[Boatanchors] Ques on vacuum tube storage/aging?

[Sandy W5TVW]

A lot of tubes benefit from just having their filaments/heater run
for a while before use.  Usually there isn't a problem in the smaller
receiving type tubes, as the "getter" flash remaining on the glass
will usually absorb the molecules.  Some of the larger transmitting
tubes benefit from running them with just heater voltage for
a hour or two before they are used after long storage.  This
seems to work especially well with graphite anode tubes like
the 805, 211, 813, etc.
Tubes like the 3-500Z, 4-65, 4-125, 4-250, 4-400, etc. have very high or
"hard" vacuums in them and are contructed of materials that usually 
don't absorb and gas molecules.  You will note also these tubes don't
have any "getters" in them either.
Truthfully, over the years, the only tubes I have noticed and large
difference in after long storage were 805, 810 and 813's.  All graphite
anode types.  When this occurred, I just ran them for a couple of hours with
filament voltage only.  They also seem to improve after a few hours of
service as well.
73,
Sandy W5TVW
----- Original Message ----- 
From: "Steve Uhrig" <Steve at swssec.com>
To: <boatanchors at mailman.qth.net>
Sent: Friday, May 14, 2004 12:39 PM
Subject: [Boatanchors] Ques on vacuum tube storage/aging?


| 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
| 
| 
| *******************************************************************
| 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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