Since 1956, all Celestion chassis drivers have been stamped with a date code (two numbers and two letters), denoting exact date of manufacture.
The codes are added on the production line and are placed on the speaker's chassis leg, on the front gasket or on a label on the magnet edge.
The table below outlines the meaning of these letter codes.
Marshall amplifiers didn’t start using true serial numbers until July of 1969.
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1979-1981: Some Marshalls made from 1979 to 1981 have the serial number on the front panel.
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.
Marshall started using their four-digit model system around this time and most models should have this on the chassis.
Amps from this era are covered in black levant with a black front on heads or gray grille on combos, feature an old block-style Marshall logo, and all chassis' are mounted center.For example: S/L C 12357 S/L would indicate the model Super Lead 100 watt C indicates the year 1971 12357 is the serial number. Starting in 1993 until 1997 Marshall switched over to a new serial number system.