tubes age 25
>I don't think I've ever seen one shorted,
About the only way that one could short would be to have had a bad internal
weld and resulting loose "pieces" rattling around inside of the envelope.
There's so much clearance in one that it isn't funny.
>most of the time their failure is one of lousy voltage regulation or oscillation.
Agreed. I've seen a lot of regulation problems. ;-(
>Either of those is probably from a change in gas pressure.
You know, I've often wondered about something Doc. I know that a lot of neon
lamps have a trace of a radioactive isotope in them to help the ionization
process and I know that a majority of the 0A2's have a hint of radioactivity. There
are three different commonly used isotopes, depending on the mfg of the tube.
I suspect that it's for the same purpose as used in the neon lamps. At any rate,
I was digging around a while back and noticed that the half life of one of these
isotopes was only ten or twelve years. Since I doubt that a new 0A2 has been
made in 15 years or better, some of these are getting "old". Any ideas on how
this could effect the tubes Doc? I'm guessing that it might cause a higher
voltage requirement to initially fire the gas and maybe some instability until it
had warmed up but I ain't no engineer. ;-)
Do you think that it could have a noticeable impact on the performance of the
regulator even after it's run for a while? More prone to faulty regulation or
oscillation? Do you think it might be worth avoiding the mfg tubes that use the
isotopes with the short half life?
> > jumpers will do it. You might want to put a scope on it too. I've found noisy
ones using a scope >>before. A scope is a good idea because one failure
mode is oscillating. The VR tubes normally >>have a negative resistance
region in their curve and if the current through the tube gets too >>low and the
capacitor across the tube is too large it makes a great neon bulb type relaxation
>>oscillator.
It took me an awful long time to track down the problem the first time I had a
noisy one. I had measured the regulated voltage and it was right. I never
suspected the 0A2 could be a source of audio noise. I ended up swapping out
the audio module after I couldn't find the problem. The problem went away so, I
swapped the caps and then the tubes in the decks and reinstalled the original
deck. I did a tube by tube swap and found that the noise "went" with the 0A2.
After you've had one, you don't forget. I had a noisy 0B2 in one of the antenna
couplers a few years back and a real nasty problem with either an 85A2 or
5651 in the Tektronix scope a few years ago with screen "noise". That design
one glows orange and is a neon filled one. I've seen only one of two of the old
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