Dating by pots
Electric guitars are full of dated parts. The one most people can read without special tools is the potentiometer, the volume or tone control. Each carries a short stamped number that names its maker and the week it was made.
Finding the code
Open the control cavity or the back of the control plate, or look at the body of the pot from underneath. The code is stamped on the metal case, often beside the resistance value. You need good light and sometimes a magnifier. Do not unsolder anything to read it, and do not force a control plate on an old instrument. If you cannot see it without damage, leave it.
Reading the code
The code is the EIA source code convention: a three-digit manufacturer code, then the year, then the week.
- Six digits: manufacturer, one year digit, two week digits. The decade is not stored, so 137 2 05 could be 1952, 1962 or 1972. Use the era of the instrument to choose.
- Seven digits: manufacturer, two year digits, two week digits. 137 52 05 reads as maker 137, 1952, week 5.
The week must be between 1 and 53. The pot code decoder rejects anything else, and lists every year the six-digit form allows.
Makers on the list
The table on the pot page covers CTS (137), Centralab (304), Stackpole (134), Clarostat (140) and Switchcraft (328). CTS and Centralab are the codes collectors most often report. The other three are reported by collectors and not yet checked against the EIA list. The list is a partial subset, so a code outside it is reported as an unlisted maker code and the year is still read. See the About page for the known gaps in this list.
What a pot code proves
It proves the pot was made in that week, which means the instrument cannot have been assembled before it. It does not prove the guitar was built in that week. Makers stocked pots for months and sometimes years, and used them in the order that suited the shop. So read it as a floor.
That floor is useful. If a guitar’s serial reads as 1958 to 1962 and the pot is stamped 1960, the guitar is not from 1958 or 1959. The decoder does this for you: enter a pot code beside the serial and any reading that ends before the pot floor is ruled out, with the reason shown.
What a pot code cannot prove
A replaced pot. Controls fail and get swapped. A late code on an otherwise early instrument suggests a repair. A mix of pot ages on one guitar is more often a sign of repair than a sign of mixed stock, and the oldest code is the useful one only when you believe the pot is original. Look for signs: fresh solder, mismatched shaft finish, or one pot in a different style.
Reading several pots
Check all the controls and write each code down. If they cluster within a few weeks, that is reassuring. If one is years later, it is probably a replacement. The earliest of the cluster sets the floor. The decoder takes the minimum year candidate from whatever you enter, so enter the earliest code you trust.
Putting it with other clues
Pots work best alongside the serial and a physical feature. A Gibson with a “Patent Applied For” pickup sticker, a pot dated 1959 and a serial in a likely 1958 to 1961 band forms a consistent set. A Fender neck plate, a heel date and a pot all pointing to the same year is stronger still. Where they disagree, say so in your notes.
Check this next
Enter the earliest pot code you trust in the decoder’s pot field and see which readings drop out. Then confirm the remaining ones against one feature on the timeline.
A pot is a clue to the earliest date, never a verdict. Nothing here values or authenticates an instrument.