John said:
"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."
In the case of the 15GP22... The getters appear to be the "stirrup" style mounted in the neck... looks like there are 6. IIRC, not all getters were exothermic.
"Any barium left to flash will be minimal and you have a lot of gas to deal with."
I 100% agree with this. But if the tube were mine and I had an RF generator, and a getter "wand" I would try it.
"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."
Back in my old "poor starving young engineer" days, I kept an old CTC-4 going by re-flashing and re-activating the 6CB5 HO tubes several times (darn things were expensive and I had access to an "engineering tube lab")... your experiment sounds like fun
jr