Potentiometers are a critical component within the circuit of an electric guitar or bass. They are also known as variable resistors, and in the context of electric guitars, they are generally used to control the volume and tone of the instrument. A potentiometer typically consists of a resistive element, a wiper (a movable contact), and two terminals. The resistive element is usually a coiled wire wound around an insulating core. The wiper, connected to the guitar’s control knob, moves along this resistive element, altering the amount of resistance in the circuit as it turns. This change in resistance, in turn, affects the flow of electrical current and, subsequently, the guitar’s output.

In vintage electric guitars, potentiometers are primarily used for volume and tone control. The volume pot allows the player to adjust the output level of the guitar, from a whisper to a thunderous roar. However, it’s the tone pot that truly alters the sound of an electric guitar or bass. This simple knob provides a gateway to an array of tonal possibilities, from warm, lower-end tones to biting bright and trebly sounds.

Aside from their function within an electric guitar’s circuit, pots also serve as a key element in dating a vintage instrument. Which is why it’s crucial to understand what to look for when opening up and examining a guitar or bass. More often than not, pots in an instrument manufactured in the 50’s or 60’s have been replaced. This directly impacts the value of the instrument. In some cases, only one could be changed, and in other cases an entire wiring harness could’ve been swapped out or “upgraded” as was common before preserving originality was of utmost importance. For this reason, pots are only one of several potential clues one can use in dating an instrument. While it may not tell you everything you’d like to know, dating pots can be a useful tool that indicates whether a particular instrument is completely untouched, or if there’s been someone “under the hood” since it left the factory.

The potentiometers used in vintage electric guitars can vary in their electrical characteristics. The most common types are audio taper (logarithmic) and linear taper. Audio taper pots are the standard choice for tone controls because they provide a more even and natural sweep of tonal changes as the knob is turned. Linear taper pots, on the other hand, have a linear change in resistance and are typically used for volume control.

Additionally, vintage guitars may feature different potentiometer values (measured in ohms), such as 250k, 500k, and 1Meg. The choice of potentiometer value can significantly impact the guitar’s tone. Lower values like 250k were most often used in single-coil pickups to tame the high frequencies and produce a smoother, more rounded tone. This is almost always what you should see in a vintage Fender equipped with it’s original single-coils. Higher values like 500k are common in guitars with humbuckers, as they allow more high frequencies to pass through, resulting in a brighter and more aggressive sound. 500k pots are most often found in Gibson guitars, as they originally developed the humbucker in 1956 and used these pots accordingly. Many other American brands have used either 250k or 500k pots such as Gretsch, Guild, Rickenbacker, Epiphone, Magnatone, Harmony and so on.

In those days, most companies in the United States turned to the same few electronics manufacturers to supply their companies with pots and for building guitars, basses, amps and so on. These American manufacturers each had their own respective codes that were stamped onto the pots directly, usually found on the bottom or on the side or the pot. While there is a general “rule” to reading pot codes, you may at one point come across something that doesn’t follow the familiar format. But you will likely be able to discern where a year, manufacturer code, or resistance value may be found.

Gibson primarily used two manufacturers as their potentiometer supplier. CTS and Centralab. These two companies share similar three-digit codes, 137 for CTS and 134 for Centralab. Fender also used CTS and Centralab, but they also used a third supplier, a company named Stackpole whose manufacture code is 304 respectively.

Generally, when observing a 7-digit number stamped on the pot, the first three digits indicate the manufacturer of origin. The following two digits represent the year, and the last two the week of that year. Let’s take a look at this 1975 Sunburst Stratocaster for example.

We can see there are two sets of numbers. What gives?! Well, the numbers starting with 035 are Fender’s part number, and doesn’t help us uncover anything substantial about date. The other set of numbers is what we’re looking for. We can see the number beginning with 137, which tells us that they are CTS pots. Now we have a 75, the year of manufacture. And finally, a 17, meaning the 17th week. With 52 weeks in a year, we can assume this pot was made around late April or early May of 1975. These are some of the details we’re looking for when examining a vintage guitar. When using the other sources of dating info, as well as some visual clues in the wiring, we can now declare these pots being 100% original to the guitar.

You may also run into codes that don’t follow the exact same system as mentioned above. One common example is a 6-digit code. While these numbers generally still tell us the same information, it takes a bit of extra detective work to uncover the year. A 6-digit code will usually indicate only the last number of the year of manufacturer.

In this example above, we can recognize a harness from a vintage Fender guitar. 304 tells us that its Stackpole, but with only 3 remaining letters, we cannot assume that the following 2 digits represent the year. That would imply that these pots are from 1992. These are certainly not 90’s pots, don’t make this mistake!

Instead, the number following the manufacture code is the second number of the year. This could mean the pots are from 1959, 1969, or 1979. This is where it takes some expert knowledge to narrow down the possibilities. This is a 50’s harness, so it’s safe now to assume that these pots are made around June, 1959.

While dating pots is in an important tool in gathering information about a particular guitar, it’s not everything! If you’re looking for an appraisal on your guitar’s value, or are looking to sell a guitar but are unsure what else you need to know beforehand, contact us here

Potentiometers are the unsung heroes of vintage electric guitars, providing the means to shape and refine their iconic tones. They also serve as one of many tools to uncovering a vintage instrument’s history which is why learning how to read codes and stay informed is ever so important when buying or selling any vintage guitar, bass, or amplifier.