Hi folks,
I've just recently bought a little Mark III ( brand new, £560 later ) and I'm also getting "cut out " problems. At a gig amp switched on Ok .... sound checked ok... went to play 1st n.o .....nothing, no light just dead, Nightmare, switched the power cord , amp came back to life, assumed it was a fuse. Finished gig with after a little volume fluctuation, tested origional power lead fuse was fine!
Fortunately I filled out the warranty so it will be sent back for repair. Will let you know what happens.