hello all, I've been charged with the task of figuring out what's wrong with this amplifier and determining what needs to be done to repair it. There is some weird buzzing that apparently happens in the higher register of the amp at random times (I haven't played through it yet). I've perused the forum and the possibilities seem to be bad biasing or failing components inside of the amp. Below is a low quality sound clip that the guy who asked me to figure it out made for our local music shop. They couldn't find the problem. One tube has been replaced (not sure if it was the 12ax7 or the 12au7) since the problem has started and it didn't fix it. As far as I know, the buzzing is heard even from the direct out. Thanks a ton in advance. I know if anybody can figure this out it's the experts here on the forum. I'm hoping to use this as a learning experience as well as do a favor for a friend.