If the pot is an original, it indicates a date before which the guitar could not have been built – so it’s always a good idea to have extra reference material around.Finally, a word of caution: This method applies only to American made pots and not all potentiometer manufacturers subscribed to the EIA source code date.
The EIA assigns each manufacturer a three-digit code (there are some with one, two or four digits).
When dating an instrument by the ‘pot code,’ keep two things in mind: The potentiometers must be original to the piece (new solder, or a date code that is off by ten or more years is a good giveaway to spot replacement pots); and the pot code only indicates when the potentiometer was manufactured!
Then 134-6320 would become 134-320 and the specifications of the instrument should be used for determining the approximate year or decade the particular instrument was built.
Here is a brief listing of the manufacturers Source Code numbers: 34 – Cornell-Dubilier Electronics (made capacitors used on early Fender Guitars and are the ones that were paper and wax coated.
This can be done by adding, following a hyphen (-), the last two digits of the production year plus the number of the week of that year.
Here is hypothetical example of the application of the EIA date code to the source code as follows: A company is assigned the source code symbol 134 (which is for the potentiometer manufacturer Centra Lab).
In the second string of numbers, the first three numbers are a code identifying the manufacturer.
The next two numbers after the manufacturer number are the year, and the last two numbers are the week of the year the pots were made.
If the code does not fit the above criteria, don’t force it and skew your dating results.
Part Number: 137-8916 10k Date Code: AH9715 Manufacturer: CTS This 10 turn “BALL POT” 10K Ohm panel mount Potentiometer has a 1/4″ diameter shaft 3/8″ long with a threaded bushing 3/8-32 thread 3/8″ long and wire solder terminals for instrumentation controls. The multi-turn feature allows for accurate setting of the Potentiometer.
This should never be the only method used, but quite often it can help back up evidence already acquired to date an instrument. First you need to get underneath, to the circular disc on the bottom of the shaft at the opposite end of the knob (which may, or may not, have to be removed depending on the instrument).