I had a gig that required carrying equipment up a two-stories of stairs and opted to leave my regular gear at home and go with my Ampeg 115HPT (which was no piece of cake getting up those stairs, either). I've only used the 115 to practice at home and have never used it on a gig. I turned it on and it worked as normal. I cranked up the volume a little and it did fine. After about 10 minutes the volume started decreasing (very slowly at first) to where the bass guitar was barely audible. Luckily, I was able to DI to the FOH and everything was fine for the gig. Has anyone had any similar experiences, or may know what has happened? Thanks in advance.