can i ask how you find the tone stack on the marshall? it's one of the few valve heads with a proper active one and i'm doing something similar with the next head i'm building for myself
Very rare, I have the last two left in UK.
Got mine up for sale if anyone interested.
https://www.ebay.co.uk/itm/Marshall-Bass-400-watt-Amp-2-4x12-Celestion-Sidewinder-600-watt-cabs-1980s/293461419180