Dating marshall cabinet
Leading zeros are usually omitted from the day of the month, eg ‘6’ instead of ’06’.
From around Dec 1971 to Sept 1972 the day of the month is usually omitted: From around June 1976 the inspection letter is no longer included.
If you do ever find a letter ‘I’ in your Celestion date codes it is just a typo and should be a letter ‘J’.
Date codes are usually stamped on the front gasket of the speaker.
The date code is still on the front gasket but with a smaller font size.
Any greenback speakers with pre-April 1968 date codes printed on the chassis leg are likely to be fakes.
From around April 1990, the ‘T’ prefix is usually included with the model number.
However, I do not recommend using the stamp formats as the main basis for dating your speakers.
The problem is, Celestion were not very consistent with them and this confuses a lot of people: I have included the stamp formats in the year column headers on the chart if you want to use them.
The circular quality control stamp changes appearance through the years: From roughly March 1978 to mid 1980 – usually a large letter ‘P’ or ‘Q’.
From around mid 1980 to late 1985 – usually an “insp number” stamp with no circular border.