The first number is the decade:
5=designed in the 1950s
6=designed in the 1960s
The next character (letter) is the approximate year:
A=1951 (TV front tweed)
B=1952 (TV front tweed)
C=1953 (wide panel tweed)
D=1954 (wide panel tweed)
E=1955 to 1960 (narrow panel tweed)
F=1960 to 1963 (tolex era)
The number(s) after the letter is the model:
1=Champ 9=Tremolux
2=Princeton 10=Harvard
3=Deluxe 11=Vibrolux
4=Super 12=Concert
5=Pro 13=Vibrasonic
6=Bassman 14=Showman
7=Bandmaster 15=Reverb unit
8=Twin 16=Vibroverb
First Letter (year):
A = 1951 J = 1960
B = 1952 K = 1961
C = 1953 L = 1962
D = 1954 M = 1963
E = 1955 N = 1964
F = 1956 O = 1965 (black ink)
G = 1957 O = 1966 (green ink)
H = 1958 P = 1966
I = 1959 Q = 1967
Second Letter (month):
A = January G = July
B = February H = August
C = March I = September
D = April J = October
E = May K = November
F = June L = December
