getter flash peeling/crinkled ?

[ALBATROS1234]

i came across a set of 4 rca 6973 tubes on fleabay for $10. they all test close to or above nos values. the disclaimer stated was that the getter flashes were thinning and starting to turn a bit brownish in spots. so i took a shot because it was $10 for 4 6973 tubes which is one of my favorite power tubes. i got them in today and they all sound great, just like a 6973 should but i noticed one of them the top getter seems to be separating slightly from the top of the tube . it looks like extremely thin alum foil kinda pursed away from the glass in spots. it sounds fine. i read up and there is mixed opinions about getters in general some guys say if the getter flash is thinning or brownish tinted this means the tube is worn out and has been abused. other guys say they have seen true nos tubes that looked like this and it means nothing what counts is what the tube tests at.  i have a 12at7 which the getter flash is solid chocolate brown but it sounds and works perfect for well over a year. i am just curious about what you guys think and also has anyone seen a crinkled one starting to separate from the glass like this one i have? thank you for your time and expertise in commenting.

[jjasilli]

Hope they work out.  Please let us know how long these tubes last.  I have gotten conflicting info on how to judge the quality of getters, leaving me dazed and confused.  If the getter is going bad, the tube is approaching failure, even if its other parameters are good. 


Probably getters go bad because they're dong their job of absorbing gas in the tube.  Tubes can only get more gassy over time, and getters can absorb only so much gas.

[galaxiex]

I thought the getter was flashed during manufacture and didn't do much after that.

Do I have wrong information?

[jjasilli]

Your info is not wrong, but is incomplete.  See:  https://en.wikipedia.org/wiki/Getter


"Getters are especially important in sealed systems, such as vacuum tubes. . . which must maintain a vacuum for a long time. This is because the inner surfaces of the container release absorbed gases for a long time after the vacuum is established. The getter continually removes this residual gas as it is produced. . . Small amounts of gas within a vacuum tube will ionize, causing undesired conduction leading to major malfunction. Small amounts of gas within a vacuum insulated panel can greatly compromise its insulation value. Getters help to maintain the vacuum."

Flashing is one method of applying a getter, and is the method used in vacuum tubes.

[PRR]

> I thought the getter was flashed during manufacture and didn't do much after that.

The vacuum in a vacuum tube is well below what the best pumps can do in any reasonable time. You can't actually "suck" below a certain pressure. When there are just a few atoms left, they do not bang into each other and take any available opening. They just wander around, the pump only sweeps them preferentially one way after they find the exit randomly.

The getter's first job is to absorb the gas that did not find the exit before the pump-exhaust was sealed off.

BUT there's gas absorbed in the metal and mica which continues to come out "forever". (There must be some limit but it may be more than a human lifetime.) The getter is sized to absorb that lingering gas at least as fast as it appears.

Brown means the getter has been absorbing gas. However the getter is always so over-sized that it can be 90+% brown and still have years of life left. Not To Panic.

A "peeling" getter is very odd. It should stick very well, being atomic fog deposited on hyper-clean glass. It will still work like that. However I wonder what happens if it flakes and falls into the tube guts. On plate-cathode it would just vaporize (re-vaporize). But the power in grid would not zap it, and short-out the signal. If it falls all to the bottom of an (true) Octal and stays at the base of the glass crimp, no harm. But in a Miniature (and some late 8-pins build the same way) it would lay on the leads.

[ALBATROS1234]

i am certainly a newbie when it comes to scrutinizing tubes closely although as a guitar player i have seen and handled them through my life. but have never seen anything like this crinkled tube. the getters on the others still have a fair amount of silver and metallic gray but there are brown areas as well as translucent areas mostly lower on the flash area, for tubes that are usually $40 to $70 a piece nos, if you can even find them, i rolled the dice and sacrificed the $10 plus shipping for 4 of these rare and amazing tubes. i do have 2 others which look better as far as getters and i bought used for a good deal and i liked them so much i wanted some more. wanted to show the crinkling in pics.