Re: Still more H2 Thyratron


Hydrogen thyratrons are used for high voltage, moderate current
switching, where the average current levels are comparatively low. When
combined with a DC charging source and HV pulse forming network, they
can be used to provide pulsed power for high-energy experiments or for
pulsed RF (RADAR, partical acellerators). A thyratron is the vacuum tube
analog to a Silicon Controlled Rectifier (SCR) - once turned on, current
flow through the device must be stopped or the applied voltage reversed
in order to turn off the device. A thyratron is triggered by a positive
pulse on the control grid, which is normally biased to a negative DC
potential versus the cathode. Once the thyratron begins to conduct, the
grid no longer has any control over the device. Except for speciallized
pulsed-power applications, thyratrons have pretty much been displaced by
SCR's, MOSFET's and IGBT power devices, so finding information on them
can be a bit difficult. Unfortunately, most thyratons are unipolar
devices which can only safely conduct current in one direction once
triggered. This tends to limit the usefulness of a single-thyratron
switch where bidirectional current flow is required, such as replacement
for a spark-gap in a medium power Tesla Coil.

Regarding what coilers are doing with these - many do experimental
research with other high voltage devices, and I suspect that many of
these thyratrons are actually targeted for experimental home-brew pulsed
lasers. There has also been some research (most notably by Richard Hull)
on applying thyratrons to a small research Tesla Coil by means of a HV
DC power source and triggered thyratron. In this case, only a single
half-sinusoidal current pulse from a charged capacitor drove the TC
primary. A number of coilers (myself included) may now want to extend
this technique to make a bipolar equivalent to a spark gap.

Getting high power hydrogen thyratrons at affordable prices can be more
difficult than getting affordable pulse caps! Hydrogen thyratrons are
much preferred over the more common mercury vapor or xenon type because
of the smaller amount of time required for the device to recover (turn
"off") once forward current flow has been stopped. I was fortunate
enought to obtain a couple of high-power [40 kV, 15 kA peak] ceramic
thyratrons which were originally out of a pulsed laser system. I'm
looking to use them in a back-to-back configuration to make a
bidirectional 20 kV switch in a TC tank circuit. By controlling when the
thyratons fire, and the duration of the triggering signals, the idea is
to make a variable-rate, variably-quenching spark gap for a medium
powered DC system. The control ciruitry and concepts would be proved-in
by first using a pair of lower power 5C22's. Hydrogen thyratons are NOT
as efficient as regular spark gaps - this system would be more focused
on research, not efficiency. However, a "programmable" spark gap would
permit easy adjustment of pulse rate (up to 1000 PPS) and quenching
control that would otherwise be unobtainable. 

Pin-out and technical data for the 5C22 (and many other vacuum-tubes)
can be found on Kristian Ukkonen's funet site:

The 5C22 takes a Jumbo 4-pin socket (Eimac SK211 or E. F. Johnson
123-211), and the anode cap is the same as that for an 811A (or if you
want to go fancy, a finned cap shuch as the HR8). These are often
readily available on e-bay, at RF Parts at 1-800-737-2787 or
http://www.rfparts-dot-com/  or from Surplus Sales of Nebraska at
1-800-244-4567/402-346-4750 at: http://www.surplussales-dot-com/

The trickiest part is finding applications information for thyratrons in
order to use them without damaging them. It's important that the tubes
be given enough time to warm up (typically 10 minutes), and that no
large reverse currents (due to breakdown) be permitted, since these may
irreversably damage the cathode. Most information consists of either low
frequency power-control for motors or incandescent lamps (pre-SCR era),
or RADAR modulator applications. And most of these sources are out of
print, but many are available on the used book market or available from
engineering libraries at some of the larger schools. Some books to look
for include:

1. Glasoe, G. N. & J. V. Lebacqz, "Pulse Generators", McGraw-Hill, 1948,
741pp (this book has been reprinted several times by Dover, Boston
Technical Publications, and McGraw-Hill). Great book to have for spark
gaps as well!

2. Reich, Herbert J., "Theory and Applications of Electron Tubes", 2nd
ed., McGraw-Hill, 1944, 716pp 

3. Henney, Kieth, "Electron Tubes in Industry", 2nd ed., McGraw-Hill,
1937, 539pp (has a large gaseous tride/thyratron section)

Hope this helped, and good luck on your quest!

-- Bert --

Tesla List wrote:
> Original Poster: "Joel Hinchman" <joel-at-molalla-dot-net>
>         I've got to ask, what are all the coilers using H2 Thyratron
devices for?
> Originally my application was for a high-speed charge transfer switch, I've
> read that these tubes are real performers but am still not entirely positive
> on how to use them.  The Thyratron device is favored over any silicon
> devices due mainly to their abilities to withstand high-voltages (silicon
> devices are generally limited to about 1,000V) and the short pulse duration
> possible.
>  I just picked up a set of 5C22 (Sylvania in this case), still looking for
> pin-out and example schematics.
> Joel H.