First thing to do is to find out which model MosFet you got, they made more then one model as far as I know.
Then i would find the correct circuit for it.
Try DrTubes website for the circuit to start with.
https://drtube.com/en/library/schematics/69-marshall-schemas
Once we know what you have we can make better guesses
Then i would find the correct circuit for it.
Try DrTubes website for the circuit to start with.
https://drtube.com/en/library/schematics/69-marshall-schemas
Once we know what you have we can make better guesses