Tubes and microphonics

As a pratical matter, by ear. Microphonics will be revealed by tapping VERY lightly on glass tube with a pencil, but this may actually have no real world meaning if you hear something, but it will mean that they are not particularily microphonic if you hear nothing. You will also hear the effect of microphonic tubes when you are operating the switches on the electronics when you have high levels of microphonics.

IMHO, the most serious distortions caused by microphonic tubes, which you will not hear from "tapping or switching" are due to airborne vibrations and/or mechanical vibrations caused by playing music loudly and/or having externally transmitted physical vibrations enter the equipment. So crank up the volume and see what happens.

I just bought a new amp (Dehav,Aries g). I also bought some of those Herbie tube dampers--Oh ya, the ball footers too. Cheap enough. Makes me feel 'covered'.

If you hit stop on your CD player during a loud passage, and your speakers seem to ring for an instant before they go quiet, your tubes are microphonic. It's usually very obvious.

Jeff