Walk into any vintage guitar control cavity—especially anything mid-century American—and there’s a good chance you’ll meet three little stamped digits that quietly tell a huge story: 137. That’s the maker’s code for CTS, one of the most important behind-the-scenes companies in the electric guitar era.
CTS didn’t build guitars. But CTS helped define how guitars feel, how they respond, how they get louder, and how we date and authenticate the instruments we love.
The company before the guitar: Chicago Telephone Supply to modern CTS
CTS began life in 1896 as Chicago Telephone Supply Company, originally focused on the early telephone boom—building the kinds of components that made mass communication possible. Over time, the business evolved far beyond telephony into a broad electronics manufacturer (today spanning sensors, actuators, connectivity and electronic components for multiple industries).
That background matters: the skill set required for reliable, repeatable component manufacturing—tight tolerances, durable materials, consistent output at scale—is exactly what later made CTS such a natural fit for the post-war electric instrument explosion.
Why potentiometers mattered so much in the electric guitar boom
A potentiometer (pot) is basically a variable resistor—in a guitar it’s most commonly your volume and tone control. Pots look simple, but they sit right at the intersection of:
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Player feel (how smoothly the knob turns; how the taper behaves)
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Circuit behaviour (how a pickup is loaded; where treble rolls off; how quickly a volume control “cleans up”)
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Factory consistency (whether 10,000 instruments behave similarly)
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Reliability (scratchy controls, dead spots, drift over decades)
As electric guitars became mainstream in the 1950s and 1960s, makers needed parts they could buy in large volumes that stayed stable on a production line. That’s the world CTS came from.
The “CTS effect”: how their pots influenced guitar tone and control response
1) Consistency helped standardise what “normal” guitar controls feel like
A big part of why classic guitars feel familiar is that their electronic components became repeatable. CTS pots were widely used across American instruments, helping standardise control layouts and behaviours across models and brands (and across decades).
2) Pot values helped define brightness, thickness, and headroom
The value of a pot (measured in ohms—commonly 250k, 500k, 1M) changes how much the pickups are loaded:
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Lower values generally shave off some high end (often perceived as warmer/smoother).
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Higher values generally preserve more brightness and bite.
This is one reason certain model “families” became associated with particular tonal profiles over the decades. CTS didn’t invent those musical preferences—but their mass availability helped make them repeatable in production, and therefore repeatable in recorded music.
3) Taper choices shaped the famous “volume roll-off” behaviours players rely on
Whether a pot is audio/log taper or linear taper affects how quickly the sound changes as you rotate the knob. That seemingly small detail is the difference between:
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a volume control that cleans up gradually and musically, versus
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one that feels like “nothing happens until 7, then everything happens at once.”
A lot of player technique—especially riding the guitar volume into a cooking amp—depends on this. It’s part circuit, part component choice, part tolerance reality.
4) Reliability became part of the vintage story
CTS pots earned a reputation for durability, which is why they show up in so many surviving guitars—and why they became part of the vintage authentication toolkit.
CTS and the vintage detective’s best friend: the pot code
CTS pots are famous among collectors because they often carry an EIA manufacturer/date code stamped into the casing. In many cases, it’s the most reliable breadcrumb you’ll find without removing a neck or pulling pickups.
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137 = CTS (manufacturer ID)
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The following digits typically encode year and week of manufacture (format varies by era).
Example: a code like 1377624 is commonly read as CTS, 1976, week 24.
Why this matters for dating guitars (and what it doesn’t prove)
Pot codes can give you a “not earlier than” date for the instrument—because the guitar can’t have been assembled before the newest component inside it was manufactured. But there are caveats:
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Pots can be replaced (especially if scratchy or failing).
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Factories sometimes used parts that sat in bins for months.
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Solder joints, wiring style, and overall wear patterns still matter.
So: pot codes are powerful evidence, but not a magic birth certificate.
CTS in context: the big three American pot codes you’ll see
When you’re poking around a control cavity, the three codes that come up again and again on classic US instruments are:
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137 = CTS
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134 = Centralab
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304 = Stackpole
That short list tells you how concentrated the supply chain was—especially during the golden years of American electric instrument production.
How CTS helped shape the “classic wiring era”
Think about the iconic control schemes that became templates for generations:
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Volume + tone simplicity on bolt-neck classics
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Independent volume controls and interactive tone networks on set-neck favourites
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The gradual evolution of treble bleed mods, cap choices, brighter/darker factory voicings
All of those worlds depend on potentiometers behaving predictably. CTS pots became part of the invisible infrastructure that allowed manufacturers—and then modders and techs—to build a shared language of what a guitar control circuit is “supposed” to do.
Why this still matters today (even if you never buy a vintage guitar)
Even in 2026, CTS is relevant for players because pots are one of the easiest ways to change how a guitar responds without touching pickups:
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Want a touch more bite and openness? A different pot value can help.
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Want volume cleanup that feels more controllable? Taper matters.
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Want a touring guitar that stays consistent night after night? Build quality matters.
And if you do buy vintage (or vintage-style), CTS pot codes remain one of the quickest ways to sanity-check a story.
A quick takeaway for buyers and builders
f you’re inspecting a guitar and you see 137 on the pots, you’re looking at a component from one of the most historically significant suppliers in the electric guitar ecosystem. It doesn’t automatically mean “original,” and it doesn’t automatically mean “better,” but it does mean you’ve found a valuable clue—one that links your instrument to a supply chain that helped define the sound and feel of electric guitars for decades.
