The Code on the tube chart of your Fender Amp is made up of two letters. The First letter equates to the Year and the Second letter to the Month. Reissue amps also use stamped Date Codes.
Examples of "Hand Stamped" Date Codes.
QA=Jan 1967
CG=Jul 1992 "Reissue"
*CAUTION* Hand stamped Date Codes and paper tube charts are "Easily" Faked. For a more Foolproof method of dating your amp, see Dating ANY Amp.