[Boatanchors] Ques on vacuum tube storage/aging?

[Steve Uhrig]

Hi all,

Recently I ran across an article on the web which I did not bookmark, 
written by a gentleman who had a PA tube in an amplifier fail 
apparently from having been in storage for a decade or more. His 
claim was the hermetic (glass to metal) seals around the pins aren't 
perfect and oxygen molecules leaked in making it gassy.

He theorized if the tube is operated periodically it will last much 
longer because the getter will absorb a few oxygen molecules which 
leak in, but if left stagnant for too long, too much oxygen will leak 
in, more than the getter can absorb, and make the tube gassy.

I entered electronics about the time things were transitioning from 
tubes to solid state. I know laser tubes need to be operated 
periodically to keep them happy as their seals leak, and it's well 
known the Nanao CRT ICOM used in their R9000 receiver went bad with 
calendar time as well as hours of use. But I don't know how small 
signal tubes fare in this manner.

And I thought the getter was fired once when the tube was 
manufactured, did it's thing in milliseconds and that was it. What's 
the story on this? Does the getter continue to absorb oxygen? If so, 
does the getter need heat to function?

Should I pull the precious older stuff out of deep storage and run it 
periodically, like my novice Drake 2B receiver? I am aware of the 
capacitor issue and reforming them, of course, but I'm asking about 
the tubes here.

My friend who restores lovely 1930 and later vintage consumer 
receivers has used NOS tubes from pre - WW2 days and had no problems. 
I have also, but it's been a good while since I did enough with 
things to remember any bad tubes, and then I could test them at the 
drugstore.

What say anyone on this? Several of us are curious. With some tubes 
becoming an expensive commodity, I don't want them to die in storage. 
20 years from now I may need one to replace in my 2B.

Tks ... Steve WA3SWS


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Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
mailto:Steve at swssec.com  website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
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