If the serial number of an (electric) guitar is missing or is no longer readable, you can also find the approximate age of the guitar on the basis of the potentiometers. On the potentiometer is a code that gives information about the manufacturer and the year and week when it is made. (EIA code)

Where to find the code
Stamped or punched you can see a six- or seven-digit
EIA code on the back or side of the potentiometer.
Sometimes there is a space or dash between the manufacturer code and the year/week code.

With the potentiometer decoder you can decipher when and by which
manufacturer it was made.

  Potentiometer decoder

The potentiometers (pots) on the guitar offer a oppotunity to find the production date by a EIA (Electronics Industry Association) code. Assuming that the pots are original and have not been replaced, the production year of the guitar can be determined approximately.

The EIA code on pots indicates the manufacturer and date when they are made.
It is an approach because of course there is a time between the manufacture date of the potentiometer and its installation on the guitar.

Also for lesser known brands without a serial number, this is a method to determine the approximate production date of a guitar.

Read EIA code
With help of the EIA number on the potmeter, the production date can be determined. The first 3 digits on a pot are the manufacturer code.
The last 3 or 4 digits are the date code.
With 3 digits, the first digit is the last digit of the year, and the last digit is the week number.
With 4 digits, the first 2 digits are the last 2 digits of the year.

IRC (International Resistive Company) used a different date code system.
Example: 2144190500k627 is produced in July (week 27), 1956.

Not all manufacturers have or use an EIA code on the potentiometers.
For some series of CTS potentiometers, the full code can be entered in
the decoder and, in addition to the production date, the specifications
are also deciphered. Example: 450GT79K504B2S1422
Serie: 450G Potmeter: 500 KΩ Tolerance: ± 20% Bushing Length: 19.1mm
Shaft Length: 28.6mm Torque: standaard  Gemaakt: May, 2014
Manufacturer: CTS (Chicago Telephone Supply)

Based on the production date of the potentiometer, you can determine the approximate year of construction of the guitar.
The potentiometers are of course produced earlier than the guitar, and
in addition that there always have supply in storage.
Therefore, approximately 6 months must be added to the production date, but it remains an estimate.

In the 1950s, Fender mainly used potentiometers from the Stackpole brand. From 1963, the switch was made to the CTS brand. To save costs, a huge stock of CTS was bought in 1966 that was installed on the guitars until 1971. Guitars made until 1971 can therefore have potentiometers with the datacode of 1966. To save costs, a huge stock of CTS was bought in 1966

The suppliers of pots at Gibson are (were) IRC,
CGE (with the Gibson logo), CTS and CentraLab.
IRC and CGE were used in the 1950s.
Due to a fragile construction of the CGE potmeters (show rapid wear over time), Gibson has therefore switched to pots from CTS and later on CentraLab.

Höfner guitars from before 1971 often do not have a serial number. You can read on the bottom of the pots of these guitars 128KΩ or 250KΩ with a 3-digit number. Here the first 2 digits are the week and the third digit is the year.

Potentiometer 1969, week 33

Often the EIA code cannot be read by the solder on the potentiometer. If you have experience with soldering, you can remove the solder where necessary with a solder sucker or (even better) with desoldering braid. If you have no experience or confidence, have someone do it for you.

Use a soldering iron of approx. 40 Watt or a soldering station set at approx. 700°F. / 370°C.
The soldering tip preferably of the chisel type, these are more efficient to transfer the heat than a pointed type.
Press the braid with the soldering iron on the tin that to be removed and wait until the braid absorbs the tin.

(Do not forget to solder the connections that have been removed again to the potentiometer.)