JCM800s seem to vary big time. I had a 50w, 2x12 master volume combo years and it was killer. Bought it from a dude in St Reatham who had two and the other one was shite. They had them at the Westbourne rehearsal studios too and their’s were a bit mixed.
In other news, I had band practice on Friday night... Was playing through an old JCM800, it sounded bloody rubbish...