Post quem dating
Either term is also found followed by Latin ("not").An example is in the language dating method known as linguistic palaeontology.An archaeological example of a terminus ante quem would be deposits formed before or beneath a historically dateable event, such as a building foundation partly demolished to make way for the city wall known to be built in 650.
There may be "patterns" here and there, but nothing that one can rely on. The chassis, as mentioned, were then taken to Dartford, where the back panels were attached (the connectors soldered to the terminals in the amp), and the chassis screwed into the boxes that had been assigned. One can often get a good general sense of date from the type of box, whether or not the amp has a valve rectifier, and last but not least, from the two-letter date codes on the potentiometers: Serial number 1727.
Some of the pots are replacements, but the one indicated is original and bears the code "GL". The first letter is the month: "A" = January, and so on.
The second letter is the year: "K" = 1963, "L" = 1964, "M" = 1965.
The GZ34 valve was abandoned in favour of silicon diodes. Also worth mentioning, is the appearance of black-shrouded transformers at around serial number 5600 - an example above (no.
Solid state rectification - the AC50 mark 3 with brimistor The brimistor - a type of temperature dependent resistor designed to delay in-rush current and voltage - was marked as addition on schematic OS/072 (14th October 1965), and first appears in amps around serial no.