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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Conn Caprice 427 needs new 12AU7 tubes—advice?

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Hmm, after a little investigation, I found that the tubes aren't really as shot as I thought they were. Turns out a pin had fallen out, breaking a circuit and disabling a lever that controlled the great's bright/mellow timbre. After replacing that pin, the whole organ seemed to come back to life. Weird.

There's still an issue with the pedal controlling the tremolo rather than the volume, but I'll post that to a different forum here.

Removing all the tubes carefully with plastic gloves, wiping the dust off them with a dry paper towel, and then reinserting them seemed to kill a loud hum the organ made. It also brought the volume up from a measly mumble to a wonderfully melodious shout.

Some of the tubes are still having problems, though, so I think I will buy a few new tubes. Would you recommend going on the cheap side or shooting for the more-expensive tubes?
 
I feel that a tube is a tube. The manufacturer meets the specifications so that should end the discussion. Further, tubes will probably outlast most of the other components if they aren't abused.

It appears you may have some marginal tube sockets, however. Rock the tubes in their sockets and that could fix a lot of problems. It certainly cured all the problems my old Ampex tape deck had. Finally, run them through a tube tester to remove doubt.
 
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