Microphonic caps?

[dartanion]

This is actually pretty common. There is no attenuation on that first gain stage, so whatever "noise" is present usually comes through and is amplified. There are many ways to counteract it, but it is still a frustrating feature of running an amp at the hairy edge of stability. Some of the best sounding wreck style amps that I've build have been the ones that were a challenge to bring under control and also most difficult to find a usable V1. Lots of folks use lower gain tubes throughout the preamp and PI to tame things, some use snubbers, some goop, some beargrease, you know, whatever works baby!