So I replicated my '83 2204 CSA in an old solid state 5010 chassis. Fired it up and no smoke, flip the standby switch and I get a 120hz hum. - the hum is constant and is not affected by the EQ, preamp or master volume; - pulling V1 and V2 makes no difference; - pulling V3, the phase inverter kills the noise completely. - removing the center lead from the master volume almost kills the hum - with the V3 installed: - removing the lead from pin 1 almost kills the hum - removing the lead from pin 6 almost kills the hum - removing either leads 2 or 7 reduce the hum volume a bit Any suggestions.... all grounding is as per the original amp. EDIT - Fixed.... forgot to ground the speaker jack sleeve to the chassis. THIS THING IS AMAZING !