#3
Thats a Marshall solid state head. No tubes. I've never played it, but as a rule solid-state marshall amps are not worth the time of day. I'd look else where
Framus Cobra
Marshall JCM 900
peavey 5150

Mesa 4x12
#4
Mosfet amps are not exactly like the modern SS junk marshall is selling now. Some of em were actually pretty good. They arent tube amps. But there was a time in 80s when replacement tubes could be hard to come by. So mosfets were used. I think randall had some mosfet amps to.