Re: An inexpensive X-ray machine

["Ed Phillips" <evp-at-xxxxxxxxxxx> (by way of Terry Fritz <twftesla-at-xxxxxxxxxx>)]

Tesla list wrote:
> 
> Original poster: "Chris Dobson" <cdobson-at-microtech-dot-com.au>
> 
> I think you'll find that a kick coil is simpler than an induction coil : its
> just a single coil on a soft iron core, with an interrupter assembly. The
> coil works by creating peaks of HV as the interrupter opens and the field
> collapses.
> ("The Amateur Scientist"  C.L.Stong, had full details for an Oudin coil
> outfit)

	The kick or kicker coil design is much more sophisticated and
interesting than that!  I can report three examples of the design of
such gadgets, and perhaps Antonio has something similar at his site.  

	First, the one in Stong's article.  It consists of a single 3800 turn
iron-core coil with an interruptor, with a 1 ufd capacitor bridging the
interruptor.  (Really, just an ordinary buzzer with a high-inductance
winding.)  This circuit is connected to the power line.  The capacitor
is connected in series with the 5 turn primary of an air-core
transformer, whose 3000 turn secondary output is the high voltage
desired. The principle of operation is simple:  current flows through
the iron-core coil until the interruptor opens the circuit.  At this
time the current from that coil continues flowing and charges the 1 ufd
capacitor.  When the interruptor closes again it shorts the series
circuit consisting of the 1 ufd capacitor and the primary of the HV
transformer, and the capacitor is discharged through the primary.  He
states that the capacitor can be charged to "several hundred volts", and
that the typical output voltage is of the order of 50,000 volts or so. 
Note that the HV transformer is air core and non resonant.

	The second example is in Curtis' "High Frequency Apparatus", Chapter
VIII, pp 86-99; a schematic diagram is given in Figures 35 and 36, page
87.  His "choke coil" (the one in series with the interruptor and the
line) has 1000 turns on a core of soft iron wires. The capacitor is
adjustable by taps up to a maximum capacitance of about 0.1 ufd, and the
number of turns on the secondary of the "oscillation transformer" is
hard to determine; it has a 10 turn primary made of 1" wide copper
ribbon.  His explanation of operation, in rather quaint pre-WW1
language, is:

	"Figure 35 represents a circuit of this nature.  The kicking coil K is
connected at one end of its winding with one side of the supply
circuit.  The other end of the winding goes to the vibrating armature of
an interruptor.  From the stationary contact of the interruptor we trace
this circuit of the primary of a Tesla or Oudin coil and thence back to
the source of the supply.  A condenser is connected across the break and
the primary of the oscillation transformer.
	As the current flowing through the coil is interrupted, a high
potential surge is set up.  This current enters the condenser which
discharges its load through the inductance and across the interruptor
contacts as soon as the latter close up sufficiently for the charge to
leap this small air gap.
	By making suitable adjustments of condenser and the ratio between the
turns in primary and secondary of the of the oscillation transformer, a
high frequency current of practically any desired frequency and voltage
may be obtained, within the limits of the outfit’s capacity."  

	It isn't clear whether the "oscillation transformer" is resonant or not
or at what frequency it oscillates, but from the mention of adjustment
of the capacitor it might be resonant.  His distinction between Tesla
and Oudin coils is the same one which has been repeater here several
times:  The Tesla coil has separate primary and secondary windings,
connect at the low-voltage end, while the Oudin coil is an auto
transformer.  Since the coupling is tight, suspect that there is no
difference in performance. 

	The third example I have is in my collection.  It was made by the
Rogers Electrical Manufacturing company, probably around 1915.  It
follows the same construction as the examples above, but is arranged
slightly differently mechanically.  The "kick coil", interruptor, and
capacitor are housed in a wooden box, while the "oscillation
transformer" is in a hard rubber tube about 1-1/2" diameter and 9" long,
at the end of an insulated cable.  The HV end of the oscillation
transformer is connected to a pointed electrode.  I'm not sure what the
thing was intended for, but it serves as an excellent leak-detector for
vacuum systems.  The maximum spark length is about 1 inch.

	Note that many "Tesla coils" have been sold for vacuum-system leak
detectors; I suspect they are still being sold.  The ones I have seen
are of single piece construction, with a line cord at one end and the
pointed HV terminal at the other.  One such unit is listed in a 1950
Cenco catalog I have.  I suspect all of these have the same basic design
as the ones I have described.

	In the early days of radio, so-called "buzzer transmitters" were used
for low-power work (up to perhaps 100 watts input).  They were of
similar design except that they were most certainly resonant at the
desired transmitting frequency.  Finally, the same principle was used
for RF signal generators.  A tunable series-resonant circuit was
connected across the contacts of a high-frequency buzzer.  When the
buzzer was energized a damped wave was generated at the resonant
frequency, and could be heard in a receiver.  

	I have a type 174B General Radio Wavemeter, built around 1922.  It can
operate either as a wave meter or signal generator.  The wave meter can
use either a hot-wire galvanometer or a crystal detector, while in the
signal generator mode the buzzer is engaged to operate as above.  The
tuning range is from 3000 meters (100 kHz) to 150 meters (2000 kHz), in
three ranges.  The whole thing is enclosed in a beautifully-made
mahogany case, about 9-1/2" by 7-1/2" square.  It works just fine in
either signal generator or wavemeter modes, and the frequency
calibration is within a couple of percent after nearly 80 years.  In the
signal generator mode it produces a signal which is easily heard on a BC
receiver, with a nice musical note.  I have looked at the output on a
spectrum analyzer, and the bandwidth of the signal leads me to believe
that the operating Q is around 30.

	Finally, I want to point out that exactly the same principle can be
used to excite the primary of a Tesla coil, in order to measure its
resonant frequency.  The buzzer is connected to a battery and the TC
primary circuit is connected across the contacts.  As the buzzer runs
the TC secondary is excited and the waveform can be observed on a
loosely-coupled oscilloscope, or heard on a suitable low-frequency
receiver.  I've tried this with a small (3" dia by 14" long) coil, and
it words fine.  I have a nice old buzzer which runs at about 400 Hz, so
the "tone" is fine and the waveform on the scope is nice and
repeatable.  I've been intending to write this up and post it here, but
this is the first time I have had the energy.  I think this very simple
low-powered technique might be of use to the community and would be
interested to hear from anyone who tries it.  Should work with coils of
ANY size!  No substitute for fancier techniques, but simple and quick.

Ed

Please forgive this long note.  It's been coming for about a year.