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1932 article on singing arc
-
From: William Noble[SMTP:William_B_Noble-at-msn-dot-com]
Sent: Friday, June 20, 1997 8:47 PM
To: Tesla List
Subject: 1932 article on singing arc
Norman stanley sent me a photocopy of subject article, but I don't have an E
mail address to return the OCR'd file to - so I am posting the text portion of
the document here. I have the whole document as a word 97 file, so if you
want it with the pictures, drop me a note and I'll send it out.
=========================================
Experiments with "Singing
and Tesla Coil
By W. MOELLER (Germany)
SINCE radio discovery y began the methods used to generate high fre- have
often changed. There was first Hertz's resonant circuit excited by sparks;
this method, while applicable to telegraphy creates only damped waves
unsuitable for modulation In 1900 while seeking a method of created undamped
waves, Duddell\ discovered the "singing arc" he demonstrated that an arc
light is capable of exciting continuous oscillation in a parallel resonant
circuit. In 1906 Valdemar Poulsen constructed the first practical arc
transmitter for transmissionwork; but it was soon superseded by the
vacuum-tube transmitter.
However, students of radio development will find experiments with the
arc-light generator quite interesting; and they can be performed with com-
simple means, such as a small laboratory affords The first is Duddell's
classic experiment, showing the generation of alternating current in any
circuit containing capacity and inductance as soon as it is connected across
an electric arc
An apparatus like that illustrated in the center, below and corresponding to
the schematic circuit of Fig. 1, i:; set up. The direct-current supply should
be about 200 volts. The current flows through the regulating resistance R and
through the audio choke L1 to the carbons; returning through the ammeter A and
the second audio choke L2. The chokes and resistor should be cap- of passing
the necessary current without becoming too hot. The carbons are a quarter of
an inch thick, or so.
The part of the circuit at the right -- including the condenser C and coil L,
with the hot-wire ammeter HA- is switched in later The capacity of C is.; 4
mf. and its rating should be at least 700-volt D.C. test; the coil L is 2
inches in diameter and has 60 turns of No. 18 wire, suitably insulated. (The
frequency of this tuned circuit falls within the audible range.)
The experiment begins by bringing the two carbons in contact and separating
them a small fraction of an inch; thus starting the arc. The resistor, R, is
set to give a suitable current flow; as much as 2 amperes may be l readily
drawn from the light-lines.
If w e now switch in the resonant ciruit C-L, the arc gives out a whistling
note. At the same time, we see, the hot- e ammeter HA gives a kick. Since
this circuit is blocked to direct current, by the blocking condenser, C, it
is evident that the cause must he a flow of alternating em rent. Therefore we
know that the circuit is oscillating, and the current in it is relatively
great; in the writer's experiments it has amounted to 4 amperes, registered by
the hot-wire ammeter.
Why the Arc "Sings"
The cause of the sound deserves explanation. When the resonant circuit is
shocked into oscillation, alternating current ale set up, and flow over the
leads into the carbons; they cannot pass out into the feed-lines, because the
chokes L1 and L2 stop their flow. Consequently, the alternating current is
superimposed on the direct current in the carbons, e causing alternate
strengthening and weakening. This also causes a fluctuation in the emission
of ionized gas from the arc; and the temperature of the air about it
fluctuates also, setting up successive compressions and rarefactions, which we
term "sound waves", and which our ears recognize.
The small Tesla coil used by the author, with its coronal discharge from the
high-voltage end: the large primary is for connection to a high-voltage
generator.
At the top, the fundamental circuit of the arc-light generator, which came
before the vacuum tube. Below. Various experiments with the circuit.
The layout Of the equipment used in these high-voltage. high-frequency
experiments The condenser and coil determine the tuning of the circuit in
which the arc sets up oscillations At the right, experiments in the field of
the coil, and method of keeping arc in atmosphere of hydrocarbons.
Our second experiment is to vary the capacity of the condenser C; if it is
replaced by one of 2-MF., the note becomes higher, with an increase in the
frequency of the oscillating circuit. We may, as In Fig. 2A, substitute a
group of condensers, 50 that we can switch from one to another; the pitch will
change.
5imilarly. as in Fig. 2B, we may substitute coils with d referent numbers of
turns: the altered inductance also affecting the pitch o! the note emitted by
the arc. More inductance (that is, more turns. on the same diameter with same
spacing) the deeper the note,
If we substitute for the 4-mf. condenser with which we started, a radio tuning
condenser, with a value of .0005-mf., for instance, there is no oscillation in
the radio-frequency resonating circuit thus produced, Not only will there be
no audible note, but the hot-wire ammeter will register no current. We will
deal smith this phenomenon further on.
HIGH-FREQUENCY TEST
All alternating currents have the property of causing magnetic coupling
between circuits. If we make two turns of heavier copper wire, say No. 12, two
inches in diameter., and connect the ends across a small flashlight bulb, as
its detail A, attach an insulating handle; and approach the resonating coil L.
with the exploring coil held parallel to the windings of L, we shall find that
the lamp lights up brilliantly.
We can also increase the inductance of the coil L by introducing into its
center a piece of iron rod. as shown in detail B. This ``ill at once produce a
decided change in the pitch of the tone emitted by the arc.
Alternating currents produce, by induction, local currents in metal masses of
any shape or form. The presence of these "eddy currents" may be demonstrated
by putting a few small nails or screws in a test tube. covering them with
water, and introducing the tube into the field of the coil L (Detail C). Not
only will this have its effect on the tone of the arc: but after a few minutes
we shall find the glass warmed by the heat generated by the eddy currents ire
the metal, anal transmitted by the water, (This is the principle of the
high-frequency furnace.)
REACHING RADIO FREQUENCIES
As said before. we failed to generate ratio frequency current by the coil when
we reduced the capacity of the condenser to a proper value. Even a, .0001-mf.,
the writer failed to obtain a reading on the hot-wire ammeter.
However, we can easily obtain a positive result here; we have only to let the
carbons burn in an atmosphere of hydrocarbons. This is easily obtained by
placing tinder the arc a Bunsen burner, with the air holes at its base closed.
If we now replace the big condensers by a variable condenser, of .0005-mf., or
ogle of the older 001-mf. instruments, then our hot-wire ammeter at once
registers. Also, our exploring coil will show that high-frequency current is
being generated in the oscillating circuit. There is. however. no whistle from
the are: eve are in the range of radio-frequency vibrations, above the audio
range. We have, in fact, a miniature "arc transmitter".
The resonance of radio circuits. similarly tuned. is at the basis of radio
transmission and reception. We can illustrate the principle. as in Fig. 3. by
setting up a similar oscillating circuit with a coil. LE, wound like L, and
with a similar variable condenser across its ends in series with a small neon
lamp. When the circuits are tuners alike. the bulb lights up. It makes no
difference whether eve tune the receiver to the transmitter, or the
transmitter to the receive en
If we take the receiving circuit further away, we thus reduce the coupling.
and increase the sharpness of response. If we come closer, the sharpness is
reduced, but the current received is much greater.
We may place the test coil some distance away, at right angles to the
oscillating coil L, and make a direct coupling with a piece of wire, as in
Fig. 4: the lamp will light. The effect of tinning may be again demonstrated.
Of a condenser, to introduce capacity. The distributed capacity of a winding
may serve, as in the well-known Tesla coils.
For these experiments, it is easy to make a Tesla coil. by winding on any
suitable insulating tube, 14 inches long, anti 11/4 inches in diameter. a full
layer of No. 32 D.S.C. wire. This is close wound, and the spool is covered
with a suitable lacquer, or collodion. to hold the windings in place.
The beginning of the winding is grounded. through a binding-post attached to
its base: and the other end iri connected to a brass ball, at the top of the
tube-.15 illustrated in the photograph reproduced at the head of this article.
The base holds the coil upright.
Such a coil has considerable self-capaciry. between its respective windings,
one with another. which reaches a very respectable total. This capacity makes
it possible for the whole coil to have a natural fundamental frequency. In
response to excitation. this is capable of oscillating: as we shall proceed to
demonstrate by coupling it to the arc generator.
The arc has been introduced into an atmosphere of gas (Detail D) as explained
above The capacity C is now represented by a .001-mf. Variable condenser: whim
the coil L has now been replaced by five turns of No. 12 heavy bare copper
wire. 8 inches in diameter, and almost self-supporting.
The Tesla coil is placed in the center. as shown in our first illustration,
with its "foot" grounded.
The current through the Tesla coil will he too small to light a filament-type
incandescent lamp; but the alternating voltage at the terminal of the coil is
very high, and we can utilize this fact to light a neon lamp-one of those. for
instance, used to test a radio receiver. We apply the test prod of such a neon
lamp to the ball at the top of our Tesla coil.
A, soon as the oscillating circuit of our arc-generator is tuned to the
fundamental frequency or the Tesla coil, the lamp applied to the top of the
latter will light brilliantly with the rushes of current back and forth, into
and front this capacity (Fig. 5).
We may also. if we wish. test direct. Instead of inductive, coupling to the
Tesla coil. as we did before with our external tuned (receiving) circuit. This
is shown in fig. 6, where the coil L is common to both the Tesla coil's
circuit and that of the arc-generator circuit. Grounding is effected now
through a 1-mf. fixed condenser C. As before, the neon lamp will light up, to
denote the oscillating condition in the Tesla coil.
The test lamp lights, proving that the Tesla coil is oscillating at high
frequency,
666 EVERYDAY SCIENCE AND MECHANICS for JUNE, 1932
Experiments with "Singing
and Tesla Coil
By W. MOELLER (Germany)
SINCE radio discovery y began the methods used to generate high fre- have often changed. There was first Hertz's resonant circuit excited by sparks; this method, while applicable to telegraphy creates only damped waves unsuitable for modulation In 1900 while seeking a method of created undamped waves, Duddell\ discovered the "singing arc" he demonstrated that an arc light is capable of exciting continuous oscillation in a parallel resonant circuit. In 1906 Valdemar Poulsen constructed the first practical arc transmitter for transmissionwork; but it was soon superseded by the vacuum-tube transmitter.
However, students of radio development will find experiments with the arc-light generator quite interesting; and they can be performed with com- simple means, such as a small laboratory affords The first is Duddell's classic experiment, showing the generation of alternating current in any circuit containing capacity and inductance as soon as it is connected across an electric arc
An apparatus like that illustrated in the center, below and corresponding to the schematic circuit of Fig. 1, i:; set up. The direct-current supply should be about 200 volts. The current flows through the regulating resistance R and through the audio choke L1 to the carbons; returning through the ammeter A and the second audio choke L2. The chokes and resistor should be cap- of passing the necessary current without becoming too hot. The carbons are a quarter of an inch thick, or so.
The part of the circuit at the right -- including the condenser C and coil L, with the hot-wire ammeter HA- is switched in later The capacity of C is.; 4 mf. and its rating should be at least 700-volt D.C. test; the coil L is 2 inches in diameter and has 60 turns of No. 18 wire, suitably insulated. (The frequency of this tuned circuit falls within the audible range.)
The experiment begins by bringing the two carbons in contact and separating them a small fraction of an inch; thus starting the arc. The resistor, R, is set to give a suitable current flow; as much as 2 amperes may be l readily drawn from the light-lines.
If w e now switch in the resonant ciruit C-L, the arc gives out a whistling note. At the same time, we see, the hot- e ammeter HA gives a kick. Since this circuit is blocked to direct current, by the blocking condenser, C, it is evident that the cause must he a flow of alternating em rent. Therefore we know that the circuit is oscillating, and the current in it is relatively great; in the writer's experiments it has amounted to 4 amperes, registered by the hot-wire ammeter.
Why the Arc "Sings"
The cause of the sound deserves explanation. When the resonant circuit is shocked into oscillation, alternating current ale set up, and flow over the leads into the carbons; they cannot pass out into the feed-lines, because the chokes L1 and L2 stop their flow. Consequently, the alternating current is superimposed on the direct current in the carbons, e causing alternate strengthening and weakening. This also causes a fluctuation in the emission of ionized gas from the arc; and the temperature of the air about it fluctuates also, setting up successive compressions and rarefactions, which we term "sound waves", and which our ears recognize.
The small Tesla coil used by the author, with its coronal discharge from the high-voltage end: the large primary is for connection to a high-voltage generator.
At the top, the fundamental circuit of the arc-light generator, which came before the vacuum tube. Below. Various experiments with the circuit.
The layout Of the equipment used in these high-voltage. high-frequency experiments The condenser and coil determine the tuning of the circuit in which the arc sets up oscillations At the right, experiments in the field of the coil, and method of keeping arc in atmosphere of hydrocarbons.
Our second experiment is to vary the capacity of the condenser C; if it is replaced by one of 2-MF., the note becomes higher, with an increase in the frequency of the oscillating circuit. We may, as In Fig. 2A, substitute a group of condensers, 50 that we can switch from one to another; the pitch will change.
5imilarly. as in Fig. 2B, we may substitute coils with d referent numbers of turns: the altered inductance also affecting the pitch o! the note emitted by the arc. More inductance (that is, more turns. on the same diameter with same spacing) the deeper the note,
If we substitute for the 4-mf. condenser with which we started, a radio tuning condenser, with a value of .0005-mf., for instance, there is no oscillation in the radio-frequency resonating circuit thus produced, Not only will there be no audible note, but the hot-wire ammeter will register no current. We will deal smith this phenomenon further on.
HIGH-FREQUENCY TEST
All alternating currents have the property of causing magnetic coupling between circuits. If we make two turns of heavier copper wire, say No. 12, two inches in diameter., and connect the ends across a small flashlight bulb, as its detail A, attach an insulating handle; and approach the resonating coil L. with the exploring coil held parallel to the windings of L, we shall find that the lamp lights up brilliantly.
We can also increase the inductance of the coil L by introducing into its center a piece of iron rod. as shown in detail B. This ``ill at once produce a decided change in the pitch of the tone emitted by the arc.
Alternating currents produce, by induction, local currents in metal masses of any shape or form. The presence of these "eddy currents" may be demonstrated by putting a few small nails or screws in a test tube. covering them with water, and introducing the tube into the field of the coil L (Detail C). Not only will this have its effect on the tone of the arc: but after a few minutes we shall find the glass warmed by the heat generated by the eddy currents ire the metal, anal transmitted by the water, (This is the principle of the high-frequency furnace.)
REACHING RADIO FREQUENCIES
As said before. we failed to generate ratio frequency current by the coil when we reduced the capacity of the condenser to a proper value. Even a, .0001-mf., the writer failed to obtain a reading on the hot-wire ammeter.
However, we can easily obtain a positive result here; we have only to let the carbons burn in an atmosphere of hydrocarbons. This is easily obtained by placing tinder the arc a Bunsen burner, with the air holes at its base closed.
If we now replace the big condensers by a variable condenser, of .0005-mf., or ogle of the older 001-mf. instruments, then our hot-wire ammeter at once registers. Also, our exploring coil will show that high-frequency current is being generated in the oscillating circuit. There is. however. no whistle from the are: eve are in the range of radio-frequency vibrations, above the audio range. We have, in fact, a miniature "arc transmitter".
The resonance of radio circuits. similarly tuned. is at the basis of radio transmission and reception. We can illustrate the principle. as in Fig. 3. by setting up a similar oscillating circuit with a coil. LE, wound like L, and with a similar variable condenser across its ends in series with a small neon lamp. When the circuits are tuners alike. the bulb lights up. It makes no difference whether eve tune the receiver to the transmitter, or the transmitter to the receive en
If we take the receiving circuit further away, we thus reduce the coupling. and increase the sharpness of response. If we come closer, the sharpness is reduced, but the current received is much greater.
We may place the test coil some distance away, at right angles to the oscillating coil L, and make a direct coupling with a piece of wire, as in Fig. 4: the lamp will light. The effect of tinning may be again demonstrated.
Of a condenser, to introduce capacity. The distributed capacity of a winding may serve, as in the well-known Tesla coils.
For these experiments, it is easy to make a Tesla coil. by winding on any suitable insulating tube, 14 inches long, anti 11/4 inches in diameter. a full layer of No. 32 D.S.C. wire. This is close wound, and the spool is covered with a suitable lacquer, or collodion. to hold the windings in place.
The beginning of the winding is grounded. through a binding-post attached to its base: and the other end iri connected to a brass ball, at the top of the tube-.15 illustrated in the photograph reproduced at the head of this article. The base holds the coil upright.
Such a coil has considerable self-capaciry. between its respective windings, one with another. which reaches a very respectable total. This capacity makes it possible for the whole coil to have a natural fundamental frequency. In response to excitation. this is capable of oscillating: as we shall proceed to demonstrate by coupling it to the arc generator.
The arc has been introduced into an atmosphere of gas (Detail D) as explained above The capacity C is now represented by a .001-mf. Variable condenser: whim the coil L has now been replaced by five turns of No. 12 heavy bare copper wire. 8 inches in diameter, and almost self-supporting.
The Tesla coil is placed in the center. as shown in our first illustration, with its "foot" grounded.
The current through the Tesla coil will he too small to light a filament-type incandescent lamp; but the alternating voltage at the terminal of the coil is very high, and we can utilize this fact to light a neon lamp-one of those. for instance, used to test a radio receiver. We apply the test prod of such a neon lamp to the ball at the top of our Tesla coil.
A, soon as the oscillating circuit of our arc-generator is tuned to the fundamental frequency or the Tesla coil, the lamp applied to the top of the latter will light brilliantly with the rushes of current back and forth, into and front this capacity (Fig. 5).
We may also. if we wish. test direct. Instead of inductive, coupling to the Tesla coil. as we did before with our external tuned (receiving) circuit. This is shown in fig. 6, where the coil L is common to both the Tesla coil's circuit and that of the arc-generator circuit. Grounding is effected now through a 1-mf. fixed condenser C. As before, the neon lamp will light up, to denote the oscillating condition in the Tesla coil.
The test lamp lights, proving that the Tesla coil is oscillating at high frequency,
666 EVERYDAY SCIENCE AND MECHANICS for JUNE, 1932