Microphonic tubes??

Can any body tell me anything about microphonic tubes. I have a Randall protube 1001 all tube .If you tap on the top of the head you can hear it through the cab. Please help.

Don't hijack someone's thread with an unrelated topic! :mad:

I have split your post off to start this new thread.

When I was researching tubes for my preamp I got the impression that microphonic tubes were a bad thing. Maybe I read it wrong.

All tubes are microphonic to some degree. If vibration causes the internal elements to move, that appears as noise at the output. Good tubes don't make much noise at all. Bad ones will howl so much that they can cause your amp to feed-back uncontrolably!