A plexiglass panel Marshall JMP 50W (bass) head from 1967. No bells or whistles here: four inputs and a blues/rock tone to die for. Very smooth and purring breakup compared to the later JMP's (the ones made in the early 70's etc). This amp uses significantly lower power supply filtering compared to later models that followed. This causes the amp to feel "spongier" as opposed to the tighter-sounding units with increased filtering. Also, these early models don't break up as soon so you'll have to run them pretty loud before you get the crunch - but it's worth it, I guarantee!
The electrolytic caps have been replaced and the amp has otherwise been fully serviced in November 2011. Also a bias trimmer was added for greater versatility.
Specifications
Marshall Amps Info & Schematics
s/n: S/ 10688