Generally, all tubes are susceptible to distortions caused by micro-vibrations and microphonics. This will vary amongst individual tubes and components. For each person that we've had report that damping the input tubes made the greatest difference, another has indicated that damping output tubes made the most difference.
With all factors equal, I recommend damping the rectifier tube first. Damping the rectifier is usually significant and often influences an improvement with the other tubes as well. Next the input, then the output if you feel your system still needs a further nudge in the direction it's going.
Because tubes work together in a complementary manner, sometimes you don't realize the full potential of damping say, just the input tubes. Though reducing grunge significantly at the input, some grunge is put right back again at the output. And vice-versa; if you're amplifying a grungy pre-amplified signal, it will be grungy no matter how pure the amplification itself is at the power tubes.
Steve
Herbie's Audio Lab
