Ever see a power tube getting rebuilt? Didja know it could be done? One of my favorite tube rebuilders, Kennetron, has a bit of a virtual tour of their plant!
Sure, there are other rebuilders; many years ago, I used Econco for big Class C power tubes in FM service (now a wholly-owned division of CPI, which also owns Eimac, it looks like they have dropped their old, irreverent "use a transistor, go to jail" tagline) and I've always heard good things about Freeland Products. Still, I have a soft spot for Kennetron, who have so far been the only outfit willing to take on rebuilding small (1000 Watt!) ceramic external-anode power tetrodes used at ultra high frequencies in Class AB1 -- and their rebuilds work! This is a fussy task, combining the skills of jeweler, machinist, welder and more for devices that operate in about the same power range as chainsaws.
It's a heck of a thing to send in old, worn-out, even shorted "empties" and get 'em back at half the price or less of new tubes, ready to go.
Power tube rebuilders are a scarce breed. The collection of skills and equipment to do the job, from vacuum engineering to glass building to fabricating the intricate internal assemblies, is rare and unlikely -- we're lucky there are at least three left!