- All vintage USA Big Muffs have source-date codes stamped on the underside of the potentiometer cans, or “pots”.
The pots are what the knobs are mounted to, essentally manually adjustable resisitors that control the voltage across a circuit.
These are codes often seen stamped on components found in US made vintage tube equipment.
This list is circa 1955, and some codes have been reassigned or added since that time.
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.
FIT'S A 16" BOTTOM BOUT GUITAR WITH A 3" THICKNESS AND A 41&1/2" LENGTH WITH NO PROBLEM. THIS 1960'S GRETSCH HARDSHELL CASE IS IN NICE SHAPE!
CASE IS IN NICE SHAPE FOR AGE, SOME TOLEX MISSING FROM SIDE, AND INNER LINING SHOWING A LITTLE PADDING, BUT ALL SOLID AND ALL LACTHES WORKING.
So a pot stamped 1377833 is a CTS pot made in the 33rd week of 1978.
Note that this does not mean a Muff with a 1978 pot was actually made in 1978, it just means it was not made much earlier than 1978.
Code formats were not completely standardized, but a little deciphering will generally yield the info of interest.