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Marshall JMP model 1987 (1972)

Marshall JMP model 1987 (1972)

A metal panel Marshall JMP 50W Lead (model 1987) from 1972. This amp came to me with the most suspicious power tube configuration I've ever seen: a near-dead RCA 6L6G and a very strong Tungsram EL34. Also the bias resistor had drifted from 68k to 89k so the tubes couldn't be biased warm enough. Luckily my tech had a nice 47k carbon composition resistor as a replacement and now the bias trimmer has a usable range again. Also the fuse holders were replaced - and I'm glad we did that: one of the "fuses" was actually just a piece of aluminum foil crammed inside the holder. Talk about electrical safety!

The power transformer is an upright one. In 1972 Marshall used both laydown and upright power transformers and even though the laydown power transformers were more common in the early years of Marshall amps, some of the later '72 models have laydown transformers as well. Wonder why they put upright ones on some of the early '72 ones. My guess is that they put in whatever they had in stock at any given time.

There are six rare yellow Wima "chicklet" capacitors on the board as opposed to the all-mustard set you'd expect from most amps of the era. Marshall only used these capacitors in '72 and even then only in a handful of amps. Some say these capacitors sound a bit more aggressive than the "mustard" capacitors. I'm definitely not going to swap them out, to me they sound great! Funnily enough, the grid wires are orange as opposed to the usual green, but the solder joints seem untouched with red dye on top of them, so I have no reason to doubt their originality. All those facts combined it's no wonder that even though most old Marshalls sound great, they all sound a bit different! The amp has been fully serviced (including new electrolytic capacitors) in April 2012.


Marshall Amps Info & Schematics

s/n: S/A 2352D (March 13, 1972 is written on the inspection tag)

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