.Harris. How To Build A Four -In -Two All -Wave Electric Set, by S. T.Barnsley, and others.

No. 4-ALL ABOUT AERIALSIn simple, understandable language this book explains the theory underlyingthe various types of aerials: the inverted "L." the Doublet. the DoubleDoublet, etc. It explains how noise -free reception can bo obtained, how low -impedance transmission lines work; why transposed lead-ins are use It gleesin detail the construction of aerials suitable for longwave broadcast receivers,for short-wave receivers, and for all -wave receivers. The book. Is written qisimple style. Various types of aerials for the amateur transmitting stationare explained, so you can understand them. It eliminates, once and for allthe confusion about the type of aerial to choose for best broadcast and short-wave reception. For the thousands of radio fans, both short-wave and broad-cast, who wish to know lust What type of antenna they should use and why,this book has been especially published.

BOOKS ARE ALL UNIFORM.Every book in the GERNSBACK'S EDUCATIONAL LIBRARY has 32pages-with illustrations varying from 30 to 66 in number. Each titlevolume contains over 15,000 words. POSITIVELY --THE GREATEST10c VALUE IN RADIO BOOKS EVER OFFERED TO THE PUBLIC.

Order hooks .by number-remit by check, money order, cashor unused U. S. Postage Stamps, Books are mailed POSTPAID.

RADIO PUBLICATIONS 101 HUDSON ST. Nrw YORK, N. Y.

for beginners - museum of yesterday...force that the friction heats the pipe to...

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