Lighting a tetrode thyratron

[pcravero]

Hello from a valve newbie.
At a hamfest I bought a Raytheon 2051 tetrode thyratron just because it looks nice and I am fascinated by old things that glow (nixies, VFDs, early LEDs).

The tube still contains some gas, since I can energize it with a neon tester. The filament is intact as well but does not produce visible glow since it is hidden into the structure.

I have seen videos of glowing thyratrons and I wonder if my sample could do the same with an average cathode current of 75 mA (and peak of 375 mA). Datasheet is attached.

Is this tube supposed to glow when conducting? Or the current is too low?

If it should glow, I would like to give it a try and I would appreciate directions towards a working circuit. I do build my own circuits but never tackled high voltage yet. I am aware of safety procedures when dealing with high voltage, though. All that I've gathered so far is that the filament needs to warm up for at least 10 seconds and that I would need to provide a load obviously with adequate power rating.

I will consider all your "wisdom transfer" (A.K.A. "input") as an opportunity to learn.

Thank you for reading,
Paolo

[Al (astral highway)]

Hey Paolo,

No data sheet attached?

I have a high power ex-Soviet thyratron in my collection , but I have no desire to operate it as there will be little to see. You can see what a thyratron does to 'the thing it controls', rather than how it conducts in itself.

They are really pulse devices , once the best way to to modulate high-powered radar magnetrons, although smaller ones appeared in time-bases in other equipment. My previous research on the subject found that most circuits illustrating them in use are rather more conceptual than literal, rarely with component values .

There was usually a pulse forming network using inductors and capacitors, and some arrangement for a strongly negative-going waveform at the grid to switch off the thyratron after each pulse, which would typically last uS. Because of the transient duration of the conduction cycle, (the sum of pulses amounting to milliseconds every second) you would be unlikely to detect any glow from the device, even if it were filled with a gas -typically hydrogen.

Thyratrons were prone to emit X-rays as the peak inverse voltage was often greater than 12,000V, hence they were replaced with safer modes of modulation. Mine is NOS from military manufacture in the 1980s, end of an era. Thyristors pretty much took over since.

[Radio Wrangler]

Hi Paolo,

I think those tubes are sought after by people with Seeburg Jukeboxes. I recall that they were used in the core-memory "Tormat" disc selection controllers.

David

[pcravero]

Hi.
I read about jukeboxe restoration projects (2051 is similar to 2050 and then more equivalent valves).

Datasheet is now attached. It is certainly lower power than Astral's!

I will keep on looking for a circuit then, with real/suggested values.

[julie_m]

Older Seeburgs use 2050 thyratrons in the read-out circuit of the Tormat Memory Unit, and also in the remote control stepper unit (which converts a stream of pulses from a remote wallbox to a pair of contact closures). My little one dates from 1973, though; all solid-state and no remote option.

Incidentally, the way Seeburgs work, they only keep track of selection credit centrally. If you insert a coin into a wallbox, someone can select a record at the console!

[Herald1360]

No skin off the operator's nose, there. He's got the money. The half cut user would probably just mutter and move on.......

[pcravero]

The attached picture shows the glow through the glass of my 2051 thyratron. The picture was taken in darkness, I apologise for the gainy effect.

A person on another list suggested that "Given enough current through the gas it will remain lit even after you disconnect the filament, until the gas cools sufficiently to prevent ionization."

I will give it a try once I locate a suitable resistor in my parts bins to act as a not-light-emitting load.

One possible problem though: the vapor inside the tube has deposited itself in the lower half of the glass as I cannot light the top as shown in the picture. I am now letting the tube rest upside down until I find the resistor, but I doubt it will have any effect on the short term.

Paolo

[Radio Wrangler]

They were designed as electrical switches, not as light emitters. For best switch performance the anodes enclosed as much as possible and little light gets out.

Some of the small mercury arc rectifiers are a bit more illuminated.

David

[Brigham]

The TUNGAR rectifiers used for charging accumulators in garages and cycle shops give a nice baleful light.

[G6Tanuki]

I'm wondering here if rather than feeding it with DC and getting it to do the ionisation-breakdown thing, it could be made to glow interestingly if powered from a high-voltage high-impedance RF source in the same style as the "violet glow" snake-oil medical devices used.

25KV at a microamp or three would be interesting to try.

[pcravero]

25 kV is way beyond my confidence level. My homebrew equipment usually stays under 10W input. Is there a modern circuit off-the-shelf that produces 25 kV/1uA?

The blue light you see in the picture was obtained with a HVAC field from a CCFL lamp driver (does the glass count as high impedance?). Is that the violet glow you are referring to, but induced with a uA current through the valve rather than through the glass?