Anyone had any issues with their PF series head "faulting"? I purchased my first when they hit the market, and loved it; after using for a year, the fault circuit starting tripping, and the amp lost signal power (AC was good, just no output). Ampeg replaced it under warranty; now I have the same issue with the replacement head. Has anyone had, or heard of anyone having, these issues? I'm huge fan of Ampeg, even owning other Ampeg units (SVT-450, 1966 B-15-N, 410HLF cab, (2) PF210 cabs), but this head (the PF-500) is really becoming frustrating....especially when it happens live! Thanks!