25 July 2020

Independent glow from a Thyratron tube

Thyratron Glow!
This is a self follow-up of a 2017 experiment with a low-pressure gas-filled vacuum tube, a Raytheon Thyratron 2051. [Well, technically speaking this is not anymore a vacuum tube!]

While we know that the gas inside can be excited with an HVAC source through the glass, that seemed impractical when I wanted to show the lighted tube as if it was a (purple) bulb. So I set up a little test.

I fed the HVAC to the cathode. Touching the glass with my hand lights up the gas. Cool. No shock whatsoever.

Then I tried to close the HVAC circuit to the "cold" pole of the generator through a 10 Mohm resistor: now the gas lights up on its own. That's what I was looking for!

Replaced the resistor with 1 Mohm and there is a slight increase in brightness and, if the glass is touched, the glow spreads and increases.

Last improvement: heat up the filament/heater (I used 5.5 Vdc). This brings the glow to another level which is well noticeable in mid-darkness. The tube warms up too, good for the dark, cold Winter season.

I have seen glow forming at the top of the tube just once, probably while the filament was cooling down. I will experiment more to get a repeatable glow on the top too.

Apologies for the lousy picture. Too much light and you don't see the glow. Wrong white balance and the glow turns into blue (NO!). You need to get one of these if you want to see it, or wait that I set up a better photographic studio (evil grin ... this could lead to a challenge to a colleague who is into photography...)

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