Sorry for a 4 year bump, but this is the first time I've ever seen what's happening at the back of his amps. So I couldn't resist posting here until now. Now! The important thing that the one who took the picture missed out on, is the OHM setting that the speaker cable goes out from the amp to the speaker cab. I've read just once in an interview (way way back...in 1987) that he runs them out from the 4 Ohm output of the amp into the 8 Ohm input of the cabinet! An impedance mismatch! Thus, not running them 100 W efficiently enough, but as Marshall OT's are sturdy enough to cope with upward mismatch without frying, it works. And that this was the most crucial element to his lead sound. That's what makes it "muddy" or no-trebly sounding. The other way wouldn't work, i e 8 ohm out into 4 ohm speakers, it would fry the OT and amp, if not the speakers too. I don't know if he still runs them that way today or not, and makes that "mod" his last clandestine, or secret trick, so no one can copy it or be able to tell. One can't tell how the speakers are wired inside anyway, so the readings on the panels will not give a clue. Is there anyone who have any insight on this?