Newer amps are quite easy to date. Simply use the barcode.
|I I I I I II I I III
I I I II I
In the example above, the amp was produced in February (985555502) of 1998 (985555502).
Older amps are also fairly easy to date using the serial number.
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.
How to read the serial number (1984-1992)
In 1984, the order of the serial number components changed to (a)(c)(b), but the method used to determine the values for (a) and (c) remain the same. This system was used until 1992, when the bar code system was introduced.
a) Model - The first part of the serial number grouping determines the model of the chassis. Possible values are shown in the table below.
|A/ or /A||200 Watt|
|S/ or S/A||50 Watt|
|SB/ or SB/A||Super Bass - 100 Watt|
|SL/ or SL/A||Super Lead - 100 Watt|
|ST/ or ST/A||Tremolo - 100 Watt|
|T/ or T/A||Tremolo - 50 Watt|
(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. Since A was used in both 1969 and 1970, Marshall decided that 1971 would start with C. To avoid confusion with the numerals 1 and 0, Marshall elected to skip the letters I and O. Also, for reasons not explained, there are no Q-dated amps. Z was used for two years.