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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Compactron VR tubes

Is there such a thing? Been looking for a couple of days but couldn't find anything. I'm putting together a compactron amp, and would like to keep it all the same type of tubes if possible. I looked for coin based VR tubes but also struck out. I have 0D3 tubes in a GT envelope which kind of fit the aesthetics, but there's the black plastic base. I suppose I can try to swap the regular octal base for a coin base, but I'm not sure if I want to do that. Thanks in advance.
Are you trying to regulate screen voltage for an amplifier?

Bingo! I'm a very simple person. The VR tubes are for the gate of a MOSFET source follower.

. . . . or consider a regulator circuit using a compactron ? A regulator using triode, tetrode or pentode can be built with only a few supporting parts under the hood so the aesthetic could be a vision of compactron purity.

...but I like the glowy tubes!

Well, I tried to desolder a 1982 date code 0D3 tube. There's something bonding the base to the tube that I can't readily see. I'll just have to live with the tube bases. Maybe I'll paint them as the VR tubes don't heat up much
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I get it about liking the "glowy tubes". Too bad they didn't make compactron mercury vapor rectifiers. That would be a pretty sight.

People on other forums (like old radio restoration sites) have talked about soaking the base in solvent to get it off cleanly . . . . .

What about mounting the socket enough below the level of the plate that the base doesn't show topside? . . . . Or skip mounting a socket on a sub plate and use a capacitor clamp to hold the base of the tube directly . . . . .
How about a zener diode feeding a compactron k-follower, or triode-pentode error amp and follower? Plenty of cheap stuff in compactrons that will work - perfect job for a 6LU8. Find one with cobalt in the glass and you even get the blue glow (Although thats hit or miss, and tends to require plate voltages on the high side of things).
For the adventurist & curious why not try some neon bulbs from the past?
And add color & flashing lights to your project,
The list of prices is from a 1960 catalogue The pdf is a 'how to' document.
Many odd circuits are possible,
There was a 3-terminal device that looked like an NE2 but I've not been able to find any data,
Logic circuits were possible, one of the guys in the lab built a small running demo circa 1960.:LOL:


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I've resigned myself to using the 0D3 VR tubes because:

1) Got a bunch of those suckers
2) Got a bunch of 2SK2700 MOSFETs
3) Ain't got no neon bulbs
3) Simple circuits to you guys and gals are likely too complicated for this guy with a life sciences background

I'm gonna tell myself that the 0D3s are compactrons wearing pants. I'll paint the bases denim blue and make goggles...


eh, no.
I thought the issue with neon was noise. Isn't that the reason they are not more venerated by tube amp builders?
Noise is always an issue concerning any sort of glow discharge. However, the noise is much less objectionable than that produced by the reverse conduction through a Zener. I've used glow tubes as references for active screen regulators, and noise isn't an issue here. As for why, there are very few commercial designs that used any sort of screen regulation, and some of the few I've seen have been professional gear, not consumer. It's cheaper to use types designed to eun the plate and screen at the same voltages without screen regulation.
Noise is a concern, but when you look at the ratio of the noise voltage density to the DC voltage, glow discharge tubes outperform most modern voltage references. When you look at that ratio, a typical 21st century bandgap reference is far more noisy than an 85A2 reference tube from many decades ago.
But with SS reference devices noise can be suppressed just by parelleling a capacitor of sufficient value. To have some fun, try this with a discharge tube ;) .

I disagree with the suggestion of simple neon bulbs like NE2 etc. The almost constant voltage over a wide current range results from the large cathode area of VR tubes, which neon bulbs don't feature.

Best regards!