I recently received an Ampeg SVT-IIP preamp and have began to incorporate it into my setup. I love the tone I get from the tube preamp and everything sounds great, most of the time. The preamp begins to overdrive and distort the signal after running for a few minutes. This problem seems to come and go as I play through it. I have taken it apart and cleaned the inside and still have the same problem. Has anyone else had this issue with these preamps? Does anyone know what could be causing this or how to fix it to be more reliable? Thank you!