The newest models are incredibly easy to date (read on, if you aren't already aware of the current serial numbering system) but dating older amps (pre-1993) are slightly more involved. Here's the story so far…  

July 1969 - September 1992  

In July of '69, Marshall introduced their first date code system. To determine the year of manufacture, a letter of the alphabet was included in the serial number. Here's how it works:

A – 1969/1970       C – 1971               D – 1972               E – 1973

F – 1974               G – 1975               H – 1976               J – 1977

K – 1978               L – 1979               M – 1980               N – 1981

P – 1982               R – 1983               S – 1984               T – 1985

U – 1986               V – 1987               W – 1988              X – 1989

Y – 1990                 Z – 1991/1992

“B” was skipped because “A” ran for 18 months and “I,” “O” and “Q” were also skipped because they looked too similar to numbers.

As a rule, the serial number is usually located on the back panel of the chassis but some amplifiers made between 1979 - 1980 had them on the front panel. Now, at this point you're probably wondering where exactly this letter can be found within the serial number. That's a very good question so here's the answer. From July 1969 to December 1983, the letter was put after the serial number. For example, let's say you found this stamped on the back panel:

SL/A  14532  D

What does it mean?  

SL/A = model number

12532 = serial number

D = Date code (1972)

From Jan 1984 to October 1992 however, the date code letter was before the serial number. For example:

S/A  F  14235

This time: S/A = model number    F = date code (1974) 14235 = serial number.

As already revealed in the two above examples, in the early days Jim also used a lettering system for determining the model of the amp. 

The codes used are as follows:

A/ - 200 Watt                                     SL/ or SL/A - 100 Watt Super Lead

SB/ or SB/A - 100 Watt Super Bass    SP/ - Super P.A.

ST/ or ST/A  -100 Watt Tremolo        S/ or S/A - 50 Watt

T/ or T/A - 50 Watt Tremolo              RI – Re issue                   

Interesting stuff and pretty easy too…learn it and you're bound to impress the folk in the stores with your vast knowledge! FYI, all the information you've just read (and more) can be found in our old pal Mike Doyle's excellent book, "The History of Marshall." This book is a great reference source so always keep your copy handy.  

1993 to 1997

Starting in 1993, Marshall switched over to yet another serial number system. This time they designated the year in which the amplifier was made in the first two digits of the number and the week of manufacture in the last two.

Examples:  

93877536: this tells us that the amp was made in week 36 of '93.

94923403: this tells us that the amp was made in week 03 of '94,  

1997 and on…

In 1997 Marshall changed to the latest dating system which is the easiest to decipher of them all. It is simply the year followed by the week.

Example:

1999-45-1234: this (surprise, surprise) tells us that the amp was built in week 45 of 1999…and yes, I do have a degree in rocket science in case you're wondering!