Marakanetz: I don't agree that subjectively dubbing a tube component "well-designed" has much to do with whether or not you'll find any symptoms arising from resonance problems which are inherent within the tubes, not the amps. Some evidence of this might be noted in the fact that ARC itself installs tube dampers on the gain tubes in their amps. It's true that amp chassis and PCB's can be designed with higher or lower rigidity, and internal suspension and damping measures may or may not be taken, but those last two can also be effected externally as tweaks, and whether the first factor winds up aggravating tube resonances or not is probably as much a result of chance as of design. Regardless, tube microphony will in theory always have some deleterious effects on the music (even with tubes passing the tap test), which no amount of component engineering or heroic construction can eliminate, so I think experimenting with tube damping is never inappropriate.
Pbb: I can't guarantee anything of course, but I'll tell you that what pushed it over the edge for me, as far as confirming results goes, was listening to prominently-mixed, well-recorded vocals in a sparse instrumental setting. (Solo piano is good too - live piano usually sounds mellower than most recordings played through most systems.) With the tube dampers installed, vocals sounded more like voices coming to me only through air ; without the dampers, they sounded more obviously like microphones were interposed. Since microphones *are* of course in between us and the singers, the presentation which is more 'correct' must be a judgement open to debate, but at least with my amps in my system, I am finding the sound more natural with the dampers fitted, and suspect the 'microphonic' quality I'm taming literally originates with the tubes. Anyway, the differences I'm hearing (again, with my amps and system) ain't huge, only subtle, but they are pervasive and perceivable, and I would suggest you try again sometime to listen for 'em...
