1966 White Panel Marshall JTM45 MKII / JTM50 EL34 transition model
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This is one very, very rare Marshall: it is one of the first transitional JTM45/JTM50's with EL34 power tubes as it still has the JTM45 MKII designations and a (lost) White Panel back panel, block ends aluminium chassis, solid state rectifier, 1202 118 power- and (replaced for period correct) 784 128 output transformer, NOS tubes all round. Restored to stock as close as possible, this is one hell of an amp that has the sweetest, creamiest ROAR!!
The Marshall JTM45 is the first guitar amplifier made by Marshall and possibly one of the most famous sounding amplifiers as it launched British Blues-Rock music in the 1960's.
The JTM45 was first handmade in 1963 in an all-aluminum chassis by Ken Bran, Dudley Craven and Ken Underwood. Because of its power, Marshall decided early on to build it as a head, with a separate 4×12 cabinet with Celestion speakers. The amplifier itself was based on the Fender Bassman. Early versions had used 6L6 or 5881 valves (a US version of the 6L6 in the output stage, later models used KT66 (from 1964), EL34 (from 1966), or KT88 (from 1967; in the 200W Major), and ECC83 (12AX7) valves in the pre-amplification stage.. Dudley was responsible for the changes from the Fender to what is now known as the JTM45.
Significant differences between the Bassman and the JTM include the all-aluminum chassis, a 12AX7 valve as the first in the chain (the Bassman has a 12AY7), the 4x12 Celestion speakers with a closed cabinet (compared to open-backed 4x10 Jensen speakers), and a modified negative feedback circuit which affects the harmonics produced by the amplifier. As Ken Bran later said, "The JTM also had different harmonic content, and this was due to the large amount of feedback that Dudley Craven had given it."
By the mid 1960s, the JTM45 had become so popular that it began to supplant the ubiquitous VOX amps, even their AC50, though it was just as powerful.
The JTM 45 became the basis for many subsequent Marshalls, most notably the Marshall 1962 combo, later referred to as the "Bluesbreaker" due to its use by Eric Clapton with John Mayall's Bluesbreakers.