Champion 600 Tube Chart On the inside of your vintage Fender amplifier there is a paper chart with the tube locations for that particular model. This is called the amp’s tube chart. On the tube chart there will be a rubber ink stamp with two letters. In the chart below you will see the letters that coincide with the year and month of the amps manufacture. The first letter is the year and the second letter is the month. For example CF would be 1953/June.

C 1953 A January
D 1954 B February
E 1955 C March
F 1956 D April
G 1957 E May
H 1958 F June
I 1959 G July
J 1960 H August
K 1961 J September
L 1962 K October
M 1963 L November
N 1964 M December
O 1965
P 1966
Q 1967
R 1968
S 1969

If the tube chart is not in the amp or has been torn or damaged and you cannot read the ink stamped letters you can date the amp by the codes on the potentiometers. Below is a chart of the manufacturing codes for potentiometers.

137xxx CTS
140xxx Clarostat
304xxx Stackpole
134xxx Centralab
381xxx Bourns

1 Meg Potentiometer

The first three digits are the manufacturer’s code. The last three digits are the date code. The fourth digit is the year of manufacture and the last two numbers will be the week of manufacture. So if the number on your potentiometer is 304728 it is decoded like this: 304 is the Stackpole manufacturer’s number, 7 means 1967 and 28 is the 28th week of 1967. Later potentiomters used a two digit year code making the number seven digits long. In this case the fourth and fifth digits are the year and the sixth and seventh digits are the week of manufacture. If you are unsure if the digit denoting the year is in which decade (1957, 1967, etc.) then try to determine this by the amplifier it is in. Tweed amps were made from the very early 1950’s through approximately 1960, blonde and brown amps were introduced around 1961 through 1965, blackface amps with black tolex started around 1964 through 1967 and silverface amps took over in 1968. These are rough guidelines to help date your amplifier. Remember that a potentiometer could have been replaced so it is always best to look at a few of them.

Credit: Ampwares and Jim Shine.