A solid state replacement for the lowly 2D21 Thyratron tube...(sorry for the On-Topic post!)

bitrex snipped-for-privacy@example.net wrote in news:O36gI.7688$ snipped-for-privacy@fx09.iad:

In case you missed it, he was backing me up.

I would hope so! You're team lead, now

There's this patent from '66 that describes a solid-state thyratron replacement:

It uses a couple of SCRs. It's to replace high-power thyratrons but I don't see why it couldn't be scaled-down.

What's a "Wall-o-Matic"?

I can't find a solid reference on what the gas in the 2D21 is, anyway. Only few references from the time period I can find don't agree, one paper says it's hydrogen:

Another says it's xenon:

Maybe a mixture of stuff.

Sounds like this might be a good application for a Silicon Carbide FET ?

I think it must be xenon, the first one is just wrong

bitrex snipped-for-privacy@example.net wrote in news:mh6gI.266012$ snipped-for-privacy@fx42.iad:

No... According to the LarkinPunk, I am a mere "technician" who "hates the magic" of engineers.

Thanks Bitrex, that patent even mentions a tunnel diode and UJT which are now very exotic devices. The struggle was to emulate the high impedance thyratron grid. It seems to me (I have never seen a thyratron) that a modern depletion mode mosfet would make a good front-end to a SCR in that a negative grid bias is required to keep the device non-conducting (if I understand thyratrons correctly).

Here is a conceptual sketch:

Possible fets could be BSS126 or LND150 and SCR with sensitive gates X0402NF or BT149G.

piglet

Well Fig 2 in the patent doesn't look like it requires anything exotic, the exotics look to be included in the "further embodiment of the invention"

Yeah, depletion mode MOSFET seems a plausible modern take on it. Only thing is a real gas thyratron the anode current is controlled by the control grid current when it's in the low impedance ionized state. In many switching applications though I expect this doesn't matter too much it doesn't matter what the impedance is in that state exactly, just so long as it's low enough to reliably fire the relay or whatever.

And there doesn't need to be an analog to the screen grid, when the tube is used like a switch to ground it's usually connected to the cathode and just prevents the thyratron from firing until the positive-going pulse on the control grid is seen. You can see in a 2D21 a box-like structure surrounding all the other electrodes and I believe that whole structure is connected to the screen grid pin.

Sounds like you have something to prove. Sometimes when I'm helping the little ol' lady in the library do her taxes some kid shows up with something to prove too and is like "No dummy you're doing that all wrong" and then I say "Okay.." and hand the job off directly to him, let him spend the next two hours with her while I go about my day. I'm not going to fight him on it he is the white-knight expert who has appeared in our time of most need. And it makes Ethel very happy!

But that's interesting about the line voltage it seems to be a common misconception and 1954 was a long time before I was born. In any case my thoughts on the 2D21-dying issue have changed it's not hydrogen-filled it's probably primarily xenon. Hydrogen-filled thyratrons are more temperature-sensitive to both the temperature of the heater and temperature of the glass if they're too hot all the hydrogen tries to run away or react with the hot cathode. Obviously xenon won't react with the internal elements or the getter but it can still be absorbed by the glass or escape where the pins come in.

So I still think the reason they end up malfunctioning in service is that the gas is escaping or being absorbed by the glass and reducing the operating temperature of the cathode may extend their life.

Oh okay I see what you're saying, instead of using a high-impedance SCR as the first element in a two-SCR pair there are better devices to solve that "struggle" of the inventor, now.

Unless the tube was also expected to emit light, hydrogen was almost universally used in thyratrons.

One can probably tell from the grid voltage needed to cause the tube to trigger, as the ionization voltages of the various kinds of gases differ. A complication factor is if there is a bit of radioactive material in the tube to stabilize triggering.

Thyratrons are the kid brother of mercury-pool ignatrons.

Joe Gwinn

I noticed after-the-fact the datasheet says "Inert-Gas Thyratron" but what an "inert gas" in this context is exactly IDK the term is somewhat ill-defined. Does it mean a noble gas where all the valence electron energy levels are filled? Or is like nitrogen considered an "inert gas." Hydrogen does seem like it's an "inert gas" to me.

The ionization potential of hydrogen and xenon isn't too much different, xenon is lower by like 1 eV:

I don't think the experiment in the second paper previously would work if there were no xenon in the thing. It may be a mixture of gases.

This other paper I was looking at from the 40s said the internal elements of a pure hydrogen thyratron had to be made very pure and non-reactive, like 99.5% pure nickel or something to prevent the hydrogen reacting with it, and the cathode temperature very tightly-controlled to prevent the hydrogen reacting with the barium oxides. Sounds expensive. The 2D21 was cheap jonk

All gaseous elemental hydrogen wants to do is react or go bye-bye to space

Doesn't seem like it's an inert gas, rather

I don't think they put no radioactive material in that thing, not needed it doesn't need to fire that fast. Also sounds expensive

Yikes. The tube pins all go to off-page connectors, so it's not easy.

And krytrons.