so, i'm assuming the smashup does not address the microphonics issue.
Correct. The Smashup is adding C4S to the circuitry. Nothing to do with microphonics. The 4P1L is known to be microphonic. There are mechanical "fixes" that mitigate, (some which, IIRC, you have tried), and some "starve the filaments" in other circuits to minimize. But microphonics are inherent with this tube.
The Smash is a great line stage, even better with the Smashup, but the tubes are microphonic. I have minimized the issue by adding weight to the plate. I also made it worse, when changing volume and switching inputs, by adding different attenuator and selector switches. But I live with that reality due to the improvement in the sound. I have no issues once the tubes settle down after switching inputs or volume.
Roger, are you having issues such that the microphonics intrude when music is playing? Rather than hijack this thread, perhaps we should start a thread to discuss the microphonics and fixes that folks are employing.
Cheers,
Geary