Starting work on a GE 800 Locomotive.

[kvflyer]

Originally Posted by Eric H

And a few more caps...
The vertical was cutting in and out when I tapped on the 12SN7 tube so I replaced it, it seems solid now, ...

Could that cutting out and tapping be a dirty tube socket, or possibly the tube that you took out having dirty pins?

I recently brought back to life a factory wired Dynaco PAS pre-amp. One channel was fine; the other was dead. I had not cleaned the sockets yet and wiggling one of the 12AX7 tubes brought it back temporarily.

Long story short, DeOxIt on a toothpick into each socket and all is well now.

Just a thought, could be still a good tube!