Hi Guys, I have a 67 Proreverb which was gone over from tubes to caps and new speakers just a few years ago. It hasn't seen much use due to a change in jobs but I got it out last week and it still sounds wonderful. But it appeared that one of the 12AT7's was microphonic so I bought a couple of new GT12AT7's and put them in v3 & v6. It has GT's throughout with an ECC83 in the v2 slot. But it is slightly microphonic. You can tap on all of the preamp tubes and get a deffernt new noise that with continued light tapping will cause the noise to go away. You can even tap on the volume knob with it turned down and hear the noise. Now its not alot of noise but it is still there.... I even thought it could be the crappy ac here so I brought out an old UPS we used for a video editing suite. Its quite large and has new batteries. Still the problem persist! The tech is a great guy but he's on the road and I am not sure what to do next. Its not a major distraction but my fear is that something may be loos and cause a major problem if not addressed. Any thoughts or ideas? Thanks, James ps: Here's a jpg of the amp.