Marshall JTM100 Schematics
In 1965 the first (prototype and production) 100W amps (model 1959) were constructed using two 50W output transformers. Shortly later a single 100W output transformer was used. The first 100W Lead and Bass models used left over JTM45 panels (until some time in 1966), thus these amps were called JTM45/100. The 100W PA models did use JTM100 panels, as these amps sported 8 inputs instead of 4, requiring different panels anyway.
In the first half of 1967 the JTM panels were dropped all together and the JMP panels were introduced.
The early incarnations of the JTM100 amps varied in design. The JTM100’s were the first amps to use solid state rectifiers. A tube rectifier was just too much hassle and too expensive. The early 1967 JTM100s used a 3″ power transformer giving a B+ of around 560V. Due to a design mistake of Drake (the transformer supplier at that time) the US primary tap wasn’t correct, giving a dangerous B+ of around 640V in the US! Later in 1967 a smaller 2,5″ power transformer was used giving a B+ of around 460V.
Early JTM100s were fitted with KT66s. Later JTM100s were fitted with EL34s.
Schematically, all the JTM100s are all very similar. The PA version had 4 channels and 8 inputs instead of the usual 4 inputs and 2 channels, and a slightly different voicing.
JTM100 1959 Super Lead, 100W head
The Super Lead JTM100 was introduced in 1965.
JTM100 1959T Tremolo Super Lead, 100W head
The Tremolo version was an idea of Pete Townsend but it wasn’t very popular and not many of these amps were produced.
Schematic with 4x ECC83 & 4x KT66 (Marshall).
JTM100 1968 Super PA, 100W head
This amp had 4 channels and 8 inputs. It was the PA version of the 1959. The front panels were marked with MkV and JTM100. A lot (maybe all?) of the rear panels were marked with MkIII.
Photograph of a 1968 Super PA probably from 1966.
JTM100 1992 Super Bass, 100W head
This amp had 2 channels and 4 inputs. It was the Bass version of 1959.
JTM100 1992T Super Tremolo Bass, 100W head
This amp had 2 channels and 4 inputs. It was the Bass version of 1959T or the Tremolo version of the 1992…
1982, 4×12″ 100W cabinet
This cabinet was introduced in late 1966. It was the first 100W cabinet being fitted with four 12″ Celestion G12M-25 speakers. In the top left corner of the cabinet a ‘100W’ logo could be seen.