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(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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