Looking for a pot for a lap steel

[Bob M.]

Hi All,
I'm looking to replace a bad pot that's functioning as a tone control in a very early fifties lap steel.
If someone can point me in the direction of some seller who might have this part, I would be grateful.

Here's the spec I need:
250K - Audio
1/2 watt
30% taper
solid shaft
long bushing

Most 250K-A pots I have found have a knurled split shaft and a shorter bushing, say for a Fender-like guitar. I need a long bushing that goes thru alot of wood on the face of this instrument, not unlike a Les Paul. The cool-looking original knob would like a solid shaft, if possible.

If anyone knows of a supplier who might carry this, I'd be grateful to hear about that. I've struck out at both Mojo and Mouser so far.

Thanks,
Bob M.

[stokes]

Try angela.com You say its acting like a tone control. Are you sure its not wired as a tone control?

[The Dude]

it might help to have some measurements and/or a picture. For instance "long shaft"- how long exactly? etc.

[Chuck H]

CTS makes a 250k "J taper" (30% audio taper). They also make long bushing pots for Les Paul guitars. As far as I know the resistance element is swappable in CTS pots.?. Unfortunately the long bushing Les Paul pots typically have a knurled shaft. But there are work arounds for that if you want to use a set screw knob. Basically, you're going to have to make a pot from parts and AFAIK CTS is the only brand that might make this possible.

[The Dude]

I'll add: Unless you're some sort of restoration purist, I don't think the 30% taper is a big deal. All manners of guitars use a regular audio taper pot for a tone control, and it works just fine. Hell, some guitar manufacturers use linear taper pots. It would likely be easier to find something that fits physical requirements if you didn't concern yourself too much with taper. Just my $.02.

[Chuck H]

Unfortunately the long bushing Les Paul pots typically have a knurled shaft. But there are work arounds for that if you want to use a set screw knob.

Just to clarify this, I usually just alight the set screw so it meets the slot for knobs that don't have numbers or a pointer. If I have to align numbers or a pointer I put a metal shim in the slot, the full width of the slot, so there's no flex when the set screw is tightened. You have to do this or half the shaft head WILL crack. The knob will run a little elliptical because the knurled shaft heads are slightly smaller than solid shafts. They sell brass rings that slip over the knurled head of the pot but I hardly see how that could be effective. Never made sense to me because it's not fixed to the shaft in any way and the ring isn't strong enough to protect the slot. Better to use a shim in the slot and accept the ellipse.

[Mick Bailey]

As far as I know the resistance element is swappable in CTS pots.?.

CTS wafers - and more often than not, wipers - swap quite neatly to effect a good repair and keep everything else original. They seem to have kept the same wafer size for ever.

Splined shafts can sometimes be too short and I machine a little extender out of 1/4" brass, faced off both ends and drilled to be a good tight fit over the splined section, then JB weld it in place. Sometimes the splines need reducing with a file or Dremel to allow for a greater wall thickness on the extension, but once fitted they never come off. In the days when I didn't have a lathe I used a pistol drill clamped in the vice between scraps of plywood. Holding the stub in the rotating chuck, I then used files and emery cloth to tidy things up. Centre the end of the rod with something pointed while its rotating, then use a drill bit held in mole grips to drill it out to the desired depth - starting with about 3/32 and then drilling out to the finished size. Doesn't take time at all.

[Bob M.]

Thanks for your comments.
Yes, it's a tone control. I was just alluding to that pots can be wired in different ways to accomplish different results, especially in lap steels.
I meant to say long bushing, not long shaft, like one finds on the pots of a Les Paul guitar, (I thought I did).
Yes, I know I can use a knurled split-shaft and make it work but in a perfect world, this pot would have a solid shaft.
I think taper is super important but then that depends how one uses a tone control. The instrument currently has a tone control with all the change from treble to bass bunched up in the final third of the pot's rotation, which is what I'd like to fix.
Anyway, there are alot of clever people here on this forum and I hoped someone would know of a supplier that had most of my spec requirements for this pot.

Yes, you can use electric guitar pots and wiring schemes and many lap steels will come out fine. But you can also stylize the parts to the instrument at hand and eek a little more performance out of the circuit to end up with a better result. I tend to see these lap instruments as their own animal.
Thanks again,
Bob M.

[Helmholtz]

They sell brass rings that slip over the knurled head of the pot but I hardly see how that could be effective. Never made sense to me because it's not fixed to the shaft in any way and the ring isn't strong enough to protect the slot. Better to use a shim in the slot and accept the ellipse.

With a shimmed slot the brass sleeve compensates the difference between shaft and pot hole diameter and thus avoids the "ellipse".

[Greg Robinson]

They sell brass rings that slip over the knurled head of the pot but I hardly see how that could be effective. Never made sense to me because it's not fixed to the shaft in any way and the ring isn't strong enough to protect the slot. Better to use a shim in the slot and accept the ellipse.

Those adapter bushings are meant to adapt 6mm T18 knurled shafts to 1/4" (6.35mm) solid shaft. You still need to put a shim in the slot - conveniently, the anti-rotation tab on the diecast bushing that's common on metric pots is just the right width - the brass adapter bushing is too thin to prevent cracking the split shaft.

The bushings won't fit over knurled 1/4" 24 tooth shafts.

EDIT: they'll also work on 6mm solid shafts of course, and then no concern about the split shaft snapping.

[Helmholtz]

The adapter bushings I know are slotted.
If not, cut them open to accept a somewhat larger shaft diameter.

[Greg Robinson]

The adapter bushings I know are slotted.
If not, cut them open to accept a somewhat larger shaft diameter.

Hmm, interesting. The ones I've always bought are a solid tube. I've tried slitting them to fit over a 1/4" knurled shaft, but they're then too thick to accept a 1/4" knob.
Not sure who the OEM is, but pretty sure they've always come from Allparts - I've bought them directly from Allparts, and a number of other resellers (here in Australia postage from Allparts is a killer on small orders, even with wholesale pricing).

What's your source Helmholtz?

[Helmholtz]

Sorry, don't remember. Got them decades ago here in Germany.

[Mick Bailey]

I meant to say long bushing, not long shaft, like one finds on the pots of a Les Paul guitar, (I thought I did).

I got that - but sometimes old 1/4" pots had a slightly longer shaft than modern pots, as well as a long bushing. It still remains to establish the brand of the original pot.