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2. energy
3. electricity

THE TESLA HIGH FREQUENCY COIL
Plate
1.
— Complete
12" Apparatus.
Frontispiece.
THE TESLA HIGH
FREQUENCY COIL
ITS
CONSTRUCTION AND USES
BY
GEORGE
F.
HALLER
AND
ELMER TILING CUNNINGHAM
S6
ILLUSTRATIONS
NEW YORK
D.
23
VAN NOSTRAND COMPANY
Murray and
1910
27
Warren
Sts.
INTRODUCTION
In presenting
this
book on the Tesla
authors hope that they have
filled
No
practical library of science.
pubhc the
coil to the
a long
felt
vacancy in the
made
attempt has been
to
give a mathematical explanation of the oscillation transformer,
and other parts of the high-frequency apparatus,
simple reason that the theory
is
obtained of no practical use.
tried to lead the
and connect
bells
cell
up
amateur,
batteries,
and when
Neither have the authors
is
just learning
from the elements
how
to string
of the galvanic
the working of a high-potential, alternating cur-
to
but have merely
rent,
who
too complex,
for the
advanced amateurs
manual on
made an
effort to place in the
in electrical science
hands of
a practical working
now
the construction of high-frequency coils,
so
useful in scientific investigation.
The
coil
attention of the authors
when
was
first
called to the Tesla
they were fortunate enough to be given the use of
the 7" standard coil described in the last chapter of this
book.
it,
in
A
systematic line of experiments was carried on with
order to study the effects of a change in the constants
of the various circuits.
details of construction
and
All the mechanical
were carefully worked
out,
electrical
and
authors finally decided to design and construct a larger
The
coil,
as
first
constructed,
was a decided
failure,
the
coil.
due
to
VI
Introduction
too small a condenser capacity.
further
For about
five
experimented on the details of construction and
finally arrived at the 12" coil described in this
coil
months they
they feel assured
especially designed
great volume.
is
to
This
as efficient
give a
latter fact
book.
as can be made.
This
It
is
high-frequency discharge of
makes
it
useful for wireless
telegraphy.
In conclusion they have to thank Mr. G. O. Mitchell
many
suggestions
They
and
for
for the kindly interest he has taken in
this
work.
this
htde book would have been impossible.
feel that
without his help the writing
G. F. H.
E. T. C.
of.
CONTENTS
CHAPTER
I.
II.
III.
IV.
V.
VI.
VII,
VIII.
IX.
X.
PAGE
General Survey
The
The
The
The
The
Transformer
4
.
Condenser
.
20
.
Oscillation Transformer
Interrupter
24
.
.
32
.
Construction of the Boxes
Assembling
.
.
7"
.
Standard Coil
64
72
.
Uses of the Coil
Dimensions of
60
.
.
Theory of the Coil
Appendix
i
.
84
.
.......
.
97
iii
LIST OF PLATES
FACING
PAGE
PLArE
I.
II.
III.
I\'.
\'.
VI.
VII.
Complete 12" Apparatus
Frontispiece
Transformer for 12" Apparatus
.
Oscillation Transformer and Glass for Condenser of 12' Coil
.
20
....
52
Motor-driven Interrupter
The
Electrolytic Rectifier
.
Discharge from the 12' Coil
The
7' Standard Apparatus
.
.
52
96
.
.
20
....
...
96
LIST OF FIGURES
FIG.
1.
Method
2.
Secondary Bobbin of Transformer
3.
Hand Winder
4.
Wire-spool Holder
Primary Terminals
of Fastening
— Completed
PAGE
Primary
8
ii
13
14
.
5.
Frame
6.
Section of Completed Transformer
for Secondary of
Transformer
18
18
.
22
8.
Condenser Frame and Brass Condenser Sheet
End Support for Secondary of Oscillation Transformer
9.
Fibre Strip
25
7.
10.
11.
12.
13.
14.
Rod
End Support
25
Centre
25
for
Primary
28
Primary of Oscillation Transformer .
Completed Secondary of Oscillation Transformer
Bushings for Support of Oscillator Standards
29
29
.
.
30
15.
Hard Rubber Block on
16.
Simple Primary Air-gap
34
17.
Magnetic Interrupter
37
18.
Motor Interrupter Fan
19.
Brass Angle Piece
20.
21.
Hard Rubber Block
Section of the Motor
22.
Patterns of Base
42
23.
Patterns of
Yoke
44
24.
Section of Completed
25.
Rotor Disc
26.
Rotor and Clamp Nut
48
27.
Stator Disc
49
Oscillation Transformer
38
.
39
40
Interrupter
41
.
Molor
45
-
28.
Frame
29.
Self-starting Device
30.
Rectifier Plates
31.
Transformer Box
for Stator Coils
and
30
\\'iring
46
51
.
.
.
.
.
Diagram
Box
32.
High-tension
33.
Connections for Primary of Transformer
52
58
61
.
63
65
List of Figures
xil
PAGE
FIG.
High-tension Bushing
35.
and Standards
Wiring Diagram
Waves on Wires
Primary and Core of Transformer
Secondary Bobbin of Transformer
Plate and Frame of Condenser
36.
37.
38.
3940.
Oscillators
92
of 7' Coil
98
of 7" Coil
99
loi
Oscillation
Transformer of 7' Apparatus
Box
Apparatus
43.
Wiring Diagram
Oscillators and Standards for 7' Apparatus
46.
47.
48.
49.
08
-
.
42.
44.
^7
.
41.
45.
^
.....
34.
for 7"
104
.
106
107
.
.
Transformer of Small Coil
Completed Transformer of Small Coil
Oscillation
Primary Spark-gap
Wiring Diagram
Wiring Diagram
115
.
.
.
109
113
.
117
118
118
THE TESLA COIL
CHAPTER
I
GENERAL SURVEY
By
is
and most
far the largest
electricity,
for
branch of science
interesting
Maxwell has proven mathematically, and
Hertz verified experimentally, that
light
is
an ejectromagnetic
disturbance in the ether, and thus added that subject to the
realm of
Amongst
electricity.
the various
phenomena
of
electricity,
those of the high-tension current are the most
interesting
and
With such a current
instructive.
all
the
wonders of the Geissler and Crookes tubes may be seen.
With
it
space,
waves
for wireless
and a great number
It is the
purpose of
this
messages
may be
of other experiments carried out.
book
to
show how a
apparatus for producing these currents
and
sent out into
may
satisfactory
be constructed,
also to describe a few of the uses for such a coil.
The
apparatus, as described in this book,
known
is
most commonly
as the Tesla High-Frequency Coil, and consists, in
general, of four parts
Interrupter;
former.
3.
Each
:
i.
The Step-Up Transformer;
The Condenser;
4.
The
2.
The
Oscillation Trans-
of these will be fully considered in subsequent
chapters.
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.
The Tesla Coil
2
Throughout the whole work
must be given
ing care
most
of construction the
matter of insulation.
to the
exact-
All the
wire used must be carefully tested, and each layer of wire
the transformer
must be thoroughly shellacked,
and then
in
in-
sulated from the next layer, by two turns of carefully oiled
In the condenser, which
paper.
really the vital part of
is
the apparatus, the glass should be of the best grade obtainable.
the
must
It
also be free
from
It is in
high-frequency apparatus, howe^'er, that the greatest
and
care as regards both construction
The
taken.
& S.
B.
air bubbles.
all
insulation
must
be
secondary consists of one layer only of No. 32
wound on
gauge, double cotton-covered wire,
an
octagonal frame, formed of strips of vulcanized fibre fastened
two end pieces of wood.
to
must be taken
that
would cause a short
wound,
When
winding the wire,
no two adjacent wires touch,
circuit.
When
the wire
is
care
for that
completely
given about five coats of shellac, not only to
it is
act
as an insulator, but also to prevent any slipping of the wires,
The primary
and a
half turns
secondary.
are
band
making
two
around a circular frame surrounding
the
consists of a thin
The frames on which
wound must be
\'ery
firm
of copper,
the primary
and
and secondarj
sulDstantial, so that ai
occasional jar will not displace any of the wires on
the
secondary.
All
connections must be soldered,
and the
connecting
wires run through glass tubes.
When
the apparatus
must be constructed.
is
finished,
two carefully made box6
These must be
oil
tight.
This
iii
General Survey
accomplished by mortising
boxes,
especially
shellac.
3
all joints,
the joints,
and then giving
about four or
Into one box the transformer
other the condenser
boxes are
filled
and
fits,
and
oscillation transformer.
with pure paraffine
oil,
coats
five
which
the
of
into
the
Then
the
the only
is
efficient insulator for these high-tension currents.
Some who
intend to build this coil will think that
precautions regarding insulation are extreme, but
found
that, in
currents, too
lation
is
all
it
these
will
be
dealing with high-frequency, high potential
much
care cannot be taken, for
"Good
the key to success in high tension work."
insu-
CHAPTER
II
THE TRANSFORMER
The
transformer
— sometimes
merely an induction
a
called
converter
is
the
number
the
number
an
interrupter,
In a transformer
used to raise or lower the voltage.
of watts
is
connected directly to the
coil that is
alternating-current mains, without the use of
and
—
in the primary equals approximately
of watts in the secondary.
In the case of any step-up transformer, the ratio of the
number
ondary
in the
of volts in the primary to those set
is
nearly the
amperes decrease
The
of
the
no
The
upon
common
induction-coil
type,
volts or 55 volts,
efficient
and steps
it
is
up
to
from the mains
about 10,000
volts.
working of a transformer depends largely
The
always best to use;
for,
iron used
little
on the
must be
retentivity.
fall
A
of high
straight
of the current
maximum value to zero, the magnetic flux falls
maximum value, not to zero, but to a value which
its
but the
oil-immersed, step-up
It takes the alternating current
the design of the core.
is
of turns of wire
the secondary;
in
in the inverse ratio.
permeability and should have
core
number
the
in the sec-
transformer used in the coil described in this book
transformer.
at
same as
primary to the number
up
from
from
its
depends
The Transformer
The
on the residual magnetism.
open
much
circuit is
when
so that
magnetism
residual
than in a closed magnetic
less
in
an open
circuit
mag-
than in a closed one.
the electromotive force in the secondary
magnetic
to the fall in the
field, it is
an
circuit,
the current suddenly becomes zero, the
netic flux drops lower in
As
5
proportional
is
greater with a straight
core than with a closed circuit of iron.
The
coil
designer
the iron core
is
obliged to determine the length of
from the experience of
matics for calculating
it is
others, as the
too complex, although simple
useful in the case of closed circuit transformers.
is
made
have
is,
to
made
if
If the core
too short the secondary coils
be made of too large a diameter
therefore, a certain length
In the case of
and
the primary magnetizing current will be
too long
too large, while
mathe-
which
to
be
efficient.
would
There
will give the best results.
transformer the length of the core was
this
determined after having gained
all
information
possible
from certain eminent
men who had made
matters; in fact,
the dimensions of the transformer for
were determined
this special use
The
all
iron core
is
made up
gauge iron wire 18" long.
size
with a pair of
the bundle are
off
nary piece of iron pipe, a
an internal diameter
with these wires.
The
pliers, and,'
sawed
wire
study of these
life
way.
No. 20 or 22 B.
is
when assembled,
the ends of
square with a hack saw.
little less
An
ordi-
than 18" long, and having
putting the wires
surface,
& S.
cut nearly to
first
slightly less than 2",
When
on end on a smooth
in this
of pieces of
a
and
is
in,
tightly filled
stand the pipe
force in each wire until
The Tesla Coil
6
it
When
hits this surface.
end
is
The
sawed
off «-ith
the bundle
fire
and
left
upper
finished, the
a hack saw to exactly i8."
tube containing the iron wires
or coal
is
is
now
placed in a coke
there until the fire burns itself out, thus
This heating and subsequent slow
insuring slow cooling.
cooling so softens the iron wires that their retentivity
duced
to
When
a minimum.
cool, the wires are
is re-
taken out
They
and sandpapered to ^emo^'e any superfluous oxide.
are
then, one
by one, dipped into boiling water, wiped dry, and
while
warm
still
the shellac
is
dry they are again packed, as tightly as possible,
in the pipe, to hold
still
packed
When
are coated with thin shellac varnish.
them
Then, while
in the desired shape.
out
closely together, they are forced slowly
the pipe; starting at the
end thus released, they are
of
tightly
bound with a narrow cotton bandage, which can be obtained
The bandage
from any surgical supply house.
should be
When
between one and two inches wide, but no more.
entire core
is
wrapped with
The ends
hea\ily shellacked.
and smooth;
oughly,
when
after this
it
will
this cloth, the cloth
it is
of the core are
put in a
warm
the
should be
now
filed flat
place to dry thor-
be ready for the primary winding.
use of the insulating varnish on the iron wires
is
The
to arrest
eddy currents as much as possible, thus preventing the
iron
wire from becoming heated and energy wasted, which would
lower the transformers
The primary
is
efficiently.
wound
in
two sections of two layers each,
one above the other.
No. 12 B.
covered
is
copper wire
used.
&l S.
gauge, double cotton-
About 2\ pounds
will
be
The Transformer
The primary may be wound by hand, by
required.
two wooden supports
bored in each,
it
is
and having a
apart,
But
fairly well.
satisfactory to
wind
To mount
to one.
in a lathe,
it
it,
and
slip
ring
fit
was formed,
Make
over the extreme end of the core.
it
as tightly as possible
by placing between
fitted
The
it
the
and the
Now clamp
core a few strips of tin or other thin sheet-metal.
firmly in the chuck.
the
if
cut a half-inch
piece from the end of the pipe in which the core
be
2" hole
rather difScult to wind the wire tightly in this way,
amateur has access
it
erecting
Then, by turning
to receive the iron core.
would be more
it
17"
hand the wire may be wound
the core by
as
7
other end of the core should also
with a half-inch piece of pipe and supported at this
The one
place in the steady rest.
piece of pipe
is
used to
prevent any of the wires from being forced in unequally at
the points
where the chuck clamps
and
it,
the other to afford
a smooth bearing surface for the steady
any tendency
stock, with the centre
About
I ft.
from
of turns of tape
removed,
around
At
it.
Proceed
it.
may
be pressed up against
this point
end,
its
now
to
is
several turns
wind the wire
tightly
and
Here the winding
of
stopped for a short time in order to give the
wire a good coat of shellac.
another coating
wound on
bind the wire to
by taking
closely to within i" of the other end.
the primary
it.
the end of the copper wire take a couple
around
the iron core, about i" from
of tape
If there is
rest.
for the core to slip out of the chuck, the tail
is
given
while the wire
it,
After the shellac has dried,
and then
is still
wet.
the second layer
When
is
the winding
'
The Tcsla Coil
8
point, a
has come to within about six turns of the starting
on
piece of tape doubled back
with
its
ends projecting beyond the
The looped end
second layer.
unwound
of the tape
See Fig.
outer side of the winding.
— Method
The winding
The
of the second layer
loop
jecting ends.
off.
By
In
is
drawn
this
way
is
as,
Completed
finished over the piece
brought through the loop in
tight
by pulling on the other
the last turn
is
using this method or fastening
getting loose.
the
la^t "tuTYt.
the
pro-
kept from slipping
it is
use any bobbin heads for the primary;
advantage,
must be on
of Fastening Primary Terminals Primary.
of tape, the last turn being
tape.
portion of the
kf''')
Sji-ix^rams showing rnar^rter oC CasientTn^
I.
first layer,
i.
/I
Fig
on the
itself is laid
unnecessary
this is
to
a decided
with a removable primary, bobbins are always
The
wire
is
cut off about
2'
from
this
ending
in order
to allow
layer
this
of the primary
The second
and the
be described in a later chapter.
will
thoroughly shellacked, the
section
is
wound
directly
when wound
layer
fastened in the
is
is
on top of the
to
wind
diameter
total
wound
is
a
is
larger
as before.
trifle
in four sections.
The
thickness
-J".
tube will
fit
It will first
Now
The
the one fitting
inner diameter of the smaller
length of the tubes
turn out a
around
with the tube on
it,
it
wooden rod
Mount
tightly.
is
18"
and
the rod in the lathe
clamping one end of the wood in the
thin parting tool, cut off seven rings, three i" wide,
If
their
so that the larger
With a
chuck, and supporting the other end on a centre.
off in
be
greater than 2!", the external diameter of the
one being 35".
3^" wide.
wound
be 2|".
necessary to procure two micanite tubes,
tightly within the other.
same
in the
same manner
will
first,
thoroughly shellacked,
has been put on carefully 164 turns can be
and the
The secondary
tube
section
first
complete.
turn
last
in the 16"
making the various
is
is
Each
If the wire
plenty of wire for
same end, and being sure
starting at the
direction.
g
which
connections,
When
The Transformer
and
four,
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 diameter
and having a 3" hole
Slip one of the 1" rings
on the smaller tube,
in the centre.
and with Le Page's glue fasten
tube.
Next
slip
on one
it
to the
extreme end of the
of the circular discs of fibre,
and
then one of the 3J" rings, fastening them with glue.
Two
more
After
discs are put on,
and then another 3^"
ring.
The
10
this
comes another
and a
Be
ring.
and a i"
disc
This
is
by a disc
ring, followed
Then put on two more
3,{" ring.
ing 3 1" ring.
Coil
I'rsld
discs
and the remain-
and
followed by the remaining disc
sure that each ring
carefully glued
is
Before putting on the discs, small holes should be drilled
them, through which to carry the wires.
The
bobbin for the secondary
The
bered
2,
drilled
on
about
\"
3,
7
6,
seen in Fig.
is
the holes
ha\'e
2.
romijlcted
discs
num-
have them
drilled
Obtain a wooden rod upon
their outer edge.
which the secondary bobbin
in
the connecting wires
fcjr
their inner edge, while the others
from
i''
place.
in
will
lit
tightly.
It
should be
i8i" long.
winding wire
If the coil builder is skilled in
the winding
may
be done there
hand; but for an amateur,
who has had but
with lathe windirig, or for one
the following
great care
the end
method
is
must be taken
of the layer
is
much more
who does
rapidly than by
little
that the wire
is
experience
not possess a
In winding
given.
in the lathe,
in
the lathe,
not snapped off when
reached, and while the jjaper
wrapped on before the next layer
is
lathe,
is
being
wound.
For the hand winder, the wooden rod, on which the secondary bobbin
fits
tightly, is drilled in at
4" with a litde less than a {" hole.
driven into these holes, to serve as an
fit
tightly, so as to turn
project at one end,
other end
The
standards are
axh,-.
with the cylinder.
which
is sufficient
both ends for about
Pieces of |" iron are then
is
They
should
About 6" should
bent into a handle.
1
!/'
at the
for a bearing.
made
of
'("
oak, fastened jg|" apart,
The Transformer
^
„9
II
-^
1-^
r
-I*
-Id-
<5^
f
^
-I*
"1
^
4e-
:,f^i^,^^-J^.?/-^
long
is
oak f" square and 2"
piece of
fastened with two screws to the top of each standard,
to serve as a cap.
on the
its
A
2' long.
a baseboard
to
Tesla Coil
Tlie
12
I" hole
then bored with
is
This allows the cylinder
joint.
bearings
A
when
Two
necessary.
its
centre
be taken out of
to
iron washers are slipped
over the shaft at the short end to act as a thrust bearing,
and two washers, with an open,
steel-wire spring
them, are put on the other end.
This
between
will give the friction
required to enable the amateur to stop the winding at any
time,
and
still
be sure that the cylinder will not rotate and so
The dimensions
loosen the turns of wire.
seen in Fig.
As
it is
of the winder are
3.
the wire
must be wound under some
tension,
and
as
tiresome to give the required tension by letting the wire
run through the hand, the holder shown in Fig. 4 was
devised.
It consists of
is
an axle which
fits
4" longer than the spool.
There
end of this axle for about 2"
wooden standards fastened
are put between the spool
to
bear on.
up on
A
An
the spool tightly,
to a
is
and which
a thread cut on one
then mounted in two
It is
baseboard.
and the standards
Iron washers
for the spool
open spring made of piano wire
is
slipped
the threaded end of the shaft, outside of the standards.
washer and a nut are now put on
A
tension to the spring.
lock nut
is
to give the required
put on to keep
this
nut from turning.
Care must be taken
in the wire.
When
to detect
any breaks that may occur
winding the wire
it
quite frequently
The Transformer
13
c
o
"n
-a
I
M
F\
O
C5
The Tesla Coil
14
happens that a
it is
covered by
bobbin,
little
kink
cause a break; but because
will
the cotton insulation,
unknown
it
will
To
to the coil builder.
be
wound on
detect these breaks
immediately, the authors used the following method.
is
cut out of a piece of sheet brass or copper.
and
3" in diameter.
This
is
the
It is
A
ring
}" wide
fastened by several flat-headed
brass screws to one side of the spool on which the wire
is
/
^
8
Fig. 4.
bought.
If the
— \\'ire-Spool
Holder.
wire has been bought from a reliable dealer,
the inner end will be found projecting outside of
This wire
A
is
strip of sheet
that
it will
is
copper or brass, which
bear on the ring,
the standard,
a wire
the
reel.
soldered to the ring on the outside of the spool.
is
is
of such a length
fastened to the upper end
on the side on which the ring
led to
one pole of a dry
cell.
is.
From
of
here
The Transformer
On
15
the winder a strip of sheet metal
the standards.
is
best to fasten
It
is
It
from the handle.
it
bent so that
is
fastened to one of
to the
make good
projecting axle, which has been polished to
A
trical contact.
wire
one farthest up
presses firmly on the
it
then led from the brush on the
is
standard to a binding post on the baseboard.
receiver
now connected
is
the other pole of the
head attachment,
is
the Bell receiver,
easily
elec-
in series
A
cell.
A
telephone
with the binding-post and
watch-case receiver, with a
the best to use.
an attachment
If the
to hold
amateur has only
to his
it
head can
be arranged.
If the
amateur
may
prefers he
use a sensitive
galva-
nometer.
Everything
To
is
now ready
begin, pass about
i'
bobbin heads numbered
head 2
is.
The
wrapped on
wooden
circuit
cylinder.
through
2, 3,
from the side on which bobbin
all
and then
this
It will
now be
the wire
seen that there
on the
used, the needle will be deflected.
will
its
is
and the
a complete
The diaphragm
spool.
drawn down or
break, the diaphragm will return to
a click
bare part should be
the axle between the washer
in the telephone receiver is
is
winding of the secondary.
insulation should be scraped off of the end
of the wire for about 2",
tightly
for the
of the wire through the hole in the
if
If
a galvanometer
the wire should
normal position and
be heard, or in the case of the galvanometer the
needle will return to the zero position.
the break should be located
and
When
the wire
should not be used in soldering, as a
this
happens
soldered.
little left
Acid
on the wire
6
The Tesla Coil
1
will corrode
is
and
it
the best thing to use as a flux.
The
layer in the section between the bobbin heads
first
wound from
I, 2, is
2 to
i,
and
a good coating of shellac.
a
Rosin
connection.
spoil the electrical
The edge
is
wax must not be used
when
sulation, as the transformer
paraffine
oil,
thus spoling
the
first
its
layer,
down with a
little
to increase the in-
finished
immersed
is
in
All the layers after
insulating properties.
should start about \" from the inner face of the discs
each layer after
The
given
it is
which acts as a partial solvent to paraffine wax,
and stop the same distance from them.
around
wound
taken around the pre\ious
of the paper can be held
Parafiine
shellac.
it is
Before winding the next
over a turn of paper
little
one.
after
it.
it
is
wound and then
Be sure
to shellac
take a turn of paper
Continue winding until 61 layers are
last layer
in place.
should be wrapped over with a narrow cotton
bandage which
is
thoroughly shellacked to keep
About two
feet of wire
section for
making the various connections.
then brought through
should be
it
in place
projecting from the
left
the hole in disc
i,
This wire
and
its
end
is
is
connected to the axle.
Unwind
the other wire from the axle and, after polishing
the uninsulated part with a piece of
emery
cloth, t^vist
around the end of the wire from the spool, which has
been polished, and then solder the connection.
bare part of the wire with some
insulate
The
it
also
\\'rap the
silk thread, so as to thorou'^hly
it.
section
between the bobbin heads
3, 4, is
now wound.
The Transformer
The
;
layer
first
is
wound from
17
towards
j
the winder being
4,
turned in such a direction that the direction of the current
in the wire of this section will
That means
wound.
the
opposite
be the same as in the one just
must be rotated
that the winder
direction.
For convenience, howe\er,
winding the secondary bobbin can be taken
rod and put back in a reversed position,
the winder
rotated the
is
same
the
wooden
off of the
^^hen
in
in
this
is
done
The same
as predously.
instructions hold for this section as for the pre\"iou5 one.
Each
layer
must be shellacked and wrapped with paper and
the winding
In
must stop before getting
this section
71 layers are
wound
bobbin heads.
to the
on.
About
2'
of wire
should be brought through the hole in disc 4 to allow for
;
connections.
The two remaining
-
now wound
sections are
in the
manner, there being 71 layers in the section between the
bobbin heads
the discs
the
5, 6,
Remember
7, 8.
same
and only 61
to
la\ers in the section
This method of winding
as in the previous coils.
A
static strains.
practical reason
that
is
wires are from the outer layers, thus
to bring
out a
The reason
middle
.
new
piece of wire
and
if
for ha^'ing a greater
coils w-ill readily
direction
between
keep the direction of the wire
has several advantages, one of them being that
;
same
relieves
the leading out
all
making
it
an}- are ever
number
it
ahvavs easy
broken
off.
of la}-ers in the
be seen from a consideration of the
intensity of the lines of
magnetic force around
a solenoid.
Leave the completed secondary
in
a
warm
place to thor-
The Tesla Coil
^'V
<t'V----7f"
Fig.
5.
— Frame
7i
ff
for Secondary of Transformer.
oughly dry, and in the meantime construct the frame
secondary.
base
is
made
Working drawings are given
in Fig.
of a piece of i"x 9" pine 20^" long.
and edges are rounded
to give
it
5.
The
a better apgearance.
for the
The
comers
Three
supports of i"x7" pine, 4V' high, are erected at the points
m.
1!
Fig. 6.
,.r,r..—.nm-rrrr-g^
— Section
!lbi'Anm(Trn-F-n-3T^"'T:::r;
of Completed Transformer.
The Transformer
shown
in the figure.
3j" in diameter
the secondary
is
is
is
At the top
of each a half-round hole
Into these
cut.
wound.
The
19
fits
the tube
on which
distance between the supports
7r.
The two
are
silk
now
terminals from the middle coils of the secondary
soldered together, and the connection wrapped with
thread to insulate
it.
The
other two terminals are
left
alone at present as their connections are described in a later
chapter.
The
reason for using a cotton cloth instead of tape in the
construction of the transformer
is
that
oil
almost immedi-
ately spoils all the adhesive qualities of the type.
CHAPTER
III
THE CONDENSER
A
CONDENSER
is
an apparatus
for accumulating a large
quantity of electricity on a small surface.
vary considerably, but in
all
cases
The form may
consists essentially of
it
two conductors separated by a non-conductor or
and
its
The
action depends entirely
upon
induction.
thinner
and
the
the
dielectric
inductive capacity, the greater
A
denser.
potential.
is
greater
dielectric,
its
specific
the capacity of the con-
thin dielectric, however, cannot withstand a high
Besides the thickness, the dielectric strength
de-
pends on the character of the material.
The condenser used
for
in this
apparatus
used
is
glass
and the
plates are
finished the condenser
For the
in size,
is
made
immersed
especially designed
in
yV thick and
When
oil.
io"xi2"
These sheets may be had
them each sheet should be examined
If
dielectric
pure parafi&ne
about nine or ten cents apiece.
are any air bulAles.
The
of sheet brass.
dielectric 95 sheets of glass,
should be obtained.
to size for
it
is
long continued use on high voltages.
carefully to see
any are found
in
cut
In purchasing
if
there
a sheet of
glass
should be rejected.
The
brass used
is
number 32
or 34.
Forty-six sheets
Plate
Plate
III.
—
II.
— Transformer
for 12" Apparatus.
Oscillation Transformer
12" Coil.
and Glass
for
Condenser of
The Condenser
8"xio" are required.
side
In one of the corners of the shorter
a tongue 2" wide and
is
the top of this tongue.
wide, a
out of
little
soldering
As a
right
on the
is
this
the tongues cut
The
extra i"
is
Rosin, not acid, should be used
in the
width
is
used the tongues are cut
occupies the part that has been constructed
which the condenser
is
pine.
The
base
long.
The
sides are
is
The frame
transformer box.
built
made
up
is
made
in
out of well dried
of a piece of ]" x 11" pine, iif"
cutout of y'xi2" material lof"
are also cut from j"xi2"
wood and
long.
are 11" long.
and ends should be planed up smooth on both
sides, so as to
make them
completed frame
is
a
little less
seen in Fig.
The
than i" thick.
7.
Place the condenser frame on a table or some other
surface, with
one of the ends down.
clean so as to
remove any dust or moisture.
by putting two glass sheets
bottom of the frame.
glass plates so that there
sheet, except
in the
flat
Before putting any of
the glass sheets in the frame, they should be carefully
the
for
sheets.
in the oscillation
sides
rolls 8"
the only width that can be obtained in
When
The condenser
The
bent across
in the figure.
rule 12"
The ends
is
can be had in
cut 3"xi|".
to the plates.
shown
places.
it
If the brass
hp
These tongues should always be soldered
most
for
A j"
j" long.
more should be obtained and
them
as a flux.
position
i
They should be
it.
21
wiped
Commence
frame so that they reach
Place a brass sheet on top of these
is
a i" margin of glass
were the tongue comes out.
If
all
around the
the lip
on the
The Tesla Coil
22
tongue has been bent carefully
will just
fit
up against
Without displacing the brass lay two
sheets of glass.
on top of
of glass
it
it.
A brass
sheet
next put
is
i"
margin around the brass as in the previous
the brass
come two more
but in
this
There should
case the tongue comes out on the reverse side.
be a
in,
the
sheets
case.
After
This process
sheets of glass.
is
A.
n." "Frame for
B."Sha|3=
Dotted
tort4ue
Fig,
7.
— Condenser
Condenser
brass jheet
show size op
o^
lines
w^dn so\<ierG6 on.
Frame and Brass Coxdexser Sheet.
kept up until the 46 sheets of brass have been put in
Three sheets
If the glass
book
last
of glass are placed
the last sheet will just go
few sheets
two, to take
on top of the
and the brass used are the
it is
last brass plate.
size called for in this
In forcing in
the
a good idea to lay a cloth between the
last
up any excess
crack the glass.
m
place.
tightly.
pressure,
which would otherwise
The Condenser
Set the condenser upright,
when
23
finished,
No. 16 bare copper wire about
piece of
down
the lips in turn,
the one side,
and
3'
the
and
solder a
long to each of
same
is
done on
the other side.
Two
frame
leather straps should be fastened to the sides of the
to
lift
former box.
it
by when lowering
The
into the oscillation trans-
object for building the condenser in a
separate frame, instead of in the division in the oscillation
transformer box,
ever require
shet
is
to facilitate
rebuilding,
due
moving should the condenser
to
the rupturing of the glass
.
AA'hen the condenser
is
placed in the box, the end which
has the three glass sheets should be placed against the partition, that
is,
nearest the oscillation transformer.
pre\-ent the spark
from the
This
oscillation transformer
through into the condenser, instead of following
its
is
to
breaking
air path.
CHAPTER
I\'
THE OSCILLATION TRANSFORMER
It
in
is
this part of the
apparatus, so simple in construction,
which the most care as regards insulation must be taken.
The
success of the whole apparatus depends on the care
with which this part
is
The
constructed.
as two wires touching, or
many
may
cause a short circuit and require
It
not wise to hurry the work, as
is
reconstruct
it if
The end
wood.
The two
eter,
and from f "
are
marked
the fibre strips,
reconstruction.
be necessary
to
any suitable piece
of
will
it
made out
of
supports for the secondary are 8" in diamto i" in thickness.
Eight equidistant points
on the periphery and
wide cut at these points.
These
its
careless.
supports are
off
least fault, such
other small similar mistakes,
See Fig.
slots J"
These
8.
on which the secondary
strips are 17" long
and
\" square
is
deep and
\"
slots are for
wound,
to
fit into.
and are cut from
the
best vulcanized fibre obtainable, eight being required.
In
each end of the strips a hole
to
recei^'e
end
is
drilled
a small brass screw, which
pieces.
A
wooden rod about
is
and countersunk
to fasten
i"
in
diameter
obtained and a shoulder turned on each end.
of the shoulder
is
\"
and
its
them
The
to the
is
now
diameter
length just equals the width of
24
The
the supports,
Oscillation Transformer
|"
i.e.,
if
The
used for the ends.
wood
f"
is
used, or i"
25
if
length of the rod over
i"
all
wood
is
must be
—
End Support for
S.
Secondary of Oscillation
Transformer.
Fig.
only 17".
See Fig. 10.
of each of the
end
A h" hole
is
now
drilled in the centre
These pieces are now slipped on,
pieces.
E
ITFig. 9.
— Fibre
one on each end of the rod.
supports, after fitting
them
Strip.
Screw the
in the slots
are parallel to the rod in the centre.
If
that they
any of the
strips are
77"
10.
— Centre
on the
and seeing
"TT
Fig.
fibre strips
Rod.
The Tcsia Coll
20
bent or warped they should be straightened before being
fastened in place.
A
good way
them
to straighten
is
to lay
them between two boards, placing some heavy weight on
the top board,
and lea\c them thus over
or 5 ounces of Xo. 28 B. &: S. gauge double cotton
About 4
covered copper wire
Two
first
method
18" long
in
\\'a\-s
of these
methods
be described,
as
satisfactory.
cylinder of
wood
turned out, and on
is first
will
intended for those that have a lathe
is
A
which the wire can be wound
them both
the authors have found
at their disposal.
There
required for the secondary.
is
are several equally good
on the frame.
The
night.
it
4" in diameter and
are screwed the eight
ends are in
strips of fibre, so that their
line,
and
that they
the amateur has a couple of clamps
strike
one another.
made
of strips of sheet iron with a bolt through the ends,
matters by clamping them around the
will greatly help
about 6" apart,
first
file
taken
order to
A
It
light cut
is
a
No. 18 thread
is
now
strips to within
cut, starting
an inch of
clean cut the tool
there
is
mounted on
the
the
In
must be \cry sharp and
several light cuts should be taken instead of one.
strips are
strips,
should be cut just as deep as possible.
make a
it
and then they are polished with
from the end of the
i"
other end.
A
and moving them as needed.
off the strips,
and sandpaper.
about
If
frame again
it
will
When
the
be seen that
a continuous groove in which the wires will
lie
with-
out touching one another.
The secondary frame
in
the
lathe so that
it
is
now supported between
just turns easily.
centres
Around one end
Oscillalion Transformer
Till'
wrap about
of one of the strips
be used for connections.
to
wire tightly on the
groove cut for
making
for
of shellac
A
this
is
dry
keeping the wire in the
When
all
finished, a
where they
gi\'en to the wires
is
is
wind the
extra should be left at
the connections.
When
strips.
i'
This
of Xo. 2S wire.
i'
Starting at this point
frame, always
About
it.
~i
the wire
is
rest
the end
hea\y coat
on the
fibre
heavily shellacked.
brush should be used so as not to displace any of
soft
The secondary should now be
the wires.
placed in a
warm
place to dry.
The
following method can be used in case a lathe
A
available.
around the secondary frame.
smoothl}'.
and shellacked
The
wire
is
make two
wrapped on
in place.
It
wood
wound
then
to
silk
It is
here that shellac dissoh'ed in
be used.
turns
tightl}',
thread
turns, to
is
is
wound on
keep them apart,
heavily shellacked
at the
^^'hen
should
not
on, starting about i"
same time between
it
and
might be mentioned
alcohol
from the end up to within an inch of the other end.
silk
not
spool of silk thread and some silk are re-
There must be enough
quired.
is
is all
and the frame put
wound
in a
warm
A
the
the wire
place to
thoroughly dry.
Get
t\vo pieces of
of each
J"xi2" pine 12" long and find the centre
by the intersection of
their diagonals.
points as centres describe two circles, with radii
on each board.
With
4I''
these
and 5^'
Di\"ide the circles ha\-ing the radius 5}"
into 36 equal parts.
These points can be located with a
protractor or mariner's compass, there being one e\ery 10°.
28
Tlie Tesla Coil
At each of these points
drill
boards cut out a piece i"x
At a planing
may
in
a \" hole.
See Fig. ii.
i".
buy eighteen
mill
dowels, 36" long.
-]"
gwe you
These
Each one should be
be had for one cent apiece.
two, which will
In each corner of these
\" rods,
thirty-six
cut
18" long.
Fasten one of the 12" end pieces to each of the ends of the
Sb- ^ holes
o
\
o
\
o
\
o
o
Ai
-5i-
I
o
v
\/,
,0^
^-o'
/^'
Fig, II.
— End
Support for Primary.
completed secondary frame, by four flat-headed brass screws.
See that the circular end pieces of the secondary just
the smaller circles
now
drawn on
the boards.
The
fit
on
^" rods are
driven into place, thus forming a circular cage on which
the primary
is
wound.
For the primary get an
i" wide.
8' piece of
No. 36 copper ribbon
AAYap the end of the ribbon once around the end
The
the dowel
of
A
Oscillation Transformer
shown
Fig.
in
29
and solder
12
in
it
piece of copper wire should also be soldered
Starting
from
here
on
place.
here.
two and a half turns around
take
—
Primary of Oscillation TRANSrORMER.
Fig. 12.
This
the secondary frame.
the
you
dowel
diametrically
Wrap
started.
and solder
it
the
in place.
will
bring you to the end of
opposite
the
dowel from which
ribbon once around
A
this
dowel
piece of wire should also be
—
Completed Sec13.
ondary or Oscillation
Fig.
Transformer.
soldered on.
spaced.
fasten
The
turns of the ribbon
Get four pieces of
them
the other,
as braces
should be equally
i"xi" pine
183"
long and
from the one end of the frame
to
the pieces fitting in the corners that were cut
out for them.
The Tcsla Coil
3°
J
I
I
I
I
- Bushings
for
Support of Oscillator
Standards.
^
/
~^
z
"¥"
-e
"^
4-
Fig. 15.
— Hard
Rubber Block on Oscillation Transformer.
The
Oscillation
Turn two bushings out
They
are
shown
the shoulder
centre,
at
and
is
The
A
I" thick.
two opposite points
Two pieces of
31
of a piece of f" brass or copper rod.
in Fig. 14.
the shoulder
Transformer
is
length over
§" hole
drilled
to recei\"e
and
is
slightly
V'
and
down
the
all is
drilled
countersunk
two small brass screws.
vulcanized fibre or ebonite J"xi'', 2" long, with
a 5" hole drilled h" from the end, are fastened to the middle
of the top side of the
made
The bushings
primary frame.
are fitted into the holes
and screwed
in place.
just
The
wires from the secondary are soldered onto these bushings.
^^'hen this
all
is
done the
that needs to be
oscillation transformer
done
is
to connect
completed oscillation transformer
is
it
up
is
finished
properly.
seen in plate III.
and
The
CHAPTER V
THE INTERRUPTER
Let
us
now
consider that important part of the apparatus,
The
the primary spark-gap.
stated, is to provide a
denser
charged to
is
function of
this,
as previously
path of high resistance until the con-
Then
capacity.
full
its
it
suddenly
breaks down, and allows the current to surge back and
across
it,
until the current
other factors
in
the
damped
is
After
circuit.
forth
out by resistance and
the
oscillations
ceased, the ideal spark-gap should return to
have
maximum
its
disruptive strength before the condenser can be charged by
the next cycle from the secondary of the transformer.
In practice
this
is
far
from being the
case.
The
air
between the discharging balls becomes heated, and
offers
a comparatively low-resistance path for the current.
This
results in
an arc being formed, which prevents the condenser
from performing
its
which confronts the designer
of
this
The
tially
is
to find
some way
to get rid
heated air and thus prevent the arc being formed.
object of this chapter
accomplishing
The
The mechanical problem
function.
is
to
this result,
show
several
ways
of par-
but in no case perfectly.
simplest form of spark-gap for the primary of the
oscillation
transformer,
one which has given
32
fair
results
Tlte Interrupter
^li
with the writers, consists of merely two adjustable brass
No
balls.
provision
made
is
for
blowing out the arc that
forms, so that considerable of the energy of the transformer
Nevertheless sufficient oscillations are set up
is
wasted.
to
bring the coil to within i" or 2" of
maximum
its
length of
spark discharge.
Most amateur
struction,
their
a designer
coil
is
be very anxious
work
apparatus
coil builders will, at this point in the con-
A
are.
may
what
to see
be obtained with the simple air-gap.
more acquainted with
is
the possibilities of
good idea of the working value of the
When
the workings of a Tesla
he can construct that one of the spark wipe-outs which
best suited to the current that he has at his disposal.
THE SIMPLE AIR-GAP
Two
standards of brass J" in diameter and 4" long are
mounted on a piece
5" apart.
A
each rod and
of
-^^" hole
is
hard rubber.
They should be about
drilled J"
from the upper end of
is
taped with a standard \" machine screw tap.
These two holes must be
Next two pieces
for the
whole of
standards.
Two
in line.
of \" brass rod 3!" in length are threaded
their length to
balls
Y
in
fit
the holes tapped in the
diameter are turned out of
brass or are procured
from a dealer
These
and threaded
Two
balls are drilled
to
in physical
fit
supplies.
in the brass rods.
vulcanized fiber rods are turned out of f" rod, 3" in
length,
and a
\" shield 2" in diameter
end of each handle.
The handle
is
is
drilled
screwed on one
and tapped
for
The Tcsla Coil
34
i" to
is
fit
on which
it
is
safeguard the operator's hand
to
fibre
the brass rod
screwed.
The
from sliding
shield
off
the
handle and coming into contact with the transformer
which would probably be
current,
fatal.
Connection can
be made to the brass standard near the bottom by
drilling
-6
-*Afcl*'
an
^
!_
IEHIImQ)
-^
J
'•
0/-/'A/-)'/'/-,
<-
e
.f
c
Fig. i6.
— Simple
Primary Air-cap.
a small hole through them, and then drilling and tapping
another hole at right angles to the
to
first,
for a
thumb
screw
bind the wire.
A
set
screw at the top of the standards to clamp the rods
in place after they
to the operator.
have been adjusted
See Fig. i6.
will
be a convenience
The Interrupter
35
THE AIR-BLAST INTERRUPTER
In order to
of
much
make
more
the air-gap
getting rid
efficient,
between the spark terminals, a
of the heated gases
mechanical means can be used of forcing in cold
driving out
much
To
higher.
efficiently
hard glass tubing
is
is
accomplish
drawn out
opening ^\" in diameter.
ard and
This
is
this
a nozzle having an
into
mounted on a brass standto a foot
used in the laboratory to operate a blast
is
lamp or any other suitable supply of compressed
good blast of air
to form,
thus
a piece of f"
connected by means of a rubber tube
bellows such as
air,
heated gases and keeping the resistance
the
will effectually
air.
A
wipe out any arc that tends
thereby increasing the disruptive length of the bright
oscillation
transformer discharge.
however, that
occupying so
it
is
The
a tedious task to
much
operator will find,
pump
a foot bellows,
of his time as to handicap
him
in per-
forming experiments with the high-frequency discharge, and
he will soon decide that the best policy
is
to construct either
a magnetic wipe-out or a motor-driven interrupter.
THE MAGNETIC INTERRUPTER
The magnetic blow-out
is
well suited for those
who have a
source of direct current at their disposal; either the
lighting circuit or
a suitable battery current.
have only the alternating current and
no- volt
For those who
who wish
to use the
magnetic wipe-out the writers have added to this chapter
a simple
home-made
electrolytic rectifier of their
own
design
The Tesla
36
which
will give
Coil
a current suitable for magnetizing the magnet
of this interrupter.
Two standards of the same
interrupter, but 6" in length
form as those used
and having spark
in the simple
balls I" instead
of J" in diameter, are mounted on a hard rubber base 10" x
The
fibre
terrupter.
handles and shields are also necessary for
Two
this in-
electromagnet bobbins 5^" long and having
an iron core |" in diameter with
An
are procured.
7".
iron
has 2 holes drilled in
it
heads 3" in diameter
fibre
yoke made from i"xj" iron
in the
the bobbins are fastened to
7" long
middle i^" from both ends, and
it
by a screw
in the core.
Two
polar pieces of f " square iron, filed into an egg-shaped point
The
are screwed to the upper ends of the core.
are wound
wire,
if
full
of
No. 14 B.
&
S.
gauge cotton-covered magnet
they are to be operated on a battery current of from
eight to ten volts such as a plunge battery.
rent of
rectifier
bobbins
1
10 volts
is
If
a direct cur-
available No. 24 should be used.
described at the end of this chapter
is
If the
used No.
22
wire should be used as the voltage of the rectified current on
no
volts alternating
is
about 90
volts.
be thoroughly saturated in order to
The magnets
must
give the best results.
After the magnets are finished they should be fastened
to
the hard rubber base, at right angles to the rods carrying
the spark balls,
balls of the
by two screws through the iron yoke.
The
spark-gap should be between the projections
of the magnet.
A
sheet of mica
is
bent around the polar
projections of the magnets in order to prevent the spark
from jumping
to the cores of the
magnets.
Fig. 17.
The Interrupter
of the coils are so connected that the current
The ends
them
will traverse
outer ter-
suitable binding-posts
and the
finished.
is
Fig.
The
The
in opposite directions.
minals are brought out to
interrupter
37
17.
— ^Maonitic
Inieehupter.
principle of this piece of apparatus
based on Da\'y's
is
experiment in which he found that the electric arc
is
extin-
guished upon the approach of a magnet.
THE MOTOR-DRIVEN INTERRUPTER
This interrupter
is
the one the writers used in their earlier
experiments with the 7" standard
part of this book.
It
consists
coil
described in the latter
run on the alternating current at
no
volts, driving
disc
having a number of projections bolted
face,
and a brass
separating
at will.
builder
it
oscillator so
may
direct current
mounted
from the projections on the
The motor may be
possess.
A
of
motor
essentially of a fan
a brass
around
its
that the distance
disc
can be varied
any suitable design that the
small battery motor rimning on
can be pressed into service
if
the amateur does
The Tesla Coil
38
not care to go to the expense of purchasing a fan motor or
The
has not the facihties for building one.
directions for
building a suitable induction motor are given at the end of
this chapter.
/bbei"
Fig. i8.
To make
— Motor
Interrupter Fan.
the disc for this interrupter turn out of \" sheet
brass a circular piece lo" in diameter.
may be
able
it
Lay
off
eter
on
its
no lathe
If
is
avail-
procured at a model maker's quite reasonably.
face
respectively.
two concentric
Di\ide
the
circles, 8"
inner
of
and 9}"
these
in diam-
into
thirty
equal divisions and draw radial lines from the centre of the
disc through each of the points
marked
o£F,
thus dividing
The
same number
the outer circle into the
through each of
Drill a hole
circles
A
and tap them
number
Interrupter
to
39
of equal divisions.
the points laid off
on both
a standard 4-36 machine screw.
jQt
made by bending
of brass angle pieces
I,
j'g"
brass
Two
holes
coontersunk
->i^
Brass Angle Piece.
into the
form shown
are drilled
flat'-headed
in the figure are procured.
and tapped
in
fit
a standard 4-36
pieces
are screwed to
each one to
machine screw.
These
the brass disc with j" screws.
A
\" hole
is
drilled in the centre of the disc
holes are drilled
on a
circle
and
having a radius of
three ig"
|".
Next
The Tesla Coil
40
turn out a circular block of hard rubber 2" in diameter and
the
same shape as
in
Fig. 20.
The
brass disc
is
screwed
with three brass wood screws {" long and the whole
to
it
is
fastened
the
to
insulated from
&
To
it.
%
shaft
of
the
motor so as
20,
plate a brush to bear
— Hard
Rubber Block.
on the back near the centre
of a piece of y^" sheet spring brass.
and
Y
be well
I
Fig.
10" long
to
mal<:e electrical contact with the brass
wide.
It is
is
cut out
This piece should be
mounted on a
piece of hard
rubber with a suitable binding-post, so as to press against
the back of the disc.
For the other side of the spark-gap a standard mounted
on hard rubber similar
spark-gap
is
to the
one described
used, but instead of being 4" long
for the simple
it is
6" in length
The Interrupter
and the brass
diameter.
The
ball
is
fibre
best
if
it
is
slightly less
41
than \" in
handle and shield are necessary in
order to adjust the length of spark-gap while the coil
operation.
—
r
is
in
The Interrupter
43
A SiLVLL SELF-ST.\RTIXG SDsGLE-PHASE IXDUCTIOX
MOTOR
To
build a motor, to run on the single-phase alternating
current of
perhaps
is
tools
no
running a fan interrupter,
volts, suitable for
ver}'
The
difficult.
builder will require
and a much greater knowledge
of
machine shop prac-
construct an efficient motor than to build
tice to
parts of Tesla apparatus combined.
had but
litde experience in
For those who have
an alternating-current fan
direct -current
batter}-
book may be complete
the coil builder will
have
all
The
motor.
following description of the building of this motor
in order that this
of the
all
motor construction, the writers
suggest that the amateur purchase
motor or a suitable
more
in itself
is
and
given
so that
the necessary data to build the
complete apparatus without reference to other works.
The
first
step in the construction
patterns for the base
to
make
the necessary
There are two castings
The
base supporting the punchinss for the stator
cast directly
on the standard which supports the motor.
required.
is
and yokes.
is
The
It
that
the
drawint;. Fig. 23. will give the required dimensions.
is
assumed that the amateur pattern-maker
an iron casting
mould was made,
is
therefore shrinkage
in the pattern in order to
enough.
One
is
aware
smaller than the pattern from which
must be allowed
be sure that the casting
eighth of an inch to the foot
is
will
for
be large
about the proper
amount.
Turn out a
circular piece
5
"
in diameter
and
i" in thick-
77/r
44
ncss.
Then a rod
i" in
'Icslii
('nil
diameter, and 6" long, swelling into
a graceful enlargement at the lower
enrl,
is
turned out and
fastened with glue and nails to the centre of the
<
in iilar disc.
-^
1-
-,'^
-
D-^
for jiUUifr heads
I'lO,
A
piece of
wood
the figure.
The
is
23,
PAn;.i':.'s oi'
YoKE.
cut out of ;" stock to the form
radius of curvature of the arr
so that the stator will
and nailed
—
fit it
accurately.
to the top of the upright.
This
shown
in
must be 2\"
jjiere is
The whole
glued
pattern
is
The Inlcmipter
iliilllllllilMI'Hliii
A
Fig.
;:4.
— Section
of Completed Motor.
45
Tlic
46
gi\cn two coals of
lampblack
to
make
of the rotor shaft
jet black.
'I'his
we must make
tompktt's
llic
pattern
castings are
of the stator.
and
of the
made from
They
a pattern lor a yoke.
turn out of \\" sloik a circular
we
this pattern
disc 5I" in diameter
Two
it
shellac \'arnisii, containing suOicicnt
In order to pro\i(le a su|)porl for (he bearing
for the base.
To make
l)csl
Tcsla Coil
same form
this palleni,
as in the drawing.
one
to
lit
each end
not only ser\e to furnish bearings
the rotor, but also to enclose the entire
for
motor and thus keep
out moisture and dust.
Vie.
25,
— Rotor
Disc,
After the patterns arc shellacked they should be sent to a
foundry where the castings can be obtained quite reasonably.
It requires
journal.
one casting of the base and two of the yoke
When
chipped and
The
all
the castings
arc obtained they should be
the roughness filed
rotor consists of a
or
number
off.
of iron discs 2\" in diameter
The
Interrupter
and having twelve f " holes
j^g"
thickness; about forty of
These
high.
discs can be
help of a lathe
and
around the edge and a
They should be made
hole in the centre.
j^|§Q-" in
drilled
47
made by
drill press,
A
sufficient
number
turned
down from a
shown
in the figure, to
motor
will not
is
or they can be obtained already
in electrical sup-
them are mounted on a
of
make
shaft,
As
a pile 2v" in height.
have a very heavy load thrown on
sufficient to
i"
f" rod of cold rolled steel to the size
not be necessary to key
fit
pile
the coil builder wfith the
stamped out from any of the large dealers
plies.
of iron about
them making a
them
A
to the shaft.
the
will
it
it,
good driving
They can be
keep them from turning.
in the figure.
The
conductors consist of twelve s" copper rods 2f" long.
One
clamped
in position
by the nut shown
of these rods should be driven in each of the holes
the edge of the discs
both sides.
To
and should
project J"
short-circuit them,
beyond them on
two heavy rings made
by bending two pieces of \" copper rod into a
an outside diameter of if" are soldered
rods.
in
Use
sufficient
solder
in
around
making
circle
having
to the
ends of the
these
connections
order to prevent heating at the connections by the induced
current in the rotor.
The
This completes the
next thing to consider
this case
is
rotor.
the stator punchings.
In
they will not be punched out, but will be cut out
on either a shaper or milling machine, or cut out by hand
after as
drilling.
much metal
has been removed as
The diameter
ing on Fig. 27.
of these discs
To make
is
is
possible
by
given in the draw-
them, cut roughly out of tHtt"
48
The Tesla Coil
hi
%k -%%.
o
"T
«)i»
I
s
o
^
The Interrupter
49
The Tesla Coil
JO
iron about loo pieces 6" in diameter, with a pair of snips.
A I" hole is drilled in the centre of them and the whole number
and turned
are clamped on a mandrel between two nuts
down
in
Next four
a lathe to si".
the figure,
and a
tube i" in external diameter and J"
fibre
internal diameter
Y' holes are drilled as in
driven in each hole.
is
length, with hexagonal nuts
and
A
J" stud 3I" in
f" iron washers, binds the
After tightening up the nuts the bolts can
discs together.
be slightly riveted to guard against possible loosening.
whole
is
clamped
either
a chuck and the centre
in
Next the
2f" in diameter.
slots are
is
bored out
A
file.
to
cut as in the figure,
on a milling machine or shaper or by the use
saw and
The
of a hack
large bulk of the metal can be
removed by
mounted on
the pedestal
drilling.
When
the stator
is
complete
it is
with four cap screws which screw into the bottom edge.
The two ends
are fastened to the stator with four l"
screws i" long.
way between
The
the nuts binding the stator discs together.
order that the heads
be drilled
The
fit
up against the
is
stator four holes should
next wrapped with paper until
and the heads are bolted on
are to be permanently.
It is well to
can always be put back
in the
same
between the shaft and the journal
of
In
to allow the nuts to project into the heads.
rotor
into the stator
grade
fillister
holes for these screws are drilled mid-
Babbit
metal
in the
mark them
place.
is
obtainable.
it
way
fits
they
so that they
Then
filled
just
the space
with the best
Cardboard washers
slipped over the shaft prevent the babbit from running out.
The
The
used
next thing to do
is
the size
are
No.
The
22.
shown
in
wrapped with
28.
'
is
wind
51
the stator coils.
wound
in a
The
wire
wooden frame
After the coils are
tape, shellacked,
wound
and allowed
to
of
they
dry by
Before the coils can be put into place,
means must be provided
This
to
coils are
Fig.
thoroughly baking.
is
Interruptef
for
making
the
motor
self-starting.
accomplished by means of a short-circuited copper
The Tesla Coil
52
The
pieces.
brought out
pieces
six coils are in series, the
to suitable
end terminals being
binding-posts fastened
and suitably insulated from
it.
A
end
to the
coating of black
paint completes the motor.
Although the induction motor
at varying loads,
we can
secure
is
a constant-speed motor
some
slight
speed regulation,
4Short circuited
of Wo,
14-
Bare
cortduc/br
Wi>«,
Cof>(>er
showing €haf]e of wire
bff[ore alijj^in^ into slots
Fig.
which
is
29
— Self-starting
Device.
a great advantage in operating the
by
coil,
inter-
posing a liquid resistance in series with the motor.
resistance consists essentially of
as
is
plates
suspended
in
an
cell,
ha\'ing
jar,
such
two metal
electrolyte, so that the distance be-
tween them can be varied at
erally
any suitable glass
used in a Daniell or Gra\'ity
This
used as the electrolyte.
will.
Copper sulphate
is
gen-
Plate
Plate
I\'.
\'.
— Motor-driven
— The
Interrupter.
Electrohnic Rectifier.
The Interrupter
53
AN ELECTROLYTIC CURRENT RECTIFIER
It
to
was only
make
that the authors decided
which has proven highly
rectifier,
advantages are that
Its
moment
public the results of their experiments on an electro-
current
lytic
at the last
it
easily
is
quires only slight attention,
its
efficiency
the current which a small set will rectify
To
a great
many
this description
it
may seem
The
the Tesla apparatus.
reasons
appeared, to the authors at
the
is
built,
very large.
is
is
entirely foreign to
circuits
will
if
need
about 80 or go volts pressure,
can hardly be obtained from the lighting
which are generally alternating or from
to substitute
however
for so doing,
least, sufficiently great, for
a source of direct current at
Then having
re-
very high, and
amateur constructs the magnetic wipe-out he
since this current
it
out of place in putting in
which
of a rectifier,
satisfactory.
and cheaply
he
this source of direct current
a D. C. motor
batteries.
will
for the induction
be able
motor de-
scribed in this chapter.
The
the
method
current
is
greater
due.
number
of rectifiers
now on
the
market use
of choking out the one half of the alternating-
wave and
The
it
is
to this fact that their
low efficiency
high efficiency of the apparatus devised by the
authors depends on what might be called the alternate path
connection or method; that
current to traverse, one of
is,
there are two paths for the
enormous
resistance
and one
of
very low resistance.
The
idea of this form of rectifier
came
to the authors in
The Tesla Coil
54
the
following
They were experimenting on some
way.
cathode tubes of peculiar construction, using a 12" induction
The
coil.
current from the secondary of this coil
latory in character, of course.
It
charge through the tube was
^-ery
was observed that the
unsteady, especially
the interruptions were not very rapid.
ments was carried out
effect,
to
oscil-
is
A
line
dis-
when
of experi-
determine the cause of this unusual'
with the result that the resistance was found to be
enormously greater for currents
in the
one direction through
the tube than in the opposite direction, due entirely to the
difference in the forms of the
two
electrodes.
After discovering this fact they wondered
lytic cell
if
some
electro-
might not be made which would possess the same
properties
and could be used
nating currents.
From
to rectify the
ordinary
a previous study of the
alter-
effects of
various electrodes on the electrolysis of certain solutions
we
arrived at se\'eral cells which exhibited these properties to
a marked extent.
It
tial
was found that an aluminium electrode was the
thing in every
of forming
cell,
together with
some acid
an oxide with aluminium.
The
salt
essen-
capable
other electrode
might be any conductor unaffected by the solution.
Some
of the conductors suitable for the other electrode
are iron, carbon,
gave more or
bonate,
acid
and
less
lead,
and the following
satisfactory results.
solutions
Acid sodium
sodium phosphate, acid potassium
car-
tartrate,
potassium alum, and in fact most of the ionizable,
acid sulphates, carbonates, tartrates,
all
and phosphates.
slightly
The Interrupter
By merely
putting one of these
method
this
gives
an
cells in
the circuit, the one
wave may be choked
half of the alternating current
But
55
Thus
than 50%.
efficiency of less
out.
the authors were led to devise the alternate-path method.
Before describing this method, however,
in detail the properties of a single cell.
we
After a current
passed for a few minutes through one of the
of oxide
tically
is
will take
cells,
While
this
does
is
prac-
not prevent the
difference of potential from being maintained across the
it
is
a coating
formed on the aluminium electrode which
a non-conductor.
up
cell,
does prevent the ions from giving up their charge and in
way
this
vanic
it
acts like a polarized copper plate in a single gal-
cell.
when
This
condition of
the aluminium
of the current the
is
enormous resistance
When on
the anode.
aluminium becomes the cathode there
merely the resistance of the electrolyte encountered.
possessing this property
cell
As stated
circuit
exists
the reversal
is
Any
called asymmetric.
before, a single cell
would choke out the one
by being merely put
in the
half of the alternating wave,
but as this gives an intermittent current, the following
the
method devised by the authors.
in all.
and one
The
Two
is
Three
is
cells
are needed
of these consist of one electrode of
aluminium
of iron, with a solution of
third has
between them.
sodium acid carbonate.
two aluminium plates and one iron plate
The same
On looking at Fig.
the current can flow
30
it
from
trolyte to plates I or 4.
solution
will
is
used.
be seen that when
E is positive
either plate 2 or 3 across the elec-
The path from
3 to 4
is
of
enormous
resistance, as the
I
to 2
6 to
aluminium
AA'hen
this
H becomes positive the current can flow from
or from s to 4.
7
the anode, but the path from
is
low resistance and hence the current takes
of
is
path.
is
Tcsla Coil
Tlic
56
It
takes the path from 6 to 7 as this
In this way both waves of the alternat-
of low resistance.
ing current are used
and the only
loss
is
due
to the resistance
of the electrolyte.
Thus
in
made
from
the direct current
which
has a sine wave form,
this set
the negative values in the alternating have been
all
positive.
The
following are plans for a rectifier suitable for use
on
directly
the
no- volt-alternating-current
light
The
rectifying cells have glass containing jars.
7"
X 6" X 4" inside
are cut out of
They
-J"
5" x 7"
are
sheet
and are
all
jars are all
The aluminium
measurements.
same
the
The
mains.
size
plates
and shape.
The aluminium
and four are required.
should be comparatively pure to prevent deterioration of
the plates due to local
action.
extent impure
may
rectify
it
will
the cells
are cut from I" sheet.
the
fail
be at a very low
Two
is
making
plates
it
larger
is
that
to.
The
third
is
plates are
is
8" x
iron plates
size as
This larger
5".
The
cell.
required to
necessity for
fasten the bind-
held three eighths of an inch
apart in the following manner:
canite or hard rubber (fibre
they do
if
goes between two aluminium
it
and the extra length
ing-post
The
them are the same
be used in the middle
to
work, and
to
efficiency.
of
aluminium plate and the
plate
the plates are to any
If
Out
of
some f" sheet
must not be used as
it
vul-
swells in
TJic Interrupter
water) cut four strips
x 61".
.1"
V'
These
latter pieces are drilled
Some
Also cut out four washers
diameter and a number of pieces h" square.
about
in
and tapped
The washers have a
\" thread.
\" vulcanite
threaded to
57
rod
up
cut
is
With
a \" nut.
fit
to
hole drilled in them.
into
about 2" lengths and
and washers
these strips
and
plates are held the required distance apart
firmly fasten
them
The
together.
across the tops of the plates
one of the
of each
A
electrodes are put
by the
solution
binding-post
As the
plates.
are longer
the plates
rubber are used
the washers at the bottom.
far superior to using iron ones
is
an insulating bushing.
The
strips of
the
the bolts
This method of using hard rubber bolts and
See Fig. 30.
nuts
and
a standard
fit
-}"
than
if
is
fitting
strips across the
the jars
top of
when
are wide;
on the edges of the
sodium acid carbonate
be a saturated solution.
them with
fastened at the top
the
they will be suspended in the
in place
strips resting
electrolyte,
and
jars.
used, should
is
Other solutions than
this
can be
used, although the authors obtained the best results with
this one.
Besides
it is
about the cheapest of
all
the possible
electrolytes.
In selecting an electrolyte the following factors must be
taken into consideration.
It
must have low
resistance,
must be a stable compound, and when no current
it
it
is
flowing
must not attack the aluminium plate and only
slightly
attack
it
when
To make
mounted
current
is
passing.
the set con\'enient to
in a
handle the jars should be
wooden frame, with
the cell containing the
The Tcsla Coil
58
-->fi'bai*
wojW
D.C,
A.c.
:;
r lauRE.
Fig
30.
ehowr'tig
— Rectifier
faos'ition
o£
1fia
ce)/5
and eledrtdcs
Plates and Wiring Diagram.
The
Interrupter
two aluminium electrodes
are
shown
With
59
in the middle.
The
in the figure.
this electrolyte the
few minutes,
it
aluminium
plates will
take a
The
form
in a
being merely necessary to short circuit the
D. C. taps with a resistance and allowing the
full
connections
rectifier
to
load current.
efficiency of the
apparatus will be somewhat increased
by using a cooling worm, as the electrolyte when cool has
the greatest current density.
It will
be necessary
to
depending on the use the
renew the
set
is
given
electrolyte at intervals,
CHAPTER
\T
THE CONSTRUCTION OF THE BOXES
The
is
next thing to consider in the building of a Tcsla
the boxes which contain the transformer
One box
coil.
for transformer, condenser,
might be used, but for a
coil
Two
be objectionable.
They
and
ha\'e the
A
up
inside
is
where they are
is
so
to the
placed on top of the box.
most substantial box, but
it
harder
is
filling
up
the pores
in
the
wood does
to
which
not sink
does in a softer wood.
it
the best material to use as the joints will require
which
pine
which lead
to the fact that the shellac \'arnish
considerable
oil,
is
the
safe, except those
oak with the same readiness as
Pine
if
advantage of taking
owing
tight,
used for
into
to handle,
of having all the high-potential connections
interrupter which
make
weight would
form can be used separately,
single box, however, has the
Oak makes
and high-tension
coil of this size the
advantage of not being too bulky
room and
less
and high-tension
separate boxes give the ideal result.
the transformer in this
desired.
coil
may
filling
will
up
to
make them
imper\-ious to paraffine
soak through almost anything in time.
Sugar
be readily stained and looks very neat when
\-ar-
nished.
For the
sides
and ends
of the transformer
60
box
it
requires
—
The Conslniclion of
the
Boxes
6i
a piece of straight-grained pine free from knots, ij" x lo",
6" long.
The bottom
26" long,
and
pieces to the size
The end
made
i"x
pieces
shown
in Fig. 31,
must be mortised
of a piece of
i
11", 2' long.
and plane
J" x 14",
Cut the
the edges true.
into the sides i"
from the
These tongues and grooves may be cut with a saw
end.
and
should be
the top of a piece of
chisel
TOP
a rabbeting plane
if
is
not at hand.
l/IEW-Tiivy rm^vtj
After the sides
COVER
-i'i'
Zoi"
iA
zsi-
-iSif'
0000
I®!
'®l
l@|
I®
i®|
I
I®
I©'
I®
i@|
I®
i@|
W
T
SIDE VIEW
END VIEW
'
Fig. 31.
Teansfokmer Box.
and ends are
finished the tongues
heavy coat of
shellac,
hol,
and while
still
and grooves are given a
which has been dissolved
wet are put together.
in grain alco-
Six long brass
screws with round heads are to be used in each board to hold
the sides.
A
on the screw
brass washer
to prevent the
Y
l^i
diameter should be placed
head from sinking into the wood.
Next the edges should be gone over with a plane
sary so that the
bottom board
will
fit
if
neces-
flush in all places.
The
62
Tcsla Coil
TJic
bottom board
that
it
is
be i" wider than the width of the box, so
to
laps over V'
is
cut to size,
a
finish,
on each
\\'\\tn the
side.
bottom board
the edges are rounded off with a plane to
and then
is
it
fastened to the box with long
headed brass screws, placed every four inches along the
A
and ends.
box
The
coating of shellac
is
ilat-
sides
given to the edges of the
bottom on,
just before putting the
gi\-e
to help
make
it
tight.
screws must be forced in until they are flush with the
wood.
Next
the inside should be given five or six coats of shellac,
paying especial care
each coat
A
to
to get
into the joints,
and allowing
dry before applying the next.
small brass cock in the end near the bottom
box
ience in emptying the
it
it
in so that the
box
of
will not leak
is
The box
for the high-frequency coil
of the transformer box.
working drawings
the condenser
it
oil.
oil.
and condenser must
partition
oscillation transformer,
should be bored in
circulation of the
A
is
construction as in the case
The dimensions
in Fig. 32.
and
its
a conven-
such that a siphon
quick enough for an occasional emptying of the
have the same care taken in
is
but the labor of putting
its oil,
are given in the
is
put in between
but several holes
near the bottom to allow of the
free
This box must also have several
coats of shellac, as the insulating oil used will leak through
in spite of all the precaution taken.
After the boxes are finished they should be stained or
varnished to suit the taste of the builder.
looks well, and as
it is
dark
it
covers
Walnut
up a multitude
stain
of faults
Boxes
63
boxes are well
made a good
The Construction of
in the
wood working.
ciling followed
by
If the
the
several coats of shellac
makes a very good
finish.
TOV VIEW
COVER REMOVED
COVER
.1
"?+=
h—
/?
ii
:=F^
-36?-
J6i
:^i
CHAPTER
VII
ASSEMBLING
It
for
not wise to hurry
is
the
if
when assembling
high-tension wires
brush-discharge effects will
are
the apparatus,
not properly insulated,
be noticed on operating.
In
nine cases out of ten poor insulation will result in puncturing his condenser
and probably burning out
Care should be taken
former.
mount
First
to
the transformer in
the transformer into
its
box bring
his trans-
follow these directions.
its
its
After lowering
box.
four primary leads to
The two
four heavy binding-posts on the end of the box.
terminals
inner
of
two sections are brought
the
to
two
adjacent binding-posts, and the two outer ones to the other
two, in such a
manner
that connecting electrically the two
middle binding-posts puts the sections in
circuiting the
See
the
two outer pairs throws the sections
diagram.
This
is
across two binding-posts, or
fits
and
short-
in parallel.
accomplished by means of a
piece of fiat brass with slots filed in
which
series
it
so that
it
just
fits
by a short piece of brass rod
in the holes of the binding-posts.
The secondary
terminals are soldered directly to two brass
rods f" in diameter and 3" long, which extend through the
opposite end of the box for ij".
64
These rods are insulated
Assembling
by two heavy hard rubber or
lows:
is
A
turned
full
2" piece of
down
diameter of the rod.
Fig. 33.
in the
The
A
§" hole
bushings
fibre
i^"
is
flange
them
and
as fol-
drilled
on one end the
down
the centre
bushinsrs should be a driving
— Connections
8"
made
rod 2" in diameter
fit
both
for Primary of Transformer.
end of the box and over the brass
are 6" apart
brings
fibre
hard rubber or
to iV', except for a
of the bushing.
65
up from
rod.
The
the bottom of the box.
well above the level of the
oil,
rods
This
thus assuring no
leakage at this point.
The
leads from the sections should be led to the brass
rods through glass tubing bent in the desired shape.
is
drilled
and tapped
in the
end of each rod
to
fit
A
hole
a standard
The Tesla Coil
66
Another hole
brass set screw.
the
first
drilled at right angles to
about \" from the end of the rod to meet the
This makes an
hole.
is
efficient
first
binding-post to hold the con-
ductor.
This
finishes the connections
can now be placed
box
is filled
former.
free
in the position
on the transformer, which
which
with enough pure paraffine
This
cover the trans-
oil to
should be of the best quality obtainable,
oil
from moisture and impurities, such as
lating purposes.
The
to occupy.
it is
It
is
used for insu-
should be allowed to soak into
The primary
sections for 24 hours before using.
all
the
terminals
are connected to a source of alternating current by means
of a suitable switch
The
next step
is
and
fuse capable of carrying 30 amperes.
putting in the connections
and terminals
in the high-tension box.
I
FiG. 34
- - h-
High-tension Bushing,
Three brass rods similar
box, with the
in the
end
same form
to those
used in the transformer
of bushings, are driven through holes
of the high-tension
oscillation transformer.
I
--
box next
to
one end of the
These holes should be about
from the bottom and 3" apart.
The
brass
6"
rods project
Assembling
The bushings and
I" williin the box.
tight
rods can be
made
oil
by giving them a good coating of Le Page's glue before
driving
A
67
them
into place.
2" strip of
wood
is
box below these rods,
glued on in the lower inside end of the
to
prevent the end of the oscillation
transformer from coming in contact with them.
i!.;.c:
Fig. .35,
The condenser
wire
to
'
*^
is
— Oscillators
is first
it
is
soldered.
glass tube suitably bent
the box.
A
wire
is
and Standards.
lowered into place in the box and a
run from one terminal
which
<J}
The
to the nearest outer brass rod,
wire should be enclosed in a
and should
follow the lower edge of
run from the other terminal of the con-
The Tesla Coil
68
denser in a similar manner to the other outer brass rod.
A
follows the other lower edge of the box.
from
this
of the
A
conductor at a point opposite
wire
is
also soldered to the
is
from the condenser lead
band and
led
oscilla-
Tlie tap wire
into place.
soldered to one end of the primary
the wire from the middle brass rod to the other end
of the band.
These leads should be run
They should
as directly as possible.
The
is
It
to be.
is
The
middle brass rod.
now lowered
is
where one terminal
primary band of the oscillation transformer
tion transformer
oil.
to
tap wire
in glass tubes
also be kept
and
under the
connections are shown in Fig. 36.
o
o
Fig. 36.
is
— Wiring
Diagram.
connections have been securely soldered the box
After
all
filled
with
oil,
so that the entire apparatus
is
completely
immersed.
The
Two
oscillators
fibre or
in length,
and standards can now be
hard rubber bushings 2]"
and having a
flange ]" thick
in
constructed.
diameter and
and
3" in diameter
turned on one end, are set in two holes cut in the
directly
above the holes
lation transformer.
A
in the brass
J" hole
is
bushings on the
drilled
i.\"
co\'er
oscil-
through the centre
Assemhling
Two
of each bushing.
tubes should
fit
J" brass rods 10" long are enclosed
The
The ends
the rods tightly.
rods project from the fibre
the bushings
diameter and gY'
in outside
in fibre tubes f"
on the
69
and can be
The
lo^ig-
of the brass
slightly tapered to
fit
oscillation transformer.
oscillators consist of
screwed on the end of two
two brass
balls i" in diameter
^f/' brass rods 12" long, which
are to slide easily in two holes drilled \" from the top of the
standards through both the fibre and the rod.
at the top of
each standard
will
A
set
screw
be of convenience in clamping
the rods in any desired position.
may be
In order that the discharge gap
the coil
in operation
is
are screwed
for
about
on the ends of the
in
diameter
rods, carrying the oscillators,
li".
the standards through the bushings in the cover
Slide
until the rods
make good
second box.
It
contact with the bushings on the
This completes the connections
oscillation transformer.
the
adjusted while
two vulcanite handles f"
now be
should
position at the high-tension
ing a space of about i^'
end
for
the
of
placed
the
in
its
in
final
transformer, leav-
interrupter between
the
two boxes.
The
built
particular form of interrupter which has already been
is
connected to the binding-posts of the high-tension
coil as in the
wiring diagram.
These leads and those from
the transformer to the high-tension
12 B.
& S.
est glass
box should be of No.
gauge hard copper wire and enclosed
tubing obtainable.
They should be
in the heavi-
as straight
and
The Tesla Coil
yo
as short as
is
safety in operating the
consistent with
pri-
mary spark-gap.
A
suitable
panel switchboard, with the necessary fuses,
transformer and
interrupter
acquisition to the apparatus, but
matter
makes a
sv/itches,
it
is
desirable
This
not essential.
left to the taste of the individual worker.
is
When
the connections have
has dri\en out
all
the air that
all
it
been made and the
can,
oil
open the interrupter
gap about i" and cautiously close the transformer switch.
If
no
excessi\'e load is
by the 30 ampere
in series,
closed
if
until
one
is
taken by the transformer as manifested
fuses or
an alternating-current ammeter
obtainable, the spark-gap can be slowly
the condenser discharges across
it.
Then,
if
the directions have been carefully followed in building the
apparatus, a heavy, bluish white, snapping discharge of over
12" in length will pass between the oscillators,
upon
the
further adjustment of the interrupter gap.
When
the transformer
is
used on 55 volts the primary
sections should be connected in parallel
in series.
parallel
If the sections
on
no
volts,
If
fault
may
it
ought
to,
no
volts
in
and hence the
con-
puncture.
by any chance a discharge should
may be due
be due
for
the voltage output of the secondary
would be about double what
denser
and
on the primary were connected
to several things.
to the fact that the sections
fail to
take place, the
In most cases
will
on the primary or secondary
of the transformer are connected in opposition.
mine whether the transformer
it
is
working
To
deter-
satisfactorily or
Assembling
not, disconnect
from the
it
-ji
apparatus and see
rest of the
if
an arc discharge of at least 6 or 8 inches can be drawn out
bet\\"een
and
color
This arc
two electrodes.
is
generally of a yellow
extinguished by any draught of
easily
you do not obtain a 6 or 8 inch arc
test the sections to see
they are connected in the right manner,
no arc
error has
is
it lies
does not
lie
in the transformer,
in the condenser;
charge, determined by
its
if
they are and
some
To
test this
is
most
If there
most
likely
connect the trans-
if
is
a condenser dis-
none obtained, your
likely short-circuited or
which can only be remedied by
its
even punctured,
reconstruction.
next place to look for trouble
is
in the oscillation
Ring out by means of a magneto the primary
transformer.
no open
circuits,
circuit bet«'een the
primary
and secondary
circuits to see that there are
and then
there
see
it is
bluish white color, can be obtained
primary spark-gap.
condenser
The
if
highly improbable, then
former up with the condenser and s;e
in the
and
If
been made in the construction.
If the fault
that
which
results,
still
air.
if
and
secondar}-.
due
to
is
any short
If these parts are all right the fault
may be
poor insulation, in having the turns of the secondary
touching.
The remedy
Finally look
and
is
ob^ious.
see that
aU the
electrical connections are
as they should be, then the apparatus cannot fail to discharge
over a 15" air-gap.
CHAPTER
VIII
THE THEORY OF THE TESLA COIL
Although,
the authors stated that
in the introduction,
they would not attempt to give a mathematical explanation
of the coil,
they feel that a few facts regarding the theory
still
would not be out
improvements
the
to the reader.
amateur wishes
The
as
of place here, in that
is
first
well
to
sets
It will also
suggest certain
be of assistance
own
the transformer.
is
The
Its action,
electro-
alternating current flowing in the
up an alternating magnetic
field,
which being
linked with the secondary induces an electromotive
in
it.
When
the secondary
is
open there
is
except
induction,
is
that
thrown on
necessary
its
magnetize
high
the
self-
core.
to the secondary, the current through
the primary automatically adjusts
is
to
force
theoretically no
current passing through the primary, due to
As a load
if
design.
almost everybody, depends on
magnetic induction.
primary
may
to construct a coil of his
thing to consider
known
it
itself
as the self-induction
decreased by the opposing ampere turns of the second-
ary, that
is,
if
the transformer
is
self-regulating for vary-
ing loads.
The normal
used
current through the primary of the transformer
in the 12" coil is
from 22
72
to 25
amperes, the secondary
Theory of
the Coil
voltage being about seventy-five hundred,
age in the secondary
To
-3
and thus
fifty-five volts
the amper-
oT-
get the required voltage of seventy-five
secondary on
to
about
is
73
in the
primary
hundred
it
in the
necessary
is
connect the two sections of the primary in parallel, as
this
On
has the effect of cutting the .primary turns in two.
one hundred and ten volts the sections are connected in
The
series.
use of the transformer in the Tesla apparatus
merely to charge a condenser, and thus
nary induction
coil or
even a
static
it is
is
seen that an ordi-
machine of the proper
dimensions could be used, but they are not nearly as handy.
Another important matter
tion of a transformer to be
tions
ary.
is
a
to secure
The
in connection with the construc-
used
for creating electric oscilla-
sufficiently small resistance in the second-
reason for this
is
that the transformer
is
used to
charge a condenser.
When an
electromotive force
a condenser, the
full
is
applied to the terminals of
difference of potential
is
not created
between the terminals of the condenser immediately, but
The time
rises gradually.
depends on
capacity (C)
its
charging circuit.
of the condenser,
in a
required to charge the condenser
and
The product
and
the resistance {R) of the
CR is called
the time constant
practically the condenser
time equal to ten times the time constant.
constant
is
to
is
charged
The
time
be reckoned as the product of the capacity
(Q
in
microfarads and the resistance {R) of the charging circuit
in
megohms.-
The
The
time
is
gi\en in fractions of a second.
condenser, more than anything
else, constitutes
the
The Tesla Coil
74
essential part of the Tesla coil.
It
plays the
same part
the mechanical interrupter in the ordinary induction
Its action,
lies in
however,
purely electrical and
up the currents
setting
When any
is
condenser
is
of
its
great advantage
enormous frequency.
may
discharged, the discharge
one of several forms, depending only on the three
constants of the discharging circuit
and
The
resistance.
discharge
as
coil.
take
electrical
— inductance, capacity,
may be
either oscillatory or
entirely unidirectional, consisting only of a gradual equali-
zation of the potentials on the two plates.
This
tration.
may
be
made
clear
by the following mechanical
Suppose a glass U-tube
to
illus-
be partly fdled with
mercury, and the mercury to be displaced so that the
one side of the tube
in
is
is
higher than in the other.
then a force due to the difference of
the liquid to return to
the mercury
that
so
it
is
is
now
level,
an equal height
in
allowed to return, but
released slowly,
position without oscillations.
it
If,
level
There
tending to cause
both limbs.
is
goes back to
If
constrained,
its
original
however, the constraint
is
suddenly removed, then owing to the inertia of the mercury
it
overshoots the position of equilibrium and oscilla-
tions are created.
If the
the liquid viscous,
being
damped out by
What we
these
is
rough in the
call inertia in material
resistance experienced
electrical
interior, or
oscillations will quickly subside,
friction.
with the inductance of an
the
tube
substances corresponds
electric circuit
and the
by a liquid moving
resistance of a circuit.
If
frictional
in the tube, with
we suppose
the
Theory of the Coil
U-tube
at
its
above
to include air
75
mercury and
tiie
would
circuit.
necessary conditions for the creation of mechanical
oscillations in
a material system or substance are that there
must be a self-recovering
the matter displaced
displaceability of
must possess
inertia;
some
in
kind,
and
other words,
moved must tend
to
go back to
the restraining force
is
removed, and must overshoot
the thing
when
be closed up
ends, the compressibility of the enclosed air
correspond to the electrical capacity in a
The
to
original position
its
the position of equilibrium in so doing.
Frictional resist-
ance causes decay in the amplitude of the oscillations by
dissipating their energy as heat.
In the same way the conditions for establishing
oscillations in a circuit
is
that
it
electrical
must connect two bodies
having electrical capacity with respect to each other, such
and the
as the plates of a condenser,
possess inductance
tions, the
and low
sudden release
circuit
Under
resistance.
itself
must
these condi-
of the electric strain results in the
production of an oscillatory electric current in the circuit,
provided the resistance of the circuit
critical value.
We
is
less
than a certain
have these conditions present when the
two coatings of a Leyden jar are connected by a heavy
copper wire.
Professor William
in
titled
Lord Kelvin, published
1853 a paper on "Transient Electric Currents" in which
the discharge of the
in
Thomson,
Leyden
jar
was mathematically treated
a manner that elucidated important
If
we consider
the case of a
facts.
Leyden jar or condenser charged
The Tesla Coil
76
through a circuit having inductance and resistance, then
in
up
in
the act of discharge the electrostatic energy stored
the condenser
is
con\'erted into electric current energy
dissipated as heat in the connecting
and
At any moment
circuit.
the rate of decrease of the energy in the jar
is
equal to the
rate of dissipation of the energy in the discharging circuit
plus the rate of change of the kinetic or magnetic energy
associated with the circuit.
From
Lord Kelvin
these facts
up an equation
sets
of
energy, vi^hich leads to a certain class of differential equation
The
solutions in this case
depend on
between the constants inductance,
resistance,
ha\ing two solutions.
relation
the
and capacity.
If
Z=
inductance,
C=
solutions are determined
If
is
4U
—
greater than
if
by the
—
LC
J^C
or
capacity,
that
,
R=
resistance, then the
relative values of
is, if
R
is
greater thanl/lr:,
V (J
T
is
—
R
greater than
4
,
the charge in the jar dies
gradually as the time increases, in such a
discharge current
The
charge
ratio
—
R
circuit,
stant {T')
is
is
is
is
called the
that the
time constant (Z) of the
CR
of the condenser circuit.
less
manner
away
always in one direction.
and the product
unidirectional
circuit
— and LC.
when
is
dis-
called the time con-
Hence
the discharge
the time constant of the inductive
than half the geometric
stants of the inductive circuit
mean
and condenser
of the time concircuit:
Theory of the Coil
however,
If,
—
77
T
(^ J?
is
than
less
4
—
R
the discharge current will
be oscillatory, the current decaying in accordance with the
damped
law of a
When
rent
oscillation train.
the discharge
is
so highly oscillatory that the cur-
not uniformly distributed through the cross-section
is
of the conductor, then the ordinary resistance (R)
and
ductance (L) must be replaced by the high-frequency
ance and inductance of the
circuit.
AA'hen the discharge takes the oscillatory
quency
is
R
is
son with
form the
fre-
given by the expression,
2-
If
in-
resist-
>
LC
can be neglected in compari-
very small, then
,
4L-
and then the frequenc}-
is
given by the expres-
sion,
In
this
equation both the quantities
in electromagnetic
C and L must be measured
units or both in practical units, viz., in
henrys and farads.
In the majority of cases
are practically used,
cuit
is
easily
negligible,
measured
which
in
the resistance
of
and the inductance
electric
the
is
small and hence
in centimeters or absolute C.
one milli-henry being equal
to
oscillations
oscillatory cir-
G.
S. units,
a million centimeters
(10°).
The Tesla Coil
78
Also
capacity
the
microfarad being
measured
best
is
microfarads; one
in
one millionth part of a farad or
the
IO-" of an absolute C. G.
S.,
unit
(electromagnetic)
of
capacity.
Hence when L
is
expressed in centimeters and
C
in micro-
farads, the expression for the natural frequency of the circuit
becomes
n=
X
1=
VCL
5.033
10"
storing capacity of a condenser
The energy
CV,
the expression -
where
C
is
given by
the capacity of the con-
is
2
V
denser and
The main
the charging voltage.
thing in constructing condensers to be used on
high charging voltages
all
is
the solid dielectric.
this
number
is
reduced when cost and internal energy
in
ebonite, mica,
tions,
are suitable,
constant
is
and
also great.
and micanite are
of these flint glass
high, being
Glass
from
is
is
5 to 10,
brittle,
loss
Glass of certain composi-
in the dielectric are considered.
is
There are
only a few dielectrics suitable for high-tension work, and
practically
the best, as
and
its
its
all
that
dielectric
dielectric strength
however, and liable to have
flaws which sooner or later give way.
The
capacity of a condenser depends on the area of the
plates, their distance apart
used,
and
farads,
is
where
and the constant
of the dielectric
expressed by the following formula in micro-
K
is
the dielectric constant,
the plates expressed in square centimeters,
apart in centimeters,
5
the total area of
and
D
the distance
Tlieory of the Coil
KS
^_
The
constant 9 x
lo'^
79
comes from the
one micro-
fact that
farad equals 900,000 electrostatic units of capacity.
The
oscillation transformer
construction are that
its
it
is
nothing but a modified trans-
The
former with an air core.
only important facts about
should be built to withstand great
between the turns, and that the primary
voltage differences
should have as small an inductance as
to
is
make
is
practicable, in order
No
the frequency as great as possible.
gained by having
many
close turns in the primary, because
the increase of inductive effect
increase in the
number
advantage
on the secondary, due
of primary turns,
is
to
an
about exactly
annulled by the decreased current through the primary due
to its
own
The
greater inductance.
function of the interrupter
may be formed
gap, for
if
The
to destroy
any arc that
across the terminals of the primary spark-
this arc is
not wiped out there will be no true
oscillatory discharge in the
one.
is
reason for this
is
condenser circuit or only a feeble
that as long as the arc discharge
continues, the secondary terminals of the transformer are
reduced to nearly the same potential, or at most
by a few hundred
The
volts.
function of the primary spark-gap
voltage to which to charge the condenser.
tial
difference
differ only
between the spark
balls
is
is
to regulate the
Since the poten-
almost equal
to the
potential difference across the condenser, the condenser will
discharge at a voltage determined by the length of the air-
The Tcsla Coil
8o
Now
gap.
there
is
suited for each coil
As a
rule
it
is
a certain length of spark-gap which
and
it
can easily be determined by
out until a point
it
trial.
ahnost reached,
is
out any further would cause
to cease pass-
it
This spark length almost always gives the best
ing.
best
best to start with a rather short spark-gap,
gradually lengthening
when opening
it
is
this chapter
In the earlier part of
it
was stated
results.
that the high-
frequency resistance and inductance should be substituted
and inductance, when dealing
for the ordinary resistance
with circuits which are subject to the action of electric
The processes and means used
lations.
ment
high-frequency measurements.
difference between the
two cases
The main
is
to
measure-
for the
and
potentials
when
applied to
of low-frequency alternating currents
are not always applicable or correct either
reason for the
be found in the
that a high-frequency current does not penetrate
merely a surface or skin
When
tra^'ersed
1.
The
is,
effect.
resistance of the conductor,
direct currents
five
be considered.
for high-frequency currents
that
into the
by an alternating current, there are
qualities of a circuit to
fact
conductor of good conductivity, but
interior of a thick solid
is
oscil-
which
is
always greater
than for the ordinary currents;
and alternating currents up
to
about a
frequency of loo per second.
2.
The
inductance of the conductor depends on
metrical form, material,
insulator.
The
tance becomes.
and the nature
its
geo-
of the surrounding
greater the frequency, the smaller the induc-
Theory of
3.
The
the Coil
capacity of the conductor, depending on
tion with regard to the return circuit
on the
4.
dielectric constant of the
The
8i
dielectric
and other
posi-
its
circuits
and
surrounding insulator.
conductance of the insulator surrounding
the conductor.
5.
The
energy dissipating power, due to other causes than
conductance, such as dielectric hysteresis, which exist in
Under
the dielectric.
this
heading comes the
from the brush discharges through the
air
loss of
energy
between the con-
ductors.
If
the constants of a circuit for low-frequency currents are
known, the values of the constants
be calculated
fairly correct.
can, however, be
delicate
measured
and inconvenient
isfactory.
The
directly,
for use
for high frequencies
can
high-frequency constants
but the apparatus
is
rather
and besides not always
If the coil builder cares to
sat-
measure the constants
of a circuit for himself, he will find the description of the
necessary instruments in other books as
it
is
beyond the
scope of this work.
Ha\-ing
now
briefly treated
theoretically
the principal parts, the authors will try to
parts
work
on
all
four of
show how
these
together to form the Tesla high-frequency appara-
tus.
The condenser
is
of the transformer
connected in series with the secondary
and thus
is
being continually charged.
\Vhen the potential difference betweeen the plates of the condenser reaches a certain critical value determined by the
length of the primary spark-gap, the diameter of the spark
The Tcsla Coil
82
balls, etc.,
a discharge takes place which oscillates through
and back and
the primary of the oscillation transformer
The frequency
forth across the primary spark-gap.
current depends entirely, as
of the circuit.
On
first
shown
thought, one
of the
on the constants
before,
would think
that the
condenser would discharge through the closed circuit in the
transformer secondary rather than
little
jump
the air-gap, but a
show
consideration of the matter will
that the induc-
tance of this circuit to electric oscillations of this nature
Another matter
so great that no discharge can take place.
that might be touched
gap.
on here
is
the resistance of the spark-
Before any discharge has passed and under normal
conditions the resistance of the spark-gap
voltage required to break
about 10,000.
air
After the
down one
initial
is
very great: the
centimeter of air being
discharge has passed and the
becomes heated and ionized the resistance may drop
low as two or three ohms.
part in the
The
is
damping
This
fact plays
as
an important
of the oscillation trains.
discharge from the condenser which oscillates through
the primary of the oscillation transformer sets
alternating magnetic
field,
is
rapidly
which being linked with the
ondary induces an electromotive force
induction in this case
up a
in
it.
The law
sec-
for the
not nearly as simple as in the case of
the ordinary transformer, the capacities of the circuits playing
an important
part.
If the capacity of the circuits is
certain critical value, the induction
capacities of the circuits, while
if
is
in the
below a
ratio of
the
greater the induction de-
pends on the relation between the number of turns in the
Theory of
primary and secondary.
voltage
The
the Coil
83
formulae for calculating the
difference across the secondary in either case are
extremely complex, involving the damping factor, the capacities
of the circuits,
and other
Drude and Bjerknes
constants.
have treated the subject of the oscillation transformer analytically in
an admirable maimer.
The frequency
of the spark in the large spark-gap
is
not a
simple one but consists of se\eral, one being the natural
period of vibration of the secondary and one a forced vibration of the secondary,
due
to the fact that the
secondary are never exactly in tune.
There
is
primary and
also a certain
small current of a high frequency, due entirely to the constants of the spark balls
and connectors, which act as a
condenser.
The Tesla
much
to
coil in its
present form
is still
be improved upon and wished
very crude leaving
for.
The problem
that presents itself in the construction of Tesla coils
tically the
same one
is
prac-
that presents itself in selective wireless
telegraphy, so that the solution of the one will solve the other.
CHAPTER
IX
USES OF THE COIL
The
Tesla
coil readily
lends
itself to
a great
number
of
experiments, some interesting in their effect, others useful
in
scientific
Waves
research.
X-Ray
be sent out into space,
illuminated,
number
The
brush
beautiful
of other things done.
high potential current obtained from this coil pos-
due
that are not possessed by either
a
static
in
which
to its high frequency
Ruhmkorff induction
the
machine.
These properties are best seen
effects,
may
shown, and a great
effects
sesses certain interesting properties
coil or
wireless messages
for
tubes excited, Geissler tubes
may
the Appendix.
in
the beautiful brush
be obtained even with the
coil described
All of these experiments
on the brush
discharge should be performed in the dark, as they then
show
to the best
These
effects,
advantage.
besides affording a
great scientific \alue.
non
is
and
it is
due
It is
a
known
pleasing sight, are of
fact that the
phenome-
molecules near the terminal,
to the agitation of the
thought, since the brush
is
hot, that
some heat must
be developed by the impact of the molecules against the
minal or each other.
A
little
84
ter-
consideration of the matter
Uses of the Coil
leads us to the conclusion that
which would give intense
much from
reason for putting
amateur new
The
suffi-
been
light
and
But
heat.
this is stray-
the practical nature of this book; the only
it
in being, that
it
might suggest
to the
lines for experiment.
following
have
we could but reach
if
enough frequencies, we could produce a brush
ciently high
ing too
85
on
experiments
from
taken
Nikola
brush
the
Tesla's
discharge
"Experiments
with Alternate Currents of High Potential and High Fre-
quency."
There
is
practically nothing except
some wire and a few
on the brush
supports
required for
discharge,
and thus they can be performed by every one.
the
first
all
these experiments
In
experiment two insulated wires about 10 feet long
are stretched across the room.
tances of a foot
and a
half
They
are supported at dis-
by insulating cords.
attached to each terminal of the
wires
is
coil is
put
in action the wires are seen to
coil.
One
of the
When
the
be strongly illumi-
nated by the streams issuing abundantly from their whole
surface.
(This experiment must be shown in the dark, of
course.)
The
cotton covering on the wire, although
it
may
be very thick, does not affect the result.
To
produce the best
of the wires
must be
effect the
carefully adjusted.
the wires at the start very long
cutting off
lengths
first
until
primary gap and the length
It is best to
take
and then adjust them by
long pieces and then shorter and shorter
the
correct
length
is
reached.
When
this
adjustment has been obtained and the wires are fed by either
The Tesla Coil
86
from them
the 12" or 7" coil, the hght
will
be
sufficient to
distinguish objects in the troom.
Another way of
brush
easily exhibiting the
by
effect is
attaching the end of 10 or 20 feet of No. 36 insulated copper
'
wire to the one terminal of the coil and the opposite end to
an insulating support,
lea\-ing the wire
hanging
clear.
Upon
touching the remaining terminal with a bit of metal held in
the hand, the wire will break forth into numberless streams
or threads of light palpitating in unison with the discharge
of the condenser.
The luminous
intensity of the streams
increased by focusing
illustrated
them upon a small
coil a
is
sphere.
The
is
ter-
wire bent into a circle about one foot in
centre of the sphere should be in a line at right
angles to the plane of the circle at
is
set up,
To
centre.
its
a luminous hollow cone
dark one half of the brass sphere
minated.
one of the
attached and to the other terminal a small brass
diameter
discharge
This
surface.
To
by the following experiment.
minals of the
in the
can be considerably
is
is
When
the
formed, and
seen strongly
illu-
get the best results possible with this experi-
ment, the area of the sphere should be equal to the area of
the wire.
Another way
may
be shown
in
is
which the luminous
effect of the discharge
as follows: two circles of rather stout wire,
one being about 32" in diameter and the other
and
to
each of the terminals of the
attached.
same
The two
plane.
When
circles
coil
12", are formed,
one of the
circles
must be concentric and
the coil
is
is
in the
turned on the whole space
Uses of the Coil
between the wires
uniformly
is
intensity of the streams
that objects in the
87
tilled
forming
this
room can be
The
with streams.
luminous disc
is
such
plainly distinguished even
though at a considerable distance.
By
this
time the experimenter will realize that to pass
ordinary luminous discharges through gases, no particular
degree of exhaustion
is
essential,
and
necessary, but a very high frequency
is
of course a
shows us that the attempts
of the molecules or
vacuum
atoms
the use of
sure.
is
when
to
need not be limited
be looked forward
light will
light
is
to the
to,
and
be produced without
any vessel whatever and with
When
This
high potential.
produce hght by the agitation
of a gas
tube, but the time
that in the near future,
to
fairly
air at
ordinary pres-
obtained this way, there will be no
chemical process nor consumption of material, but merely
a transfer of energy, and the probability
would have an
is
that such a light
efficiency far exceeding that of
of the present incandescent lights,
even the best
which waste so much of
the energy in heat.
The
Geissler effect can be readily
bui^nt-out incandescent globe, in
been destroyed.
To show
it
shown by using only a
which the vacuum has not
the bulb should be suspended
from an insulating knob, so that the discharge
through the centre of the bulb.
in order to see the
will pass
The room should be dark
changes that take place in the globe.
putting the coil in action the bulb lights
pulsating, delicate purple hue.
This color
generally turns to a lovely pale green,
up with a
in a
On
gently
few minutes
and then sometimes,
TJie
88
but rarely,
this
changes
tensity of the light
of the colors
is
something
minutes the filament
is
A
in-
discharge
it
is
peculiar thing always happens
is
found
used, namely, that in a few
to
be completely shattered.
it is
only necessary to hold the globe in the
hand, without any connections to the
By moving
The
be admired.
to
a bulb with a good filament
With
The
light.
too long through the tube as
liable to pierce the glass.
the 12" coil
white
to a delicate
not very great, but the delicateness
is
must not be continued
if
Tesla Coil
the bulb
around
coil, for it to light
up.
in the vicinity of the spark,
various changes in the intensity of the light will be seen.
If the
amateur
may
tubes, these
is
fortunate enough to possess
be
lit
up by connecting them,
an adjustable spark-gap,
coil
tubes will
to the coil.
some
Geissler
in series with
In the case of the large
light up when merely brought into the vicinity
of the discharge.
The
is
best X-ray tube to use with this Tesla coil
known
as a double-focus tube, although
may be used
of the
ing light,
coil
the terminals
X-ray tube are alternately cathode and anode, when
an alternating current
able,
what
any other tube
As
with not quite as good results.
is
if
X-rays
is
used the pulsating or rather
may be
called light,
va:ry-
would be objection-
but due to the high frequency of the current from
the pulsations are not noticeable.
focus tube
flector
is
used the rays are reflected
and then from the other
double the space
is
filled
tube had been used.
When
first
the double-
from one
in rapid succession,
with the rays than
if
this
re-
and thus
a single-focus
Uses of the Coil
If the
tube
12" coils,
it
is
a small one and
used on either the 7" or
is
should be connected in series with an adjustable
spark-gap, to prevent any injury to
this
On
it.
starting the coil
spark-gap should be open as far as possible and then
gradually closed until the best result
should be
it
89
felt
now and
then to see
becomes too hot the
is
if it
The
obtained.
tube
has become hot, and
if
should be stopped and the spark-
coil
gap lengthened.
may
For those amateurs who
desire to use this coil for
wireless telegraphy, the authors merely state that
able,
is
it
suit-
with a few minor changes, in most of the systems using
For
a step-up transformer.
referred to a large
number
detail
information they are
of admirable books, especially
devoted to this subject, written by very eminent
men
in this
field.
But
opens
after all the great field of experimental investigation
itself to
enter the realm
the possessors of one of these coils
first
the field in
is,
field
of electric waves.
The
subject
results are expected
itself is still in its
when
netic disturbances are verified in
It is
infancy
the laws of electromag-
a convincing manner.
not the easiest subject to experiment in by any means,
on the other hand
it is
the
most
difficult.
In order to carry out any of the experiments at
satisfactory results a large
and
they
which Hertz made himself famous, the
that
and great
when
mathematically investigated by Maxwell;
electric
wiring
is
room
required.
of a large barn, provided
free
A
from
all
all
and
get
metallic objects
good place
is
in the loft
no better place can be had.
It
The Tesla Coil
QO
was
in a large
barn that the authors verified some of Hertz's
experiments on electric
In dealing with
waves.
waves there are two disturbances
to
be taken into account,
the electromagnetic and the electrostatic.
two
on
ing both
which
is
the
all
wires.
A
method
electromagnetic and
also
sta-
be given for obtain-
will
stationary
the
that can consistently be
There are
waves and the
classes of waves, the electromagnetic
tionary waves
electric
waves,
brought within
the
scope of this work.
D. E. Jones has made a translation from the German
of the original papers of Heinrich Hertz, dealing with the
experiments and results which have
The
knobs a short distance apart.
to the
his
name famous.
radiator or oscillator used by Hertz consists of two
metallic plates, having attached to
in
made
secondary of the
coil.
them short rods ending
These knobs are connected
Hence, as the secondary
motive force accumulates, the plates are brought
ence of potential and lines of
stretch out
We
sponding points on the negative.
a
differ-
displacement
electrostatic
from the positive side of the
to
electro-
oscillator to corre-
have thus a strong
electrostatic displacement created along the lines of force.
When
the potential dilTerence reaches a certain point de-
pending on the length of the spark-gap, the
breaks
down and a
air
current flows from the one
other across the spark-gap.
It is
insulation
plate to the
merely the discharge of
a condenser, for the two plates on the oscillator form a condenser, with air as a dielectric.
around a magnetic
This creates in the space
flux, the direction of
which
is
everywhere
Uses of the Coil
normal
91
The
to the direction of the electric displacement.
energy
electrostatic
is
thus transformed into electrokinetic
energy.
the
If
some
of the energy
As the
intermittent
this
is
way
sufficiently
therefore
we have groups
the electromagnetic waves are set
In order to
of
trains
which spread out through the
off
have the breaking
sudden
a displacement wa\e.
off as
in operation
and
oscillations
started
is
thrown
coil is continually
waves thrown
In
oscillation
electric
down
up
of
electric
dielectric.
in the air.
of the air sufficiently
sharp to obtain the oscillations, at least three things are
necessary: the spark-ball surfaces
no
ultra-violet light
must
fall
must be bright and
on the
balls,
and the
clean,
balls
must
be a certain distance apart, best determined by experience.
The form
of resonator de\ised
by Hertz consists merely
of a nearly closed ring or rectangle of wire the ends of which
end in metallic
balls placed very close together.
ball is adjustable
have been
many
The one
by the use of a micrometer screw.
modifications of this resonator,
the authors found
most
satisfactory
There
but the one
was where a neon or
carbon dioxide Geissler tube of the spectrum variety was
connected directly across the spark-gap.
Instead of getting
a spark then the tube becomes illuminated.
By
tor,
using this resonator and the before-meintioned oscilla-
the magnitude of the electric displacements in the space
surrounding the oscillator can be
Hertz's great
air.
This
is
work was
mapped
in setting
out.
up stationary waves
in
accomplished by having a large metal plate
The Tcsla Coil
92
set
up
in the
radiator
is
set
room
up
to act as
in front of
a
it,
reflector.
at
By
reflector the
The
this
with
is
it,
its
so
parallel to the
holding the resonator parallel to the metallic
nodes and antinodes can be easily traced out.
size of the plates
on the radiator used by Hertz
The
experiment was i6" square.
of about
coil
some distance from
that the plane of the plates on the oscillator
reflector.
The
No. 6 copper wire, 14"
m
in
resonator was a ring
in diameter.
n
w
a^
Fig. 37.
To
used.
set
— Waves
on Wires.
up stationary waves on wires
Two similar
plates to those
the
on the
same radiator
is
oscillator are gotten
Uses of
tlie
Coil
93
and mounted a short distance from the plates of the radiator.
The
plates are all parallel
and have two
from them across the room as shown
Thus
the wires
are
parallel wires led
in the figure.
electrostatically
connected
to
the
Hertz radiator and the plates rapidly alternate in potential,
and
this
applies to the ends of
This
electromotive force.
potential
which
If the
light.
tionary
the
EMF
wires
creates
an alternating
electric
waves of
travel along the wires with the velocity of
length of the wire
waves of
electric current
is
suitably adjusted, sta-
and potential are
set
up
by the interference of the direct and reflected waves.
To
tion
try the
and
interference of electric waves,
two brass rods ending
consisting of
in a zinc
box
must be very
tained.
experiments on reflection, refraction polariza-
of parabolic
form
is
in balls
required.
sensitive, for otherwise
The prisms and
a small oscillator
no
lenses used are
and mounted
The
resonator
results will
be ob-
moulded from
either
paraffine or pitch.
As before stated the authors
said that they
would merely
outline the experiments possible with the Tesla coil,
and
for
the detailed information the translations of Hertz's original
works must be consulted, unless the amateur has
knowledge of German
course be far
more
to
sufficient
read the originals, which will of
satisfactory.
There are several experiments which can be readily performed with
this
apparatus and which would appeal to those
having no knowledge of electric phenomena.
ments have but
little
practical value,
These experi-
the only reason for
The Tesla Coil
94
them being
citing
some
that they
may
who should chance
friend
furnish entertainment to
The
into his shop.
writers
saw them performed on the vaudeville stage with an
first
Oudin resonator which
To
is
far inferior to the Tesla coil.
begin the performance the operator should
make a
few general statements as to the voltage required to leap
such as 30,000 for
different air-gaps,
Then show
2", etc.
and
After he has
about 55,000
for
the discharge across the 6" or 12" gap
the spectator imagine
let
i",
what voltage that
represents.
become somewhat impressed with the
intensity
of the discharge, the operator can approach one of the oscil-
and allow
lators
this
his
hand
when
motion
in constant
There
point.
this current
effects result so
is
To
his bare hand.
without severe burning of the hand, he should keep
do
on one
on
the spark to play
is
is
prevent the spark from playing
only a very slight sensation
traversing your
body and no
shown
The
next experiment
felt
injurious
The
the authors are aware.
far as
best
hand when
to
effect
in the dark.
the coil
is
is
one
to grasp
in operation
and
oscillator with the
to
have an assistant
touch the operator's bare elbow with a cotton cloth dipped
in alcohol.
To
The handkerchief immediately
get the result without
rather
tightly
bursts in flame.
any uncertainty the cloth
around the
assistant's
modification of the same experiment
is
hand.
any of the audience are inclined
as to lighting cigars
to
An
wrapped
amusing
to touch the cloth to
the hair of the operator, showing that the hair
If
is
is
not ignited.
smoke, a suggestion
on a windy night without the annoyance
Uses of the Coil
of
matches blowing out
95
The
will be greatly appreciated.
operator has merely to bring a piece of metal, such as a nail,
held in the
and
hand
to within h" of
light the cigar
A
one of the spark terminals
from the spark.
gas flame can be
lit
with the bare fingers by grasping
one oscillator with the bare hand and approaching the burner
with the finger of the other hand so that a spark will
The
the metal tip of the burner.
more spectacular by
letting the
jump
have made
A^riters
spark jump from the
to
this
tip of
the tongue.
In these experiments an assistant should adjust the spark-
gap so that no more current passes than
is
to
To
is
necessary.
This
prevent the spark from burning the operator.
convince
the
audience of
the
tremendous voltage
passing through the operator's body he has merely to bring
one hand up to a lighted incandescent globe, while he grasps
one terminal of the
coil
On
with the other hand.
approach of the hand the filament
the near
will violently vibrate
and
then shatter, blackening the bulb and of course extinguishing
the lamp.
Lighting Geissler tubes held in the hand or even in the
mouth by approaching them
ment
to the oscillators
is
an experi-
that never fails to bring forth the applause of those
present.
Perhaps the most spectacular experiment, one which
unaccountable for by the every-day electrician
house wiring and has never been brought
high-frequency- currents
is
the lighting of
in
is
who does
touch with
an ordinary incan-
The Tesla Coil
96
descent lamp with
traversing
current
the
the
operator's
body.
Before performing this
experiment some few remarks
on the quantity of current necessary
to full brightness
on the no- volt
to bring the filament
circuits
should be made,
They can
those present are ignorant of electrical matters.
if
thus see that the energy
C. P. lamp
therefore
is
\olts this
equivalent to 55 watts,
is
and
that this
means approximately
The
^^
reason
taken with impunity
is
of an
why
\
no
ampere, while according
ampere
this
amount
At
taken through the operator's body.
to the best authorities
age human.
an ordinary 16
required to light
is fatal
amount
to the aver-
of energy can be
not definitely known, but
it is
thought
be due to the fact that the high-frequency current does
to
not penetrate into the interior of a solid conductor, but
follows the surface.
The
This
is
known
as the skin effect.
operator, to get the best results, should stand on an
insulated stool
and grasp one terminal
of the coil with one
hand, and approach with a piece of metal held tightly in the
hand or mouth one lead
of a lamp, the other lead of
has been previously grounded.
to bright red
gap
up
to
its
and
if
an
The lamp
assistant adjusts the
best working distance, the
to full brightness.
will
which
come up
primary spark-
lamp may be brought
Plate VI.
— Discharge from
Plate VII.
— The
the 12" Coil.
7" Standard Apparatus.
CHAPTER X
DIMENSIONS OF
For
think
chapters,
spark
amateurs
those
is
7"
who,
STANDARD COIL
ha\'ing
read
previous
the
an apparatus giving a twelve-inch
that
too large for
their
limited uses, this chapter has
been added.
This
coil
is
by no means
to
be thought of as a toy, for the
authors themselves used the very apparatus described in
this
chapter in carrying out their
X-ray and Geissler tubes.
first
experiments with the
Wireless messages were also
sent successfully over a distance of three miles in
wet weather.
This was the greatest available distance over which the
authors could try the
coil,
so that three miles should not be
maximum
considered the
In clear
transmitting distance.
weather messages could easily be sent a distance of about
fifty
miles, provided
your antennae
is
well insulated
from
grounds.
Because
does
not
apparatus
this
mean
regards insulation
entirely
on
this
that
is
any
not as powerful as the other,
less
care should be
and mechanical construction,
whether the
coil builder is to get
mittent spark or a fat crackling one.
between
this
for
The
taken
it
as
depends
a thin, inter-
only difference
apparatus and the larger one, besides that of
97
The Tesla Coil
98
size, is in the
construction of the transformer
and then they are only
The
built
trivial.
core of the transformer
up
of pieces of
long after the
is
&
No. 32 B.
manner described
in
care should be taken in annealing
wires as
was done
The primary
is
38.
2f" in diameter
S.
and
is
gauge iron wire 13"
Chapter
II.
The same
and insulating the
iron
before.
wound
other, as seen in Fig. 38.
Fig
and condenser
— Primary
in
two sections adjacent
Each
section
is
to each
wound towards
and Core of Transpoemer of
7" Coil.
the centre, starting i" from the ends of the core, for a distance
of 5".
There are
six layers of
No. 16 B.
& S.
cotton covered copper wire in each section.
thoroughly shellacked
are held
At
least
when put on and
left for
layer
is
the terminal wires
by the same method as described
two feet should be
gauge double
Each
in
Chapter
II.
bringing out the terminals
to the binding-posts.
The secondary
is
wound
in
two sections.
gauge double cotton covered copper wire
is
No. 32 B.
& S.
The
tube
used.
Dimensions of
on which
wound
it is
thickness of the wall
Standard Coil
99
has an internal diameter of 4" and the
It is 11"
^^".
is
They
are 6" in diameter
4g" in diameter cut out of the centre.
made from
long and
The bobbin heads
the best vulcanized fibre.
of j" sheet fibre.
7"
are cut out
and have a hole
Four of these are
w^ II
^^--^^—^4^11 -4^
!
Fig. 39,
They
shown
the
in the
->'i^
7" Coil,
are slipped on the tube to the positions
The
figure.
heads of each section
two sections
-^i-
Secondary Bobbin of Transformer of
-
required.
in
J
2}/'.
is
3 J",
distance between
and
The bobbin heads can be
same manner
bobbin
the
the distance between the
held in place
by cutting
as described in Chapter II
the rings out of a very thin fibre tube, or in this case
it
will
be sufficient to wrap some heavy brown paper several times
around the tube between the bobbin heads.
a layer on the secondary, shellac
turn of paper.
\" of the
In
this
way
bobbin heads.
it
After winding
and wrap
it
with one
build up the secondary to within
When
the last layer
is
put on
it
The Tesla Coil
loo
wrapped with
is
several turns of paper
which
is
shellacked
This completes the construction of the transformer.
in place.
\A'hen finished
it
should be
left for
some time
in a
warm
dry
place as behind the stove, to thoroughly dry the shellac.
The
reason for this
is
that green shellac
a
is
fairly
good con-
ductor.
For the condenser, twenty-eight sheets of brass 6" x lo"
are required.
No. 32 or 34
sheet has a lug i^' long
on
it
soft sheet brass
and i]" wide
is
Each
used.
either cut direcdy
Whether they
or soldered on in the upper corner.
are cut directly on the sheet or are soldered on will depend
on the width
are cut
lip is
\Mth
of the brass sheet used.
on the sheet or soldered on with 8"
and
7"
is
liable sooner or later to give
reconstruction of the condenser.
clean before putting
The frame
is
made
Any
should be rejected
way, thus causing the
Wipe each
sheet of glass
in to the condenser.
The
constructed from well seasoned pine.
two sides are made
is
it
it
i"
Thirty
x 12" are required.
sheet of glass that has an air bubble in
it
A
brass.
See Fig. 40.
bent across the top of each lug.
sheets of glass -^q" thick
as
12" brass they
from J" x 12" pine 4" long.
of a piece of I" x 4" pine 8" long.
The
The base
tened to the sides by some flat-headed brass screws.
is
base
fas-
The
heads of the screws should be sunk flush with the wood.
On
the one side of the frame two strips J" x i" are fastened;
one at the top and the other at the bottom of the frame.
See figure.
the side
The frame
on which the
is
now
strips
laid
on a
flat
surface with
have just been fastened down.
Dimensions of
I
7"
S/andard Coil
t::
f^l" Sirijit
I
I
^it'^l'strik
I
I
I
I
>
I
^
i^Cstrl^
--3"
.
^
^
Fig, 40.
— Plate
and Frame of Condensek.
lOI
The Tesla Coil
102
A
glass plate
is
placed in the frame after having been wiped
dry and clean so that
Then a
brass sheet
glass at the
should just
is
touches the bottom of the frame.
it
laid in so that there
i"
is
bottom and a V' margin on the
margin of
The
sides.
fit
lip
Without
against the upper edge of the glass.
displacing the brass sheet place a sheet of glass on top of
This
it.
the lug
is
followed with a sheet of brass, but in this case
on the brass
the previous one.
to
brought out on the opposite side
is
Continue
this
process until the 28
Two
sheets of glass have been put in place.
are placed on top of the last brass sheet.
glass sheets
Also remember
to bring the lugs from the brass sheets out on alternate sides.
Mortices should be cut in the top and bottom of the upper
ends of the sides a
last
little
deeper than the point to which the
These are
glass sheet reaches.
of pine l" X i" similar to those
should be screwed
the glass.
strip
A
and the
down
in turn
down
These
piece of paper or cloth placed between the
and solder a piece
of copper
already been tinned, to each of the
the one side
and another wire
About No. 16 bare wire
side.
extra wire should be left to
The
receive two strips
other side.
glass will prevent the breaking of the latter.
which has
on the other
to
tjie
so that they press firmly against
Set the condenser upright
wire,
on
oscillation
make
transformer
is
all
lips
to all the lips
will do.
Enough
necessary connections.
constructed in the same
manner
as the one for the 12"
for the
secondary are 6" in diameter and are turned out
of i" material.
coil.
Eight equidistant
The
circular supports
slots are cut in
the per-
Dimensions of
iphery
Y
square.
long.
A
rod 11" long
the
figure 41.
The
f'
Standard Coil
square and 11"
fibre strips are A"
is
turned out
103
to the
size
shown
in
diameter and has a A" shoulder
It is i" in
turned on each end.
This rod holds the two supports for
the secondary apart.
If the
grooves
of winding the wire in
should be cut on the fibre
to be used, the thread
is
strips before
mounting them on the supports.
In the original
coil the
wire was merely
wound on
three
supports 3" wide mounted on a hexagonal end piece.
fibre
The wire was wound
contact
this
method
it
adjacent turns were
and the whole was thoroughly shellacked.
method
new,
that no
so
of
winding gave good
in
Although
results while the coil
was
was found after some usage that the wires became
loosened, thereby reducing the effecti\-e sparking distance.
A
better
way
howe\-er,
is
to use
The
scribed in Chapter 1\.
one of the methods de-
wire used
is
Xo. 28 B.
gauge double cotton covered copper wire and was
&
S.
wound
18 turns to the inch.
The end
pieces for the primary are cut out of h" material
The
and are 9" square.
dowels
fit
used in
all.
is 8".
diameter of the
After the secondary
The
which the
There are twenty -four \" maple dowels
is
are screwed to the secondary frame,
in place.
circle in
wound
and
these end pieces
the dowels slipped
length of the frame o^'e^
all
is
The
12"
primary winding consists of one and a half turns of a copper
ribbon
-i"
wide.
The
the ^^'inding stretch
other,
A
turns should be equally spaced
from the one end of the frame
copper wire
is
and
to the
soldered on to each end of
the
The Tesla Coil
104
UJ
-*IT'-|
T.OC
I
r
—
T-
I
1
o
,
f„0
1^
I-
t3
DC
(I
'
I
to
°
'^
I
"-•
I
U=-i
I
'
"^
K
IP
il-jt
I
— -^
i^;
(Jj
CO
-^J'
«
o
i4
Ti
is!
H
z
o
ii
--./
4
^
g^
f
Dimensions of
primary band for making
i"x|", 12" long,
strip
tiie
is
Standard Coil
105
A
hard rubber
connections.
screwed across the top of the
Two
completed oscillation transformer.
in
it
8-y apart.
holes are drilled
Into these two bushings, similar to those
used in the 12" coil and described in Chapter IV, are
When
the secondary terminals are soldered to
oscillation transformer
is
mounted
in
seasoned oak.
Chapter VI apply
cover
is
The box
is
All the directions given
The
divided into two halves, one carrying the interrupter
oscillators.
connections from the interrupter to the condenser are
made through
the hinges so that the cover
without disturbing the connections.
A
may
of holes drilled in
it
of the box.
It
is
It
is
put in be-
has a
number
to allow of the free circulation of the
Suitable handles are put at each end of the
transformer
be swung back
partition
tween the transformer and the condenser.
The
The
to the construction of this box.
and the other the discharge
The
the
one box.
dimensions of this box are given in Fig. 42.
in
them
complete.
All the parts of the 7" coil are
built out of f" well
fitted.
is
now
set
on end
box
oil.
for carrying
it.
in the smaller division
held in place by two yoke-shaped,
supports fastened to the inside of the box
and
core between the two sections of the secondary.
wooden
encircling the
The primary
terminals are brought to four heavy binding-posts at the upper
end of the box.
They should be
soldered on in the
order as for the transformer on the large
shorting, the
coil,
two middle posts puts the sections
that
is,
same
so that
in series
shorting the two outer pairs gives a parallel connection.
and
Tlie Tesla Coil
roo
K
>
Dimensions of
The condenser and
in place,
Standard Coil
7"
oscillation transformer are
is
sec-
in glass tubes,
From one
suitably bent, directly to the condenser.
condenser a wire
now put
The
between the two.
the condenser being
ondary terminals from the transformer are led
the
107
side of
an end of the primary band
led to
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.
should be of about No. 20 B.
in glass tubes
& S.
They
gauge copper wire, enclosed
and kept under the
oil
as
much
as possible.
o
o
Fig. 43.
— Wiring
Any one of the forms of
V can be used with the coil;
Diagram.
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 lying
in grooves cut in the
I"
under side of the cover.
A
piece of
hard rubber sheet should be screwed over the grooves
wherever there
transformer
shown
or
is
any danger
of shorting to the core of the
primary terminals.
in the wiring
diagram.
The
connections
are
io8
Tcsla Coll
TJic
The
two brass
oscillators consist of
screwed on the end of two
rods 7" long, which are
-^^" brass
from the top of the
drilled \"
two holes
to slide easily in
standards, through both the
fibre
diameter
balls J" in
and
the rod.
A
set
screw
at the top of each standard will be of convenience in clamping
the rods in any desired position.
The standards
Two
are constructed as follows.
hard rubber bushings 2" in diameter and iV'
having a flange \" thick and 2^"
end are
set in
is
and
diameter turned on one
in
two holes cut in the cover directly abo^•e the
on the
holes in the brass bushings
A I" hole
fibre or
in length
oscillation transformer.
Two
through the centre of each bushing.
drilled
f " brass rods 8" long are enclosed in fibre tubes f " in outside
diameter
and
7 V'
The ends
tightly.
and should be
The
long.
should
tubes
of the brass rods project
tapered to
slightly
fit
fit
the
from the
the bushings
rods
fibre
on the
oscillation transformer.
may
In order that the discharge gap
the coil
is
in operation,
are screwed
for
about
The
two
on the ends of the
be adjusted while
handles I" in diameter
rods, carrying the oscillators,
i\".
standards are
cover until they
now
slid
make good
the oscillation transformer.
up
^'ulcanite
through the bushings in the
contact with the bushings on
When
to the alternating current
the coil
mains,
it
is
will
now connected
break forth
in
may
be
a beautiful 7" discharge.
If
everything
found
in the
is
not as
it
ought
manner described
in
to be, the trouble
Chapter VII.
-
Dimensions of 7" Standard Coil
7
i
f
m§$$^^^
5
\-
Oscillator **«
i
%5tandar.i>
7 Coil
s"
BUSHINQ
FiG, 44,
— Oscillators
hrasfi
rod
Foil
7 COIL
and Standards for
7"
Apparatus.
log
APPENDIX
For
those of our readers
disposal,
and who
who have
desire to carry
limited
Besides
many
this
who
possess an ordinary induction
three inch spark,
which they
may
This
coil
is
it
not
is
coil,
is
available,
giving a two or
article.
immersed, hence no boxes
oil
cities,
substitute for the trans-
former to be described in the present
required, as
Appendix
are not situated in
where an alternating-current lighting supply
but
at their
on some of the many experi-
ments possible with high-tension currents,
has been added.
means
will
be
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 reach
of
almost every one.
While speaking of
cost, let
us state
that to purchase a coil giving a 12" spark from the regular
dealers
coil in
tion
would mean an outlay
a single box
is
of about
The
worth S165.
by the amateur, not considering
exceed S50 for the 12" coil
and $25
$300, while the 7"
cost of construc-
his time,
should not
for the 7" coil.
This piece of apparatus giving about a
not exceed Sio to build at home.
It
is
3''
spark should
large
enough
for
most of the experiments on Roentgen and Geisler tubes and
for wireless
work
o\-er short distances.
The Tesla Coil
112
The above sums
include
simple
the
The
interrupter.
others will bring the price up in proportion.
The
high-frequency
coil is
made
Cut out two
as follows:
end pieces of i" wood lo" square and describe on each one
two concentric
having diameters of 9 and
circles,
On
respectively.
these circles bore a
come 36"
Y dowels.
mill
These are made of hard wood and
Cut each dowel
long.
inches
Next procure from a planing
apart as in the figure.
about twenty
number
7
of \" holes i"
into 12" lengths
and
fit
one
in each of the holes on the smaller circle of one of the boards.
When
they are
place the other board
all in
other end of the dowels.
The
empty
is
The
B.
& S.
until the
secondary
is
put on the
outer circle of holes
is
left
wound.
secondary winding consists of one layer of No. 32
gauge double cotton covered copper wire.
winding about
Y
from the ends.
Begin the
Shellac the wire with
several coats of the best orange shellac
when
the winding
is
finished.
The dowels
ing
for the
primary are next put in place by push-
them through the holes from one end.
tightly the holes
may be reamed
18 bare wire are
wound on
out.
coil is
six turns of
then mounted on a base.
Two
No.
oscillators
The ends
of
mounted on a
with standards are
provided for the terminals of the secondary.
pletes the high-tension coil.
too
it.
the primary are connected to two binding-posts
piece of hard rubber.
fit
the outer dowels, each turn being
over an inch from the one next to
The whole
Next
If they
This com-
A ppendix
^-
^--
1
"3
Tesla Coil
'^^'^
114
The condenser
lo" X 12", with a piece of tin
The method
of glass.
Lay a
follows:
While
top of
it,
8" x 10" between each sheet
foil
on a smooth
leaving an inch margin of glass
On
table
and
wet place a sheet of
still
corner lay a strip of tin
glass.
glass
of arranging this condenser
glass plate
coat of shellac.
window
consists of fifteen sheets of
it
On
a
on
tin foil
around.
all
as
is
gi\e
one
projecting an inch beyond the
foil
top of this lay a second sheet of glass and another
sheet of tin
only the strip in this case
foil,
on the opposite
Continue
side.
This
of glass are used up.
is
brought out
this until the fifteen sheets
will give seven sheets of tin
foil,
with the strips coming out on the one side and seven projecting
on the other
The
side.
strips
may
be fused together
with a hot iron and a copper wire soldered on.
condenser
best
is
mounted
The
bound together with
in
a box.
transformer for use with the
It
formers already described.
of
No. 20-22 iron
lY and when
II
in
is
wrapped with
The
after the
& S.
trans-
core consists of a bundle
The
method described
two sections one above the other.
Each
or 50-55 volt
same as the two
diameter
in
The primary
insulating tape.
of fastening the layers.
No. 16 B.
1 00-110
wires, well annealed.
formed
is
the next piece of apparatus
is
essentially the
is
and
This completes the condenser.
alternating-current circuits
to construjt.
The whole
insulating tape
See Fig.
i
is
Chapter
is
for the
wound
method
section consists of one layer of
gauge double cotton covered copper wire.
After the primary
is
wound wrap on
well shellacked until the diameter
is
several layers of paper
built
up
to 2}".
Appendix
"5
The Tesla Coil
ii6
The secondary winding
two
sections of
copper wire.
First
of
&
No. 32 B.
saw out
of wood, 4" in diameter
this
transformer consists of
gauge double cotton covered
S.
of \" stock four circular pieces
and having a
2 J" hole in the centre.
shown
Slip these on the primary to the positions
The two end
in the figure.
ones are |" from the ends of the core and the
middle ones are \" apart.
Wind
formed
layer
the wire of the secondary
until the
diameter
and wrap a piece
The whole
is
3J".
just
shellac each
on before beginning the
of paper
mounted on a
coil is
on the two spools
Thoroughly
next.
suitable base, the primary
terminals being connected to binding-posts.
If the
transformer
current, the
series.
If,
be operated on the loo-iio
to
is
volt
two sections of the primary are connected
on the other hand,
it
is
to
in
be u^ed on the 50-55
volt current the sections are joined in parallel.
It
is
well,
however, in either case to bring the primary terminals out
to
four separate binding-posts.
tions
may
Always be
be readily
certain,
the windings in the
In order
to set
made
Then
for
the desired connec-
either
series
or parallel.
though, that the current will traverse
same
direction.
up the high
oscillations
we must
introduce
a spark-gap in series with the secondary of the transformer
The method
and the high-tension
coil.
primary spark-gap
given as follows: Procure two pieces
is
of
making
this
of vulcanized fibre rod |" in diameter 4 inches long.
Drill'
a j" hole in each V' from one end.
holes
Next bore two
6" apart in the base of the transformer as
shown
-|"
in Fig. 47.
—
Appendix
117
Drive the fibre supports into these holes with the holes in the
fibre in line.
The spark-gap
fibre
tube
is
made
of
two }" brass rods 6" long with
long slipped over the end to act as an insu-
2''
One
lating handle.
lead of the secondary of the transformer
goes directiy to one rod, the other goes to the primary of the
high-tension
The
coil.
high-tension coil
is
return wire from the primary of the
soldered to the other side of the spark-gap.
The diagram shows how
the condenser
is
connected and also
the connections just described.
—6
^H
^--
1-
--^
i
Fig. 47.
There
care
is
Prim-^ry Spakk-g.\p.
no interrupter used with
must be taken that the spark
is
apparatus so that
this
long enough to prevent
arcing.
Those possessing a suitable induction
to substitute this for
may do
so
the transformer
coil
and who wish
and primarj' spark-gap
by changing one connection.
Disconnect one
terminal of the secondary from the discharger
the
and connect
secondary terminal to a binding-post suitably insulated
by hard rubber.
One
terminal of the primary of the high-
The Tesla Coil
ii8
tension coil
is
connected to the spark-gap instead of the sec-
ondary of the induction
tension coils primary
The
coil.
is
other terminal of the high-
connected to the new binding-post.
A glance at the figure will make this plain and also the method
Fig. 48.*-^
Fig. 49.
of connecting
WriUNG Diagram.
— Wiring
up the condenser.
Diagram.
When making
between the various parts of the apparatus
the wires in glass tubes
The
and
to
it is
connections
well to enclose
keep them back out of the way.
operator will soon find that ordinary insulation
is
of
Appendix
no value whatever
in dealing
so that all terminals
with these high-tension currents,
must be kept apart a distance greater
than that of the high-tenson discharge gap.
caution
is
119
If
this
pre-
not observed you will have some very beautiful
brush discharges
close proximity.
all
along the conductors that are in too