Early Marshall through the JCM800 series July of 1969 Marshall introduced the date coding system.Some of the older amps have an inspection sticker on the top of the chassis and they usually have the day, month and year the amp was made or inspected.
How to read the serial number (1969-1983) Marshall used a coding system that provided (a) model, (b) serial number, and (c) manufacture date.
This (a)(b)(c) sequence began in 1969 and was valid through 1983.
The reason for that is simple: Marshall amplifiers.
Marshall amps made it possible to get the sort of stadium-filling, high gain crunch we now associate with rock.
Does it have a serial number stamped on the chassis?
Marshall amps began featuring aluminum back panels in 1969.
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.
(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.