Just picked this up at the weekend. A very lucky local find. Used it at rehearsals last night after some basic testing. It sounds absolutely spectacular. Blazing bright and clear with a Les Paul and my old 345. I'm having a good look inside now to see what jobs I need to do. Big Filter caps look original. I know it went back to Marshall some years back for a speaker change but there does seem to be a couple of other changes done. Hoping the experts on this circuit might shed some light on them.