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Re: [TCML] Thyratron

G Hunter wrote:
The recent trigitron coil question has got me
wondering:  Has anyone ever built, seen, or even heard
about a successful disruptive tesla coil using a
thyratron tube or tubes in place of the spark gap?  If
so, kindly share what you know.  A link will be most

Happy New Year,


Hi Greg,

As you may recall (if you were on the TCML at that time), Richard Hull of the TCBOR made a thyratron-driven coil. Unfortunately it "fired" only for one half of an RF cycle and then quenched (at the very first current zero). It also used a comparatively low power H2 thyratron - the 3C45 (3 kV, 35A peak). When triggered, it conducted for one-half cycle, but when the voltage across the tube began to reverse, the tube went into cutoff, blocking any further current flow. Because "ring-up" was prematurely aborted, very little primary energy was actually transfered to the secondary. You can likely find information in the TCML archives circa 1997 - search on "thyratron".

BTW, Richard Hull performed some very interesting experiments with this particular coil that seemed to demonstrate that disruptive Tesla Coils generated a DC electrostatic field around them. Subsequent research determined that this effect was an instrumentation artifact:

There is at least one other Tesla Coil that uses a hydrogen thyratron switch - a somewhat larger EEV 8503/CV6022 (16 kV, 325A peak - similar to a 5C22, but ruggedized). This system, while larger, suffers from the same premature quenching problem as Richard's earlier coil. However, by using tighter coupling, a bit more energy can be transfered to the secondary during the single primary pulse. The circuit operates like a bell (the secondary) being struck by a hammer (a single pulse). Although the site is in German, you can use Google language tools to help translate it to English, and it contains a schematic:

In order to avoid the premature quenching problems seen in the above systems, one could use an anti-parallel HV diode across the thyratron to conduct in the reverse direction. Other options include an anti-parallel hydrogen diode (a scarce device, similar to a hydrogen thyratron, but with no accessible control grid), or a similar H2 thyratron connected in anti-parallel. One would also need to provide a series of properly phased trigger pulses to turn on the thyratron(s) on every appropriate half cycle until ring-up (energy transfer from primary to secondary) had completed.

It may also be possible to use a specially constructed "Hollow anode" thyratron that can safely conduct in the reverse direction. Normally, reverse conduction causes arcing that destroys cathode material. These devices are often used as switches in excimer laser systems. Since reverse current is usually limited to 50% of the previous forward current, their use in a high Q Tesla Coil primary circuit may be limited. The relatively high cost of hydrogen or deuterium thyratrons and associated circuit complexity have most likely been the reasons why thyratrons have not been actively pursued.

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