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In the Forum:
Melquiades Amplifier
In the Thread:
Gas voltage reference 0A2 tubes.
Post Subject:
VR tubes stability
Posted by
Jack 14
on: 9/9/2005
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Hi Dima,
Yep, I really think that I get this one right: I never take the time to do any research about it until your posting came. Luckily, I got the clues in less than 15 minutes. If only other things can be like that...
About VR tubes stability, now:
I have read a long, long time ago, that if someone need a reliable (ionisation voltage stability and noise) VR tube, that this one have to be AGED few hundreds hours (e.g. operated near maximum current in a burn-in fixture). It was reported to stabilise both internal gas mixture pressure and ionisation characteristics, making the tube more "repeatable" in it's characteristics and less noisy.
When I was younger -35 years ago-, I have observed the glowing of a NEW VR tube (it was a 0C2) for few hours (ok, I had nothing more interesting to do then..) and seen that at low currents, especially, the ionisation path moves itself randomly between the tubes elements (the ionisation density is never equally distributed vs the element's surface) and that this displacement was translated as small variations of the operating voltage accross. An "old" one does not behaved like this, seeming to have a "preference path" between it's elements. But, interestingly, both were sensitive to magnetic fields (I disturbed the ionisation path at will with a small magnet, creating suddent voltage jumps across the tube).
That 0C2 was used in the regulated
tube
Power Supply I've made to "feed" my Wireless Set #19MkIII (That I operated "bootleg" with few friends having the same setup: the whole kit was sold for $50 in army surplus depots at the time) and I had to readjust the output voltage (B+1 - 275V) periodically when I used the new VR tube, but not with the old. Few months of operation later, the new tube was stable as a rock. I have also used a
steel
shield around that tube to cut the magnetic field's influences.
I also have some '50 vintage RCA 0B2WAs, with the boxes stamped "AGED". When I used one, I observed a stable ionisation path within.
To sum up, it seems that if you want a stable VR tube, you should age it a few hundred hours and shield it against magnetic fields. Is it making any sense to you ? I do not see why the 5651 cannot behaves similarly. Was your "bad" tube a never used one ?
Have fun, but beware of the gases !
J14
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