There are a number of resources available online to help you to date your guitar amplifier or bass amp.
Many of these resources refer to source-date-codes located on pots or speakers within your amplifier.
So, always keep your eyes open for “fishy” deals, look for information, and always ask for high definition photos (especially from the interior of the amps – the circuit, the tubes and transformers) to make sure everything is right.
The final line contains a date code of two printed or handwritten letters denoting the amplifier’s production date by year (the first letter) and month (the second letter).
Before starting, I must warn you that acquiring vintage gear can be really risky.
Non-Schumacher transformers – It’s been universally accepted that Fender only used Schumacher transformers on amps made in the 1960s and 1970s.
These are marked with EIA code “606” which is the company number for Schumacher.