I've got a friend who has been fixing those things since he was a kid in the 1950s... I've been helping him recently, it's an ersatz apprenticeship.
Almost everything is now well beyond economic repair. It's all about emotions and nostalgia for almost all of the gear.
I no longer jump when something smokes or pops, and I know it's usually a good sign, as it helps you figure out where the trouble is. ;-)
I've learned to hate Silver Mica capacitors, and came up with a technique to help track down the noisy ones. (Take out all of the tubes, leave B+ on... measure the voltage across all the resistors, most of them will read 0 volts, if you do get a voltage, check the schematic and see if it's reasonable, if not... there's current flowing to a bad silver-mica cap through it. It really cut down on the time to find issues)
Collins 30S1 amplifiers.... those will always command fear and extreme caution. 3000 volts at a solid Amp will easily burn off limbs, and it will hurt like hell as you watch it happen to you. Or... it'll just kill you, and burn your corpse.