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

But why when there are so many antiques available here to correct me

Maybe you are so cranky all the time because yous are really easy to manipulate into working for free.

I'm hearing that DLUNU would like to take responsibility for this project and I think he's the best qualified based on his rebuttal. I mean it's in his name. "NumeroUno"

bitrex 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.

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

bitrex 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.

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

Commonly called "Booth Boxes" or "Wall-Boxes" these used to be (and still are in a few places) jukebox remote controls that displayed a list of the songs available and a coin acceptor and push button system to make your remote selection on the in-house jukebox.

Not unlike a dial phone in many ways - used a pair of steppers - one for the letter (up to twenty) and a second for the number (up to ten) to make a selection of one of up to two hundred songs.

Some photos here:

John :-#)#

The off page connections are mostly switches. I'll find the wiring layout diagram and post it a bit later...

John :-#)#

From the service manual - the sequence of operations guide:

John :-#)#

Not unlike He-Ne laser tubes out-gassing He through the glass and failing back when LaserDisk players were somewhat popular (80s).

John :-#)#