Fender circuit codes

Fender circuit codes appear on schematics, tube charts and paperwork: two letters, then digits, with a suffix on some revisions.

The letters mark the revision and the digits the drawing, which is how AB763 is documented in July 1963. Fender then built the same circuit for years, so the code cannot date an individual amplifier.

The canon data holds 59 of these codes as era markers from the early 1960s onward, and uses them for what they are: a way to place an amp in a generation of designs rather than in a month.