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Home : Trade Secrets Archive : Issue 150, Fixing dirty, scratchy control pots on a Supro lap steel
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Image: service station DanPit stop at Dan’s shop:
Fixing dirty, scratchy
controls on this 1960
Supro lap steel

Dan Erlewine, October 13, 2011
Photo: Supro lap steel My friend Spencer Bohren is a traveling blues man from New Orleans. We have a deal: when he comes through Ohio, I fix his guitars and he teaches me old style blues.
Spencer was here last week with an ailing lap steel: a Supro Jet Airliner model from 1960. Here’s what he said:
“These control pots are scratchy and hard to turn, and the tone is lackluster. Can you can fix them without changing the vintage parts?”
The way Spencer got this guitar is a good story:
“After Hurricane Katrina, the Cleveland Blues Society wanted to give me a guitar to replace one I lost in the storm. What I needed more was a gig, so I could buy $700 worth of drywall for my flood-damaged house. I played Cleveland, and was headed home with $1000 in my pocket when I saw this old steel in the corner of a music store.
The salesman didn’t think it would play, but I plugged it in and it was sensational! He liked my music and sold me the steel and everything else I needed for $300. This way, the Blues Society got me a guitar after all and my house got the sheetrock. Everybody was happy!”

Photo: Dan unpacking Spencer brought this to the right guy. I love Supro lap steels. Are they “art deco” style? I'm not sure, but they look great!
The pickup lead wires were so short that there was no slack to turn over the pickguard for access to the controls. This meant I had to remove the pickguard.
Off came the metal bridge/pickup cover, which was held with rusted screws (photos 1, 2, 3, 4). I used needlenose pliers with leather padding to turn the rusted parts, then cleaned them with a mix of naphtha and Tri-Flow oil. Oil-and-naphtha is my all-purpose rusty parts solution.
The knobs were fixed to the control pot shafts with set screws, but they were on tight. I gently lifted them off with a knob puller (pics 5 & 6).
Photos: parts cleaning
Behlen Naphtha


Tri-Flow


Knob and Bushing Puller
Photo: removing the hex nut A T-handled nut driver (1/2") removed the hex nuts on the pots and the output jack.
Guitar Nutdrivers
Photo: control cavity Inside, the control cavity was clean as a whistle. Sort of surprising that the control pots were dirty, but you never can tell...
Photo: broken capacitor Aha! There is more of a problem than dirty pots: one leg of this old capacitor was broken clean off. This is a pretty easy fix. Normally, I like to use one of our modern replacement caps; I believe they hold up to soldering temperatures better than these old ones.
Capacitors
Photo: replacement capacitor But Spencer asked for no new parts. After some rummaging around, I turned up an old cap that’ll do the trick. (Spencer will never know the difference!)
See bigger photos on our Facebook page
Photo: heat-shrink tubing Heat-shrink tubing on the leads from the replacement cap guaranteed that they wouldn’t short to the ground wire.
Heat-shrink tubing
Photo: spray cleaner I cleaned both pots with DeoxIT contact cleaner and put the Supro back together. I looked up the codes on the pots, and they dated this guitar to 1960. 
DeoxIT Pot & Switch Cleaner
Photo: multimeter Everything’s back together and sounding good. The pickup output reads around 5.8k on my multimeter. This Supro’s ready for Spencer.
Portable Digital Multimeter
Photo: Dan & Spencer And he’s happy! Me too, because we spent some time playing blues. We were in the mood for country blues, because Spencer recently released the CD, Blues According To Hank Williams. I love hearing him play the old Don Helms and Jerry Byrd stuff. You can see Spencer playing this very lap steel on Youtube: search for “Spencer Bohren steel jam.”
Problem-solving products for this kind of work:
Behlen Naphtha Solvent
General purpose cleaner that's useful in all aspects of instrument repair.
DeoxIT Pot & Switch Cleaner
One-step spray for cleaning and quieting noisy pots and switches in guitars and amps.
Tri-Flow
Luthiers' favorite for lubricating tuners, tools and metal guitar hardware.
More More More
Guitar Nutdrivers
No more fumbling through your socket set for the right wrench!
Guitar Tech Screwdriver Set
36-piece compact tool kit just for fretted instruments. A StewMac exclusive.
Portable Digital Multimeter
Test continuity, AC/DC voltages, amperage, and ohm resistance of pots and pickups.
More More More

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