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

What happens to them as they age? is that with respect to the unused NOS types?

I was under the impression that small-signal gas thyratrons were very reliable in service. They're much less temperature sensitive in service than solid state devices, at least. If you blast a relaxation oscillator made with a 2D21 with cold spray it barely drifts.

I may have a few of either floating about in my junk boxes. If so, I would be glad to send all that I have to you as I have no discernable use for them. I seem to remember those numbers,

Gratis, of course. I will let you know.

Peter Wieck Melrose Park, PA

The 2D21 tubes become erratic, sometimes they respond, sometimes they are slow (the solenoid grumbles as it sluggishly engages), and sometimes they just ignore the control signal. Yet these tubes test OK on my mutual conductance tube checker (of course).

John :-#)#

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Maybe the hydrogen is out-gassing thru the glass over time?

The tube tester can test for conductance from thermionic emission but IDK if it can test for the conductance when the tube is operating in the ionization-cascade mode.

Got a schematic? It might be easy.

A tube tester may not apply enough voltage or current capability to fire the gas, so would miss a problem with ionization.

What's the Gm of a thyratron anyhow?

One could build a simple thyratron tester.

The 1954 gear was probably designed to run on old-timey line voltage of ~110 AC. Dialing back the heater voltage on the thyratrons to compensate for higher modern AC supply voltage might extend their life.

Hydrogen diffusion through thin glass within tube-like operating temperatures, where the gas is in thermal equilibrium with the glass and the mean free path is >> glass thickness is dominated by e^(-1/T), so if hydrogen outgassing is causing the erratic behavior whether the tube envelope temperature is run before the "knee" or after may have a lot to do with the expected service life.

I may have the pac-mans backwards there don't quote me on that. :)

Thyratron anode conductance is grid current-controlled when in the ionization mode, you can read off the parameters from fig 2 of the 2D21 datasheet. For grid 1 voltages between about -1 and -5 volts and Ib between 25 and 200 mA it's vaguely linear at about 50mA per 1 mA.

A fairly recent scan (not tidied up) of my files section for the V200 Control Center:

Relevant schematic is on page 5128 (pg 16 or the PDF).

The first control center is the original TSR1-L6, later it shows the replacement control center the TSR3-L6.

You can ignore the stepper section, that is the interface to allow booth boxes (called Wall Boxes in the industry) - but it doesn't matter unless one is using those remote selectors...

Thanks for looking at this!

John :-#)#

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This controlled a solenoid at around 24VAC or regulated (0A2 = -150VDC) power supply for the tormat write-in and readout circuits.

John :-#)#

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                      John's Jukes Ltd. 
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 
          (604)872-5757 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."

Designing a workaround would be easier from the standpoint of seeing exactly how it's wired in a circuit as opposed to making a general sub for that tube. Is there a schematic on-line anywhere?

A thyratron is similar to an SCR, maybe a sensitive-gate type like

2N5064 could be made to work. This one is apparently Xenon-filled.

I don't have the relationships of the thyratron grids in my head though, never designed with one (I once fixed a spot welder that had an enormous lethal-looking high voltage thyratron tube (cap on the top) and a giant step-down transformer to give the kA pulse). Hardly touched vacuum tubes after HS, for that matter.

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Spehro Pefhany

Between the forces of good and the Evil Empire they must have made bajillions of these things. Why OP not buy a gross from Russia? Just sitting in their boxes in a dry environment the shelf life might be measured in centuries.

Where's the fun in that? As I said, I know I can still get new tubes. The problem is the system doesn't work well...

John ;-#)#

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(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 
          (604)872-5757 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."

I had a look at the pdf and the schematic looks like a typical work of art from that era.

So you could probably get a solid state equivalent designed if you wanted to pay a designer with the necessary experience to do it. I'm not offering but I'd need the hardware in the same room as me to have any chance.

bitrex wrote in news:X0_fI.33919$ snipped-for-privacy@fx41.iad:

110 VAC went away at the beginning of the 20th century. By 1950 120 Volts was the standard. The MONIKER remained, but the voltage has been 120 VAC for a VERY long time.

The line voltage was already 120 Volts by then. You need a remedial electrical system / electronics industry history course.

Or maybe you would simply develop enough Internet skills to know how to use google properly.