Fender tube chart decoder

Between 1950 and 1970 Fender pasted a tube location chart inside the cabinets of most of its amps: a printed sticker with the valve layout and a small date code of two letters. The first letter is the year and the second is the month, so FG reads as July 1956.

The vintage cycle runs from 1951 to 1969 across the letters A to S. Fender reissued many of these designs from 1990 and the reissue charts use the same alphabet again, so CG is July 1953 in one column and July 1992 in the other. Without the second column a reissue reads as a 1950s amplifier.

A tube chart dates the cabinet batch rather than the finished amp, and charts were printed in runs and occasionally used on a model they did not belong to. Some amps carry no chart at all, and in January and February 1966 the printing left OA and OB where PA and PB belong.

Where the chart survives it is the strongest single witness these amps carry, and it is the one witness that gives a month rather than a year.