Tube microphonics

It must be hard to try or the OP would have tried it rather than starting a thread.  but maybe his real question is "what is microphonics"....

I test all my tubes for microphonics and reject any tube that exhibits audible microphonics.  "Microphonics" is then the tube acts like a microphone.  when it is excited by sound or vibration, you hear it in the system.  Easy to test for, put the tube in, turn on the systme with nothing playing,  and tap it lightly with your finger nail or a pencil.  If you hear it (coming out of the speaker) that is microphonics. 

So if your tubes can be excited by sound, the music itself can cause noise.

Jerry

@tattooedtrackman So just test for microphonics in all your tubes as I described.

people posting their experience with microphonics.  The worst offender in my experience is OS (they are never really New) 6SN7.

Jerry

@mulveling  Exactly.  Because of their position in the signal path, any noise shows up in the speaker.  

Yes, I've returned some 6sn7s for microphonics.  but I eventually found a couple of pair that were very nice.  the 6922 and equivalents I haven't found to be very microphonic, just poor noise floor on some tubes.  but they are in the same challenging spot in the signal path.

Jerry