Microphonics is the vibration of the tube’s glass, which introduces itself into the signal?Microphonics has more to do with how the internal structure deals with vibration. It does come through the glass, but damping the glass does little if the tube is microphonic.
is that the purpose of the damper rings I see around some tubes? You’re saying it’s more of an issue on 6H30’s more than other tubes?
If you’ve been buying tubes from a manufacturer like ARC, the tubes are already hand-picked for low microphonics, which relates directly to their cost. I’m seeing this from a production point of view; when we buy 100 tubes at a time, its nice if you can use most of them. Some tubes (like the 6H30) simply have a higher rejection rate on account of microphonics.