Yes, I know that tapping tubes is a much more severe G load than typical air loads can impart. However, it is significantly closer in magnitude to conceivable chassis-borne vibrations. (Have you ever put your hand on your preamp's chassis while loud music is playing?) Still higher, I grant you, but this is really a matter of simple physics. In fact, one of the simplest of all physical equations. Namely, that a specific force will cause an acceleration (and yes, a subsequent ringing) that is exactly proportional to the magnitude of that force. Moreover, a simple fingernail tap is about as close to a step function as you can get in a no-cost test, which has all kinds of benefits in analyzing how a tube (or any other physical/electrical system) reacts to transient perturbations (which is about as close to a general definition of a musical signal as you can get). So yes, the test I proposed is more severe than the tubes are going to see in normal service, but it is nevertheless a totally valid way of easily demonstrating that tubes are indeed sensitive to vibration. Anyone who denies this as an absolute impossibility has their head in the sand. (And I'm being polite here.) Go reread Hee's post above and then tell me that this problem doesn't exist.
