Marshall JMP 50w Tremolo Plexi Panel "JTM50" 1967, Black

This Plexi-era Marshall 50w Tremolo presents itself in an unassuming way, but has an impressive set of features lurking under the hood! This amp was made during a transition period at Marshall, as they moved from the earlier JTM45 designs to the later JMP50/100 models. In between those models, you'll find the rare JTM50 offshoot. Factory-built JTM50 amps feature a special "Black Flag" JTM logo and are extremely rare—but if you know what to look for, there are a good handful of amps that fit the same criteria. 

Like the JTM50, this 50w Tremolo has the full JTM45 preamp circuitry, along with EL34 power tubes and a GZ34 rectifier. Compared to the JMP 1987 circuit from 1968, this amp still has a shared cathode preamp, a 56k slope resistor on the tone stack, and larger 0.1uf caps in the phase inverter. The result is less aggressive gain than the '68 Plexi, but it still delivers the great power and midrange response of the EL34 tubes, compared to the softer KT66 sound of the JTM45. Factory-built JTM50 Marshalls might have slightly different transformer combinations (PT: 1202-133, OT: 784-139), but many say the difference is negligible—most of the sound comes from the combo of JTM45 circuit, EL34 tubes, and GZ34 rectifier.

You may have noticed the tremolo feature hasn't been discussed—simply because most people aren't interested in that aspect. As with many tremolo-equipped Marshalls, the tremolo in this amp has been disabled to optimize the authentic 'Plexi sound. Internally, the electrolytic caps, power tube, and rectifier sockets have been replaced. The original pilot light and fuse holders have also been swapped out.