Herbie's Audio Lab has been working for quite a while on a more sensitive, compliant isolation pad for use exclusively with delicate small-signal tubes. We've finally achieved that goal with our new UltraSonic SS Damping Instruments. By eliminating the need for a stiff outer sleeve, the isolation pads maintain a more sensitive and intimate contact with the tube glass, achieving the most delicate vibration contol ever.
Small-signal tubes, especially 6922-type, are generally quite susceptible to microphonic and micro-vibration distortion. Likewise, they are sensitive to fine musical nuance that is oftentimes masked by a thin veil of microphonics. Unlifting this veil brings out the full potential of these tubes, which can be quite dramatically musical.
UltraSonic SS w/6922 tube (Siemens Cca)UltraSonics Link
For tube-gear music lovers, I recommend giving UltraSonic SS damping instruments a try on your small-signal tubes. Even if your tubes don't seem particularly "microphonic," you'll probably be pleasantly surprised with the musical improvement. For rectifier and power tubes, UltraSonic Rx or HAL-O III are the way to go.
Steve HerbelinHerbie's Audio Lab