Quote:
Originally Posted by jr_tech
I think that there might be a couple of reasons to proceed with caution.
1. Liability... I really would not want to be the person operating the CRT checker, if that test blows the heaters, unless the owner of the tube fully understands the the possibility that the test might "finish off" the tube. 
2. If the heaters blow it is indeed "game over" for the tube (except for rebuild). If they are intact, there still might be a very slim possibility to save it... Perhaps Scotty can re-flash the getters? 
just my 2cents (or less) worth,
jr |
The issue of dealing with an irate seller who thinks you just blew his 15GP22 is certainly a worry. A noisy hand held Tesla coil might have him wondering too.
As far as "game over" or not... I'm skipping definition of terms because I know you're very knowledgeable technically.
The getter flash probably has a capacity of a few hundred liter-microns before it is used up. If the getter flash is gone you've probably had that much air enter. It's less effective for nitrogen, the few hundred liter-micron figure is for oxygen. You probably have at least a few hundred liter-microns of air to deal with once you find a gassy 15GP22.
I'm not sure how the getter in the 15GP22 is made, but it's probably a large ring at the end of the gun. The ring could be a channel or a tube. If it's a tube then it has a thin wall that bursts when it's heated and the barium evaporates out. If it's a channel, then it's probably a stable barium alloy like BaAl4, that reacts exothermically with a nickel support once above 800C and quickly reaches higher temperatures evaporating the barium. Nickel powder is also added to BaAl4 powder, but I don't think this technology existed then.
Any barium left to flash will be minimal and you have a lot of gas to deal with.
The cathodes will be deactivated. During the activation barium oxide is reduced to barium forming a thin layer of barium metal on the barium oxide. Any metallic barium will have turned to an oxide if the tube was gassy. It is reduced either by silicon that was added to it or by the nickel cathode base metal. The nickel will have formed some nickel oxide and might prevent another reduction of the barium oxide.
I have a bunch of 6J6's that have air in them. I've thought about adding a pump-out and see if I can reactivate the cathodes. I suspect it won't work, but it would be fun to try. Finding the time is hard though.
John