I won’t write the rest because it may confuse you even more. It’s important to note that, for example, a 1959 amp has nothing to do with the The JTM-45 JTM-45 with “block” logo The first Marshall ever made. The front panel has “Presence”, “Bass”, “Middle” and “Treble” controls, as well as 2 volumes and 4 inputs.
To avoid confusion with the numerals 1 and 0, Marshall elected to skip the letters I and O.
(a) Model - The first part of the serial number grouping determines the model of the chassis. (b) Serial number - The second part of the alphanumeric grouping is the five-digit serial number itself.
(c) Manufacture date - The last character determines the date of manufacture.
Also, for reasons not explained, there are no Q-dated amps.
Z was used for two years, allowing time to convert to the bar coding scheme started in October 1992.
Eric Clapton used a JTM-45 combo on the legendary (Now you know why this amp was called “Bluesbreaker” : P) He used his Les Paul through the Normal Channel of the amp. The then “horrible” distorted and saturated sound turned into what we know today as the “rock tone” (maybe not yet… Another example of this amp can be heard on AC/DC’s This is a confusing era, with lots of changes and new models. 😛 The transitition from the JTM to the JMP amps happened, in my view, with three steps.