Hi Guys, The sound on my AC15CC changed suddenly during a gig. All through practice and the first song it sounded great, as soon as we hit the second song things were different. Whenever I picked a note, especially the lower strings EAD, the bass would ring out uncontrollably, as if the amp had lost all its definition and control. The sound had become mushy and instead of being tight and focused, sounded all muddy and lacked clarity. Does this sound like bad tubes? I have since replaced the preamp tubes with new ones and it didn't make much of a difference. The only ones left are the power tubes.