Replacement mini tone-pot for Super Pro

Dan Beller-McKenna · From: Durham, New Hampshire, USA

Anyone know where I could get a replacement? I removed mine when I acquired the guitar eight years ago. I'm moving away from using a matchbox, so I want the tone control now. The original toggle switch is fine, and I have a replacement .047 cap. But the original pot feels very flimsy and should be updated.

The one I acquired (in front here) doesn't fit through the hole in the endplate, which is a scant 6.2mm. The split end of the shaft (6mm) makes it, but the threaded part does not. The shaft on both of these is 18mm, or 11/16" long.

Any ideas? Thanks.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Do you not have room for a standard-size pot?
Does it mount on a metal or plastic plate? Thickness?
Can you enlarge the hole? (1/8" shaft pots are not common.)

Dan Beller-McKenna · From: Durham, New Hampshire, USA

Very little room for the pot; it sits right over the return springs ("over" with the guitar upside down, that is). I suppose one cut drill out the hole, but I wouldn't do that.

As it turned out, Bruce Derr, who was giving me some soldering pointers, had an old mini pot in his stash that was a good fit. Threads were just long enough to secure the pot. All fixed.

Patrick Fleming · From: South Dakota, USA

I wonder if Bruce has any more of them that he would be willing to part with, or where he found it. I have been looking for a replacement for nearly two years now....

Dan Beller-McKenna · From: Durham, New Hampshire, USA

Sadly, I doubt it, Patrick. He found it rummaging around a bin chock-full of old potentiometers. This one is probably as old as the steel itself. I saw some possible fits on mouser.com. They have about 10,000 different pots to sift through, though. I may go ahead and order a couple, they are super cheap, just to see if I can find one as a community service. If I do find a good one, I will buy 10 or 20 and have them for anyone who finds them self in the position Patrick and I were in.

Bruce Derr · From: Lee, New Hampshire, USA

Yep, Dan's right - it's a somewhat peculiar pot and there was only one in my "stash" that checked all the boxes. It's an old military type with a round body of about 1/2" diameter, a 1/4-28 bushing (I think it was 1/4" long), and a 1/8" shaft.

I poked around on Digikey and found a couple that might work.

- NTE Electronics part number 501-0096, $13.40. This looks very similar but the shaft is longer. Easy to cut, though.

- Precision Electronics RV6NAYSD504A, $21.78. This also looks very similar to the one we used.

- Bournes 3310P-001-504K, $3.10. This one has an even smaller body, only 9 mm square. But it has a plastic bushing and shaft. Cheap, though.

The issue that may affect all of these choices is the bushing length. The end plate is thick, and we only got one turn's purchase, more or less, when tightening the nut. I didn't measure the length of the bushing, or the thickness of the end plate. We just tried it, and it barely worked. We couldn't use the lock washer and we had to bend the little anti-rotation tabs out. The bushings on the choices above are all 1/4-32, a finer pitch than the old one I had, so that might allow an extra half turn or so. Considering the loose tolerances I've seen on some Sho-Buds, I imagine there is some variation in end plate thickness among the Super Pros out there. I recommend measuring the thickness on your guitar before ordering a pot.

The 1/2" diameter body on the pot we used was the absolute maximum diameter that would fit, and it's tight with those return springs vying for space. A 16mm diameter pot like the little CTS 270 series would be too large.

As for resistance value, the one we used was a 500 kilohm linear-taper pot. The original was 250 K. There's no problem with using a 500 K; it just gives you a little more isolation from the tone cap when the pot is at maximum (full treble).

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