(M^u^

- CIRCULATJOH

Cornell University Library

QC

645.H18its

The Tesla high frequency coH,

constr

3 1924

012 334 706

Cornell University Library

Thetine

original of

tliis

book

is in

Cornell University Library.

There are no known copyright

restrictions intext.

the United States on the use of the

http://www.archive.org/details/cu31924012334706

THE TESLA HIGH FREQUENCY COIL

Plate

1.

Complete

12" Apparatus.

Frontispiece.

THE TESLA HIGH FREQUENCY COILITS

CONSTRUCTION AND USESBY

GEORGE

F.

HALLER

AND

ELMER TILING CUNNINGHAM

S6

ILLUSTRATIONS

NEW YORKD.23

VAN NOSTRAND COMPANY191027

Murray and

Warren

Sts.

Copyright, 1910, by

D. Van Nosteand Company

X

The

Plimpioii Press

Norwood Mass. U.S.A.

INTRODUCTIONIn presentingthis

book on the Teslafilled

coil to thefelt

pubhc the

authors hope that they havepractical library of science.

a long

vacancy in the

No

attempt has been

made

to

give a mathematical explanation of the oscillation transformer,

and other parts of the high-frequency apparatus,simple reason that the theoryis

for the

too complex,

and when

obtained of no practical use.tried to lead thebellscell

Neither have the authorsis

amateur,

who

just learning

how

to string

and connect upto

batteries,

from the elements

of the galvanic

the working of a high-potential, alternating cur-

rent,

but have merely

made an

effort to place in the

hands of

advanced amateurs

in electrical science

a practical working

manual on

the construction of high-frequency coils,

now

so

useful in scientific investigation.

Thecoil

attention of the authors

was

first

called to the Tesla

when

they were fortunate enough to be given the use of

the 7" standard coil described in the last chapter of this

book.it,

A

systematic line of experiments was carried on with

in

order to study the effects of a change in the constantsAll the mechanical

of the various circuits.details of construction

andout,

electrical

were carefully worked

and

thecoil.

authors finally decided to design and construct a larger

The

coil,

as

first

constructed,

was a decided

failure,

due

to

VI

Introduction

too small a condenser capacity.further

For about

five

months they

experimented on the details of construction andbook.

finally arrived at the 12" coil described in thiscoil

ThisItis

they feel assuredto

is

as efficient

as can be made.

especially designed

give a

high-frequency discharge of

great volume.

This

latter fact

makes

it

useful for wireless

telegraphy.

In conclusion they have to thank Mr. G. O. Mitchell

for

manythis

suggestions

and

for the kindly interest he has taken in

work.

They

feel that

without his help the writing

of.

this

htde book would have been impossible.

G. F. H.E. T. C.

CONTENTSCHAPTERI.

PAGE

General Survey

.

i

II.

III.

IV.

V.

VI.VII,

The The The The The

TransformerCondenser

.

4. .

2024

Oscillation Transformer

Interrupter

.

.

.

32

Construction of the Boxes.

60.

Assembling

6472

VIII.

Theory of the CoilUses of the CoilDimensions of. .

.

IX.

.

.

84.

X.

7"

Standard Coil

Appendix

.......

97iii

LIST OF PLATESFACING

PLArEI.

PAGEComplete 12" ApparatusTransformer for 12" ApparatusOscillation Transformer and Glass for Condenser of 12' Coil

Frontispiece.

II.

20 20

III.I\'.\'.

.

Motor-driven Interrupter

..... . . . .

5252

The

Electrolytic Rectifier

VI.VII.

Discharge from the 12' Coil

96

The

7' Standard Apparatus

....

...

96

LIST OF FIGURESFIG.1. 2.

Method

of Fastening

Primary Terminals

Completed

PAGEPrimary8ii

Secondary Bobbin of Transformer

3. 4.5.

Hand WinderWire-spool Holder.

13

14

Frame

for Secondary of

Transformer.

18 18 2225

6.7. 8. 9.

Section of Completed Transformer

Condenser Frame and Brass Condenser Sheet End Support for Secondary of Oscillation TransformerFibre Strip

25

10.11.12.

Rod End SupportCentre

25for

Primary

28 29

13. 14.15. 16.

Primary of Oscillation Transformer . Completed Secondary of Oscillation Transformer Bushings for Support of Oscillator Standards.

29.

30 30 3437

Hard Rubber Block onSimple Primary Air-gap

Oscillation Transformer

17.18. 19.

Magnetic Interrupter

Motor Interrupter FanBrass Angle Piece

.

38 39 40

20.21.22.

Hard Rubber Block Section of the MotorPatterns of Base

Interrupter

.

41

42 44

23.24. 25. 26. 27. 28.

Patterns of

YokeMolor.

Section of Completed

45

Rotor Disc Rotor and Clamp NutStator Disc

46 48

49.

Frame

for Stator Coils.

51. .

29.

Self-starting DeviceRectifier Plates

52 5861

30. 31.32.

and

\\'iring

Diagram.

Transformer BoxHigh-tension

Box

63 65

33.

Connections for Primary of Transformer

xil

List of Figures

FIG.34. 35. 36. 37.

PAGEHigh-tension BushingOscillators

38.3940. 41.

and Standards Wiring Diagram Waves on Wires Primary and Core of Transformer Secondary Bobbin of Transformer Plate and Frame of Condenser.

...... -

^^7

0892

of 7' Coil of 7" Coil

98 99 loi.

Oscillation

Transformer of 7' ApparatusApparatus.

104 106107.

42. 43.

Box

for 7"

44.45.46.

Wiring Diagram Oscillators and Standards for 7' Apparatus

109113115

Transformer of Small Coil Completed Transformer of Small CoilOscillation

47. 48. 49.

Primary Spark-gap Wiring Diagram Wiring Diagram

.

.

117

.

118 118

.

THE TESLA COILCHAPTERI

GENERAL SURVEYByis

far the largest for

and most

interesting

branch of science

electricity,

Maxwell has proven mathematically, andlightis

Hertz verified experimentally, that

an ejectromagnetic

disturbance in the ether, and thus added that subject to the

realm ofelectricity,

electricity.

Amongst

the various

phenomena

of

those of the high-tension current are the most

interesting

and

instructive.

With such a current

all

the

wonders of the Geissler and Crookes tubes may be seen.

Withspace,

it

waves

for wireless

messages

may be

sent out into

and a great numberpurpose ofthis

of other experiments carried out.

It is the

book

to

show how a

satisfactory

apparatus for producing these currents

may

be constructed,

and

also to describe a few of the uses for such a coil.

Theknown

apparatus, as described in this book,

is

most commonly

as the Tesla High-Frequency Coil, and consists, in:

general, of four parts

i.

The Step-Up Transformer;4.

2.

The

Interrupter;

3.

The Condenser;

The

Oscillation Trans-

former.chapters.

Each

of these will be fully considered in subsequent

Before entering upon the description of the Tesla high-

frequency apparatus, however,

it

would be well

to

make a

few general remarks which are of the greatest importance.

2

The Tesla Coilof construction the

Throughout the whole working care

most

exact-

must be given

to the

matter of insulation.

All theinin-

wire used must be carefully tested, and each layer of wirethe transformer

must be thoroughly shellacked,

and then

sulated from the next layer, by two turns of carefully oiled

paper.

In the condenser, which

is

really the vital part of

the apparatus, the glass should be of the best grade obtainable.It

must

also be free

from

all

air bubbles.

It is in

the

high-frequency apparatus, howe^'er, that the greatest

care as regards both construction taken.

and

insulation

must

be

The

secondary consists of one layer only of No. 32

B.

& S.

gauge, double cotton-covered wire,

wound on

an

octagonal frame, formed of strips of vulcanized fibre fastenedto

two end pieces of wood.that

When When

winding the wire,

care

must be taken

no two adjacent wires touch,circuit.

for that

would cause a short wound,it is

the wire

is

completelyact

given about five coats of shellac, not only to

as an insulator, but also to prevent any slipping of the wires,

The primaryand asecondary.are

consists of a thin

band

of copper,

making

twothe

half turns

around a circular frame surroundingthe primary

The frames on which\'ery

and secondarj

wound must be

firm

and

sulDstantial, so that aithe

occasional jar will not displace any of the wires on

secondary.All

connections must be soldered,

and the

connecting

wires run through glass tubes.

When

the apparatus

is

finished,

two carefully made box6oil

must be constructed.

These must be

tight.

This

iii

General Survey

3

accomplished by mortisingboxes,shellac.

all joints,

and then givingfive

theof

especially

the joints,

about four orfits,

coatsinto

Into one box the transformer

and

the the

other the condenser

and

oscillation transformer.oil,

Thenis

boxes are

filled

with pure paraffine

which

the only

efficient insulator for these high-tension currents.

Some who

intend to build this coil will think that

all

these

precautions regarding insulation are extreme, but

it

will

be

found

that, in

dealing with high-frequency, high potentialcare cannot be taken, for

currents, toolationis

much

"Good

insu-

the key to success in high tension work."

CHAPTER

II

THE TRANSFORMER Thetransformer

sometimescoil that is

called

a

converter

is

merely an induction

connected directly to the

alternating-current mains, without the use of

an

interrupter,

andthethe

is

used to raise or lower the voltage.of watts

In a transformer

numbernumber

in the primary equals approximately

of watts in the secondary.

In the case of any step-up transformer, the ratio of the

numberondaryin the

of volts in the primary to those setis

up

in the sec-

nearly the

same as

thein

number

of turns of wire

primary to the number

the secondary;

but the

amperes decrease

in the inverse ratio.is

Theof

transformer used in the coil described in this book

the

common

induction-coil

type,

oil-immersed, step-up

transformer.at

It takes the alternating current

from the mainsvolts.

noThe

volts or 55 volts,efficient

and steps

it

up

to

about 10,000

working of a transformer depends largely

upon

the design of the core.

The

iron used

must be

of high straight

permeability and should havecoreits

little

retentivity.fall

A

is

always best to use;

for,

on the

of the current

fromits

maximum value to zero, the magnetic flux falls maximum value, not to zero, but to a value which

from

depends

The Transformeron the residual magnetism.opencircuit is

5

The

residual

magnetism

in

an

much

less

than in a closed magnetic

circuit,

so that

when

the current suddenly becomes zero, the

mag-

netic flux drops lower in

an open

circuit

than in a closed one.is

As

the electromotive force in the secondary

proportional

to the fall in the

magnetic

field, it is

greater with a straight

core than with a closed circuit of iron.

The

coil

designer

is

obliged to determine the length ofothers, as the

the iron core

from the experience ofit is

mathe-

matics for calculating

too complex, although simple

and

useful in the case of closed circuit transformers.is

If the core

made

too longif

the primary magnetizing current will be

too large, while

made

too short the secondary coilsto

would There

haveis,

to

be made of too large a diameter

be

efficient.

therefore, a certain length

which

will give the best results.

In the case of

this

transformer the length of the core wasall

determined after having gained

possible

information

from certain eminentmatters; in fact,this special useall

men who had madein this

a

life

study of these

the dimensions of the transformer for

were determinedis

way.

The

iron core

made up

of pieces of

No. 20 or 22 B.is

& S.

gauge iron wire 18" long.size

The

wire

first

cut nearly tothe ends of

with a pair of

pliers, and,'

when assembled,

the bundle are

sawed

off

square with a hack saw.little less

An

ordi-

nary piece of iron pipe, a

than 18" long, and havingis

an internal diameterwith these wires.

slightly less than 2",

tightly filled

When

putting the wires

in,

stand the pipe

on end on a smooth

surface,

and

force in each wire until

6it

The Tesla Coilhits this surface.is

When

the bundle

is

finished, the

upper

end

sawed

off -ith

a hack saw to exactly i8."is

Theor coal

tube containing the iron wiresfire

now

placed in a coke

and

left

there until the fire burns itself out, thus

insuring slow cooling.

This heating and subsequent slowis re-

cooling so softens the iron wires that their retentivity

duced

to

a minimum.

When

cool, the wires are

taken out

and sandpapered to ^emo^'e any superfluous oxide.then, one

They

are

by one, dipped into boiling water, wiped dry, and

while

still

warmis

are coated with thin shellac varnish.

When

the shellac

dry they are again packed, as tightly as possible,

in the pipe, to holdstill

them

in the desired shape.

Then, whileoutof

packed

closely together, they are forced slowly

the pipe; starting at the

end thus released, they are

tightly

bound with a narrow cotton bandage, which can be obtainedfrom any surgical supply house.

The bandage

should be

between one and two inches wide, but no more.entire coreis

When

the

wrapped with

this cloth, the cloth

should befiled flat

hea\ily shellacked.

The endsit is

of the core are

now

and smooth;oughly,

after thisit

put in a

warm

place to dry thor-

when

will

be ready for the primary winding.is

The

use of the insulating varnish on the iron wires

to arrestiron

eddy currents as much as possible, thus preventing the

wire from becoming heated and energy wasted, which would

lower the transformers

efficiently.

The primarycovered

is

wound

in

two sections of two layers each,&l S.

one above the other.copper wire

No. 12 B.is

gauge, double cottonwill

used.

About 2\ pounds

be

The Transformerrequired.

7

The primary may be wound by hand, by17"apart,

erecting2" hole

two wooden supportsbored in each,the core byasit it

and having a

to receive the iron core.

Then, by turningfairly well.

hand the wire may be wound

But

is

rather difScult to wind the wire tightly in this way,satisfactory toto one.

would be more

wind

it

in a lathe,it,

if

the

amateur has access

To mount

cut a half-inch

piece from the end of the pipe in which the core

was formed,

andring

slipfit

it

over the extreme end of the core.

Makeit

the

as tightly as possible

by placing between

and the

core a few strips of tin or other thin sheet-metal.it

Now clamp

firmly in the chuck.fitted

The

other end of the core should also

be

with a half-inch piece of pipe and supported at this

place in the steady rest.

The one

piece of pipe

is

used to

prevent any of the wires from being forced in unequally atthe points

where the chuck clamps

it,

and

the other to affordrest.

a smooth bearing surface for the steady

If there is

any tendency

for the core to slip out of the chuck, the tail

stock, with the centre

removed,

may

be pressed up against

it.

About

I ft.

from

the end of the copper wire take a coupleit.

of turns of tape

around

Atits

this point

bind the wire toseveral turnstightly

the iron core, about i" fromof tape

end,to

by taking

around

it.

Proceed

now

wind the wire

andof

closely to within i" of the other end.

Here the winding

the primary

is

stopped for a short time in order to give theAfter the shellac has dried,

wire a good coat of shellac.

another coating

is

given

it,

and thenwet.

the second layer

is

wound on

while the wire

is still

When

the winding

'

8

The Tcsla Coil

point, a has come to within about six turns of the starting

piece of tape doubled back

on

itself is laid

on the

first layer,

with

its

ends projecting beyond the

unwound

portion of thethe

second layer.

The looped end

of the tapei.

must be on

outer side of the winding.

See Fig.

/I

kf''')

Sji-ix^rams showing rnar^rter oC CasientTn^

la^t "tuTYt.

Fig

I.

Method

of Fastening Primary Terminals Primary.

Completed

The windingtape.

of the second layer

is

finished over the piecethe

of tape, the last turn being

brought through the loop in

The

loop

is

drawn

tight

by pulling on the otheris

pro-

jecting ends.off.

In

this

way

the last turn

kept from slipping

By

using this method or fastening

it is

unnecessary

to

use any bobbin heads for the primary;

this is

a decided

advantage,

as,

with a removable primary, bobbins are always

getting loose.

The

wire

is

cut off about

2'

from

this

ending

The Transformerin order

g

to allow

plenty of wire forwill

making the various

connections,

whichlayeris

be described in a later chapter.first

When

this

is

thoroughly shellacked, the

section

of the primary

complete.is

The secondstarting at thedirection.

section

wound

directly

on top of theto

first,

same end, and being surelayeris

wind

in the

same

Eachturn

when wound

is

thoroughly shellacked,as before.

and the

last

fastened in the

same manner

If the wire in the 16"

has been put on carefully 164 turns can be

wound

and the

totalis

diameter

will

be 2|".It will first

The secondary

wound

in four sections.

be

necessary to procure two micanite tubes,tightly within the other.

the one fitting

The

inner diameter of the smaller

tube

is

a

trifle

greater than 2!", the external diameter of the

larger

one being 35".-J".

The

length of the tubes

is

18"

and

their

thickness

Nowaround

turn out ait

wooden rod

so that the larger

tube will

fit

tightly.

Mount

the rod in the lathe

with the tube on

it,

clamping one end of the wood in the

chuck, and supporting the other end on a centre.thin parting tool, cut off seven rings, three i" wide,

With aandfour,

3^" wide.off in

If

the amateur has no lathe the rings may be cut

a mitre box.

Out

of

some quarter-inch

sheet-fibre,

cut eight circular pieces, 6" in diameterin the centre.

and having a 3" holeon the smaller tube,extreme end of the

Slip one of the 1" ringsit

and with Le Page's glue fastentube.

to the

Next

slip

on one

of the circular discs of fibre,

and

then one of the 3J" rings, fastening them with glue.

TwoAfter

more

discs are put on,

and then another 3^"

ring.

10this

Thecomes another3,{" ring.

I'rsld

Coilring, followed

disc

and a i"

by a disc

and a

Then put on two moreThisis

discs

and the remain-

ing 3 1" ring.ring.

followed by the remaining discis

and

i''

Be

sure that each ring

carefully glued

in

place.in

Before putting on the discs, small holes should be drilled

them, through which to carry the wires.

The The

romijlcteddiscs

bobbin for the secondarybereddrilled2,

is

seen in Fig.fcjr

2.

num-

3,

6,

7

ha\'e

the holes

the connecting wires

on\"

their inner edge, while the others their outer edge.

have them

drilled

about

from

Obtain a wooden rod uponlit

which the secondary bobbini8i" long.

will

tightly.

It

should be

If the coil builder is skilled in

winding wire

in the lathe,

the winding

may

be done there

much more

rapidly than bylittle

hand; but for an amateur,

who has had but

experiencelathe,

with lathe windirig, or for onethe following

who does

not possess ain

method

is

given.

In windingis

the lathe,

great care

must be takenis

that the wire

not snapped off whenis

the end

of the layer

reached, and while the jjaperis

being

wrapped on before the next layer

wound.

For the hand winder, the wooden rod, on which the secondary bobbinfits

tightly, is drilled in at

both ends for about

4" with a litde less than a {" hole.

Pieces of |" iron are thenaxh,-.

driven into these holes, to serve as anfit

They

should

tightly, so as to turn

with the cylinder.is

About 6" should1

project at one end,

which

bent into a handle.

!/'

at the

other end

is sufficient

for a bearing.

The

standards are

made

of

'("

oak, fastened jg|" apart,

The Transformer

II

^r-I*

9

-^

1-^

-Id-

Dimensions of

7"

Standard Coil

107

The condenser andin place,

oscillation transformer are

now putThesec-

the condenser being

between the two.

ondary terminals from the transformer are ledsuitably bent, directly to the condenser.the

in glass tubes,

From one

side of

condenser a wire

is

led to

an end of the primary band

on the oscillation transformer.

The remaining end

of the

copper band and the other side of the condenser are directly

connected to the two hinges of the cover carrying the interrupter.

All connections should be carefully soldered.

They

should be of about No. 20 B.in glass tubes

& S.

gauge copper wire, enclosedoil

and kept under the

as

much

as possible.

oo

Fig. 43.

Wiring

Diagram.

Any one of the forms of V can be used with the coil;

interrupters described in Chapter

the coil in question being equipped

with the motor interrupter.

The

connections between the

primary spark-gap and hinges can be run in glass tubes lyingin grooves cut in the

under side of the cover.

A

piece of

I"

hard rubber sheet should be screwed over the groovesis

wherever theretransformeror

any danger

of shorting to the core of the

primary terminals.diagram.

The

connections

are

shown

in the wiring

io8

TJic

Tcsla Coll

The

oscillators consist of

two brass

balls J" in

diameter

screwed on the end of twoto slide easily in

-^^" brass

rods 7" long, which are

two holes

drilled \"fibre

from the top of thethe rod.

standards, through both the

and

A

set

screw

at the top of each standard will be of convenience in clamping the rods in any desired position.

The standards

are constructed as follows.

Two

fibre or

hard rubber bushings 2" in diameter and iV'having a flange \" thick and 2^"in

in length

and

diameter turned on one

end are

set in

two holes cut in the cover directly abo^e the

holes in the brass bushings

on the

oscillation transformer.

A I" holediametertightly.

is

drilled

through the centre of each bushing.

Tworodsfibre

f " brass rods 8" long are enclosed in fibre tubes f " in outside

and

7 V'

long.

The

tubes

should

fit

the

The ends

of the brass rods project

from the

and should be

slightly

tapered to

fit

the bushings

on the

oscillation transformer.

In order that the discharge gapthe coilis

may

be adjusted while

in operation,

two

^'ulcanite

handles I" in diameter

are screwedfor

on the ends of the

rods, carrying the oscillators,

about

i\".

The

standards are

now

slid

through the bushings in the

cover until they

make good

contact with the bushings on

the oscillation transformer.

When

the coilit

is

now connectedbreak forthin

up

to the alternating current

mains,

will

a beautiful 7" discharge.If

everythingin the

is

not as

it

oughtin

to be, the trouble

may

be

found

manner described

Chapter VII.

-

Dimensions of 7" Standard Coil7

log

i f

m$$^^^\-

5

i

Oscillator **

%5tandar.i>

7 Coil

s"

hrasfi

rod

BUSHINQFiG, 44,

Foil

7 COIL7"

Oscillators

and Standards for

Apparatus.

APPENDIXForthose of our readers

who have

limited

means

at their

disposal,

and who

desire to carry

on some of the many experithis

ments possible with high-tension currents,has been added.

Appendixcities,

Besides

many

are not situated inis

where an alternating-current lighting supplybut

available,

who

possess an ordinary induction

coil,

giving a two or

three inch spark,

which they

may

substitute for the transarticle.

former to be described in the present

This

coil

isit

notis

oil

immersed, hence no boxes

will

be

required, as

simply mounted on a base in a place free

from dust and moisture.regarding insulation

A large

amount

of the precautions

and other things can be dispensed with,

thereby reducing the cost of the materials to within the reachof

almost every one.

While speaking of

cost, let

us state

that to purchase a coil giving a 12" spark from the regular

dealerscoil in

would mean an outlaya single boxis

of about

$300, while the 7"cost of construc-

worth S165.

The

tion

by the amateur, not considering

his time,

should not

exceed S50 for the 12" coil

and $25

for the 7" coil.3''

This piece of apparatus giving about anot exceed Sio to build at home.Itis

spark should

large

enough

for

most of the experiments on Roentgen and Geisler tubes andfor wireless

work

o\-er short distances.

112

The Tesla Coilincludethe

The above sums

simple

interrupter.

The

others will bring the price up in proportion.

The

high-frequency

coil is

made

as follows:

Cut out two

end pieces of i" wood lo" square and describe on each one two concentricrespectively.circles,

having diameters of 9 and

7

inches

On

these circles bore a

number

of \" holes i"mill

apart as in the figure.

Next procure from a planing

about twenty

Y dowels.

These are made of hard wood andinto 12" lengths

come 36"

long.

Cut each dowel

and

fit

one

in each of the holes on the smaller circle of one of the boards.

Whenempty

they are

all in

place the other board

is

put on theis

other end of the dowels.until the

Theis

outer circle of holes

left

secondary

wound.

TheB.

secondary winding consists of one layer of No. 32

& S.

gauge double cotton covered copper wire.

Begin the

winding about

Y

from the ends.

Shellac the wire with

several coats of the best orange shellacfinished.

when

the winding

is

The dowelsing

for the

primary are next put in place by pushIf theyfit

them through the holes from one end.

too

tightly the holes

may be reamedwound on

out.

Next

six turns of

No.

18 bare wire are

the outer dowels, each turn beingit.

over an inch from the one next to

The whole

coil is

then mounted on a base.

The ends

of

the primary are connected to two binding-posts

mounted on a

piece of hard rubber.

Two

oscillators

with standards are

provided for the terminals of the secondary.pletes the high-tension coil.

This com-

A ppendix

"3

^-

1

^--

114

'^^'^

Tesla Coil

The condenser

consists of fifteen sheets offoil

window

glass

lo" X 12", with a piece of tinof glass. follows:

8" x 10" between each sheetisit

The methodLay aWhile

of arranging this condenser

as a

glass plate

on a smooth

table

and

gi\e

coat of shellac.

still

wet place a sheet ofall

tin foil

onone

top of

it,

leaving an inch margin of glassfoil

around.

On

corner lay a strip of tinglass.

projecting an inch beyond the

On

top of this lay a second sheet of glass and anotherfoil,

sheet of tin

only the strip in this caseside.

is

brought out

on the opposite

Continue

this until the fifteen sheetsfoil,

of glass are used up.

This

will give seven sheets of tin

with the strips coming out on the one side and seven projecting

on the other

side.

The

strips

may

be fused together

with a hot iron and a copper wire soldered on.

The wholeandis

condenserbest

is

bound together within

insulating tape

mounted

a box.

This completes the condenser.1 00-110

The

transformer for use with theis

or 50-55 volt

alternating-current circuitsto construjt.Itis

the next piece of apparatus

essentially the

same as the two

trans-

formers already described.of

The

core consists of a bundle

No. 20-22 iron

wires, well annealed.after the

The

diameterin

is

lY and whenIIinis

formed

method described

Chapter

wrapped with

insulating tape.

The primarySee Fig.i

is

woundmethod

two sections one above the other.

for the

of fastening the layers.

Each

section consists of one layer of

No. 16 B.

& S.

gauge double cotton covered copper wire.is

After the primary

wound wrap onis

several layers of paperbuilt

well shellacked until the diameter

up

to 2}".

Appendix

"5

ii6

The Tesla CoilofS.

The secondary windingtwosections of

this

transformer consists of

No. 32 B.

&

gauge double cotton covered

copper wire.

First

saw out

of \" stock four circular pieces2 J" hole in the centre.

of wood, 4" in diameter

and having a

Slip these on the primary to the positions

shown

in the figure.

The two end

ones are |" from the ends of the core and the

middle ones are \" apart.

Windformedlayer

the wire of the secondaryuntil the

on the two spools Thoroughly

just

diameter

is

3J".

shellac eachnext.

and wrap a piececoil is

of paper

on before beginning the

The wholeIf the

mounted on a

suitable base, the primary

terminals being connected to binding-posts.

transformer

is

to

be operated on the loo-iio

volt in

current, theseries.If,

two sections of the primary are connectedit

on the other hand,

is

to

be u^ed on the 50-55Itis

volt current the sections are joined in parallel.

well,

however, in either case to bring the primary terminals outto

four separate binding-posts.

Theneither

the desired connecseries

tions

may

be readilycertain,

made

for

or parallel.

Always be

though, that the current will traverse

the windings in the

same

direction.

In order

to set

up the high

oscillations

we must

introduce

a spark-gap in series with the secondary of the transformer

and the high-tensionprimary spark-gapis

coil.

The method

of

making

this

given as follows: Procure two piecesDrill'

of vulcanized fibre rod |" in diameter 4 inches long.

a j" hole in each V' from one end.

Next bore two

-|"

holes

6" apart in the base of the transformer as

shown

in Fig. 47.

Appendix117

Drive the fibre supports into these holes with the holes in thefibre in line.

The spark-gapfibre

is

made

of

two }" brass rods 6" long with

tube

2''

long slipped over the end to act as an insu-

lating handle.

One

lead of the secondary of the transformer

goes directiy to one rod, the other goes to the primary of the

high-tension

coil.is

The

return wire from the primary of the

high-tension coil

soldered to the other side of the spark-gap.the condenseris

The diagram shows how

connected and also

the connections just described.

6

^H

^--

1-

--^

iFig. 47.

Prim-^ry Spakk-g.\p.

Therecare

is

no interrupter used withis

this

apparatus so that

must be taken that the spark

long enough to prevent

arcing.

Those possessing a suitable inductionto substitute this for

coil

and who wish

the transformer

and primarj' spark-gapDisconnect one

may do

so

by changing one connection.

terminal of the secondary from the dischargerthe

and connect

secondary terminal to a binding-post suitably insulated

by hard rubber.

One

terminal of the primary of the high-

ii8tension coilis

The Tesla Coilconnected to the spark-gap instead of the seccoil.

ondary of the inductiontension coils primary

The

other terminal of the high-

is

connected to the new binding-post.

A glance at the figure will make this plain and also the method

Fig. 48.*-^

WriUNG Diagram.

Fig. 49.

Wiring

Diagram.

of connecting

up the condenser.

When makingit is

connections

between the various parts of the apparatusthe wires in glass tubes

well to enclose

and

to

keep them back out of the way.is

The

operator will soon find that ordinary insulation

of

Appendixno value whateverin dealing

119

with these high-tension currents,

so that all terminals

must be kept apart a distance greaterIf this

than that of the high-tenson discharge gap.cautionis

pre-

not observed you will have some very beautifulall

brush dischargesclose proximity.

along the conductors that are in too

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