Hi Colin,
As to the hum. there is something funky about those pots. this is not the second of third time they have thrown a curve. I ended up tieing my chasse ground to signel ground. With my high tech chasse covered with space age teflon.the pot may or may have not had contact with the steel. the connection didn't increase the noise so I left it. try a clip lead and see.ESD is probably what got the fets. with this cold dry air, zap.
the amp was unpluged for a full day PS down to 0 on its own. Fet's are sensitive this is one reason you see zener clamping diodes on some CCS circuts I would like to get another set. let me pay for them this time as you were kind enough to get them.
On the amp front I just converted my JE labs/ FI 300b to WE type 91 and I like it a lot. I have a DRD project in the pipeline. still colecting parts.
I am going to follow along and see. I have some 6a5's I want to use and I want to fool with a transformer phase spliter and parts on hand. But who knows, Dougles is a master of push pull amps and I want to see what kind of transformers are brewing...John