I've been using a VOX VT15 for several years and it's generally worked fine. In the last few days I've had two 12ax7 preamp tubes go microphonic on me in this unit, which has never happened before. Just before this issue started, I pulled out an old Silvertone Silhouette from the 60s (?) that I hadn't played in years and plugged it in. Since my wife bought this guitar 10 years ago, it's always had inconsistent and woofy output. Could be a number of things and nobody can get to the bottom of it because the stupid pickups are bolted onto the pick guard and are encased in aluminum. We've always expected there were grounding issues with the guitar.My question is: could this guitar be causing the tubes to go microphonic? Sorry, I just noticed this is in the wrong forum.