These amps are worlds away from a plexi. This is a take on the famous José circuit.
The voicing is not the same, the distortion is generated by the preamp mostly (three hot stages (2.7k/0.68uf)x2 and (820 ohms/don't remember about decoupling). Basically it's a really hot and tight jcm 800.
Though I have to say, After seeing the circuit I'm not to impressed. Way to much treble cut early in the amp. Could be done better to avoid killing to much of the Marshall character but still keep the harshness of the dual 2.7k/0.68uf stages at bay. Well well, the guy makes a living and you guys seem to enjoy his amps. I'd take a soldano or a bogner over this any day though.