I bought a used PF-500/210HE combo very recently from Guitar Center. First show, it started cutting in and out. I just picked it up from repair yesterday and went straight to a gig. It happened again but worse! The repair center is an authorized Ampeg shop. They replaced the circuit board. I'm at a loss. I'm an Ampeg guy. I've always used the older stuff. This thing is a lemon. I want to get another, but I don't trust it anymore. Bummer city.