My amp is working again, and I still get the hum. I have checked all the continuity and all is correct. The spare room does have a lot of fairly big transformers running (amps, lighting etc) so I think it is a noisy environment, plus the guitar amp transformer has become a touch rattly as soem of the laminations have got loose with time, and so this may be contributing.
Anyway, back to the main point, having had more of a play with these Mules I'm even more impressed, they are just so alive! I know what Tim means about the "on the edge" sound of the unpotted pickups, the upper mids alays sound on the verge of feeding back, but not quite. If anyone has the 3 volume live Fleetwood Mac CDs the edgey sound that Peter Green has on stuff like Jumpin at Shadows is the sort of thing. I can't wait to crank the amp up in the studio on Sunday, it is a shame I only have 1 lead left to record and some rhythm bits, I'd like to re-record all my solos with these on, but we don't have the money or time!