Back in the ‘80s, when the underground had not yet been co-opted, and the temperature was low enough that there could be reasonable discourse and a genuine attempt at understanding.
edit: thankfully, the commercials have been retained.
So let’s get the playing out of the way first. Astounding.
But this was done on a Marshall Plexi. If you know about the topology of that amp, and the gain staging, it becomes a whole other world of unbelievable.
The clipping harmonics in the power valves, the shading...and how string attack can be used to influence the sag of the variac. To me, it’s beyond explanation or understanding.