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Many very qualified and well-educated collectors and dealers say that in today’s vintage guitar market, you have to accept that things get changed along the way when it comes to worn-out electronic parts. It is just a reality, like a Stradivarius violin needing a neck rebuild, fingerboard level, or top or back removal over time.
That’s all true, but when it comes to manufacturing potentiometers, most of today’s materials are subpar compared to the virtually unbreakable materials of yesteryear. This is certainly true when it comes to guitar electronics. Have you ever noticed how often you might replace the pots on your main guitar from the ’70s or ’80s, or how your newer guitar can lie in its case for a few months and when you go to play it, the volume pots are scratchy and won’t even clean up with proper cleaner?
Vintage guitars from the ’50s and ’60s have some of the best-built potentiometers ever. These pots featured heavy carbon-resistance material instead of the inferior silk-screening currently used by many of today’s makers. These old-school materials rarely wear out. If there’s a problem, it’s usually caused by corrosion on the wipers or brushes, solder bleed, or tainted substances that find their way onto the resistive material. For the most part, this is all restorable.
When the original pot was removed from the show-and-tell ’54 Les Paul, fortunately the owner placed it inside the case’s compartment. I couldn’t have been more pleased to find this, and I was certainly up for a challenge in restoring this 1954 pot.
IRC (International Resistive Company) pots were used on many Gibson Les Pauls. Today, IRC provides one of the industry’s most comprehensive ranges of innovative resistor solutions for automotive, computer, communications, medical, industrial, military, and instrumentation markets worldwide.
Left: Measuring the potentiometer’s resistance with a digital multimeter.
Right: Carefully prying open the pot’s chassis-support tabs.
I began restoring this vintage IRC pot by using my portable digital multimeter to read the pot’s resistance in ohms (Photo 1). The brass shaft section of the pot was locked in open position, and it would not rotate. In open position, the resistance read 550 kΩ— despite the fact that the pot’s chassis was stamped 500 kΩ. On the side, another group of numbers indicates the year of manufacture (you’ll need a source-date code system to interpret them).
Consider this: In pursuing ultimate tone, if we’re really stuck on the accuracy of a 500 kΩ pot, we have to be aware of some serious variability going on here. The IRC pot I was restoring reads 550, yet I can buy a bag of modern pots and most of those will read under 500 kΩ, at times even as low as 450 kΩ. That’s a potential 100 kΩ difference between the two. Wow—isn’t that an eye-opener? It’s a good idea to always use a meter and select your pots accordingly.
My next step was to use an angle vise (which works well because it has some girth) to hold the pot as I tried to manipulate its shaft (Photo 2). Unfortunately, the pot’s durable brass shaft wouldn’t budge loose—it was as if it was once glued into position. This meant it was time to investigate inside.
Notice how I attached two maple strips to the vise jaws to support the pot and protect it from scratches or damage. I used a mini screwdriver that’s slightly narrower than the chassis- support tabs to bend them open. The size is important, because later when everything is reassembled, any micro pressure marks will be hidden under those four tabs. This creates an invisible restoration.
We’ll conclude our pot-restoration project next month and list the tools you need for this work, so be sure to swing by for the second installment.
John Brown is the inventor of the Fretted/Less bass. He owns and operates Brown’s Guitar Factory, a guitar manufacturing, repair, and restoration facility staffed by a team of talented luthiers. His guitar-tool and accessory designs are used by builders all over the world. Visit brownsguitarfactory.com or email John at firstname.lastname@example.org.