The label “JTM50” began to circulate in 1965 on the first 1963 Super P.A. heads, equipped with four channels and eight inputs, which sported also the label “MK III” on the front panel, the same present on the rear panel of the JTM 45/100 Super P.A. These amplifiers were still equipped with KT66 tubes and the change to the new name was purely for marketing reasons.
This 1963 Super P.A. features on the fornt panel "MK III" and "JTM50" labels, Courtesy of Amp Archives
In 1966, when the Mullard EL34 power tubes replaced the KT66 tubes, the “JTM45” logo was finally dropped for the “JTM50” logo, both in the heads and in the Marshall combos. Thanks to the new valves, but also to other small changes, which particularly concerned the transformers, the power was around 50 watts and justified the new label of these amplifiers. The sound, sharper and more suitable for distortions, moved farther and farther away from that of the first JTM45.
The JTM50, in a very short time, underwent changes in look and function, including new bright caps for the Lead version, but especially the gradual replacement of the GZ34 tube with the solid state rectification, used by Marshall a few months earlier on the 100 watts amplifiers.
The JTM50, in a very short time, underwent changes in look and function, including new bright caps for the Lead version, but especially the gradual replacement of the GZ34 tube with the solid state rectification, used by Marshall a few months earlier on the 100 watts amplifiers.
Towards the middle of '67 the labels “JTM50”, “MK II”, “High Treble”, “Normal”, present on the plexiglass front panel, were abandoned in favor of the simpler “J.T.M.” on a black background on the left hand side of the panel, from which the nickname “Black Flag” given to these amplifiers - and to a few 1967 100 watts Marshalls with the same label - comes from. To understand how slow the transition to solid-state rectification was, just consider that some Black Flags still featured the GZ34s.
Marshall 1987 lead, 50 watts, with black J.T.M. logo and devoid of MKII, High Treble and Normal labels, Courtesy of Amp Archives
In Autumn 1967, the aluminum chassis was replaced with steel, and in early 1968, the “JTM” label was replaced with “JMP”, which stood for “Jim Marshall Product”. Finally, in mid-1969, new aluminum front and rear panels, which were more robust and allowed for the use of new and more elegant serial numbers, replaced the Plexiglas ones, marking a sort of watershed for collectors, who began to divide Marshall amps into "Plexi" and "Metal" paneled.
Antonio Calvosa
