Pot & Speaker Codes
& Patent Numbers
Electric guitars and amplifiers can be dated by the coded date located on either the potentiometer sides or back, or the rim of amplifier speakers. Patent numbers can also be used to help in instrument identification. They should be used in conjunction with other identifying factors such as serial and model numbers to help to correctly identify your instrument.
The source-date code is usually comprised of a 6 or 7 digit number. In a 6 digit code, the fourth digit indicates the last digit in the year of manufacture. In a 7 digit code, the fourth and fifth digits indicate the year of manufacture.
6 digit codes on pots were used up through 1960. In 1961 the 7 digit pattern came into existence. The last 2 digits tell us the week of the year that the item was made. Amp speakers tend to keep the 6 digit code after pot manufaturers made the switch to the 7 digit number. Sometimes there is a space after the first 3 digits, sometimes a hyphen.
A pot coded - 304420 - would have been made by Stackpole during the 20th week of 1954. A pot coded 1377429 would have been made by CTS during the 29th week of 1974.
If you have an instrument that you suspect predates WWII don't be alarmed if you can't use the pots to aid you in instrument identification. Codes on pots and speakers don't start appearing until after WWII.
Patent numbers can aid in dating an instrument by giving the earliest possible date that an instrument could have been patented.
Remember that a patent pending notice will pre-date a patent number. There is always lag time between when the patent is applied for and when it is actually granted. Because parts need to be used up, parts made during the patent pending time period, could have been used on instruments after the actual patent is granted.