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Inmates;
I have been running a tube 'something or other' for 50+ years now and in the time have been slowly collecting tubes that interest me.
I occasionally sort and inventory tubes and in doing so recently found I had exactly two quad (eight total) GE 7027a tubes. I like the 7027a in my Mac MC240 as it has (to my ears) a more solid base signature and seems expanded through the whole range. I usually run RCA's but obviously asquired these GEs along the way.
I am fairly certain that no more than any two of these were acquired together but each and every one is showing a fair amount of gettering dissipation (dual side getters). Has anyone seen a situation where GE tubes don't age as well as others?
All tubes test fine in my simple tester (Superior Instruments TD-55) but I recognize it is not the last word in test equipment. Obviously a disappearing gettering is not desirable but assuming the tube tests fine otherwise is it 'wise' to use it?
Finally, is there someone recommended in the community who offers excellent tube testing services? These are of high enough value to me that I would like to have them seriously tested by someone in the know with serious equipment.
Thanks you
James
Follow Ups:
It might be possible to give a more relevant answer if you were to post a photo of the tube(s).
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Buy Chinese. Bury freedom.
Well, don't take my word for gospel, but I've heard that the getter could fade a bit due to three big reasons: A) the vacuum was a little contaminated at the time of production, and over time the getter scoured that away; B) there's a a manufacturing defect which caused a VERY TINY supply of air to get drawn into the tube; or C) the getter wasn't activated properly to begin with.
Now, if its discoloration - like a rainbowing - it's fine. That's normal. That's the getter doing its job, as per case A). I've seen it, too. I've given the stink-eye to more than one tube like that, but nothing blew up in the end. Only once did I have rainbowing AND bad performance. It was a pair of Sovtek KT88s (those aren't worth their salt, anyway, so it's not a mystery).
For B), use may or may not affect the stability and longevity of the tube. If it was a glass-base pin that was sort of off, then heat could expand materials and cease the leak altogether. On the other hand, installing the tube may stress those pins, and exacerbate the problem.
For C), GE's microwave getter-activator machine thing had a bad day, the getter seems weird, especially with age, but the tube is fine
As for testing, I agree, there's nothing except a real world test that will show if the tubes are 100%. The only serious testers I've seen lately are Maxi Test products... That will test at about 400V B+ and allow you to reach a good dissipation. Anything else may still be under-the-cut for "real world" conditions.
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May your tubes be warm, long-lasting, and always lively. Holy be thy heater.
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