Vintage CTS Pot Question From a Plexi Marshall

[Guitarman18]

I've been trying to trouble shoot a '69 Plexi Marshall, that has been producing scratchy frying bacon sounds and after re-flowing the solder on the volume pot noticed that it improved it a great deal. However, it wasn't the new solder that helped, it was the pressure on the middle lug of the pot that had moved.
Turns out that as you sweep the pot, the middle lug rocks (not Rocks!) backwards and forwards. I've removed the pot and dismantled it, but I would like to restore it rather than just replace it with a modern equivalent.

My question is; how does the inner (pin 2) brass lug ring need to crimped (?) in order for it to sit securely in place?

Any advice would be greatly appreciated, as always.

Cheers,

Paul.

[Reeltarded]

Look at you! Trailblazer!!

Kidding. Never had one apart that far. The spacers under the mounting plate don't handle that?

[telentubes]

The correct spelling is "Rawks!"

[Structo]

The carbon trace looks pretty trashed so you might be better off replacing the pot.
The middle lug is the wiper on the trace.

Sure the newer pots don't have the same taper but it will just change where the knob is pointed although the purists will say you have to have a 30% taper for it to work right.

[Reeltarded]

Using a tiny screwdriver, bend the feet outward onto the unworn trace areas.

Put it back together and if it works.. fergit aboot it.

[Leo_Gnardo]

Might also try gently polishing both the metal ring and carbon track with super-fine (sand)paper @ 1200 to 2000 grit, then follow up with a drop of 5% Caig Deoxit and wipe clean with a cotton bud (Q-tip). If Deoxit (F5 or D5) not available, any competent pot-cleaner will do. And as Miles said, very gently bend the metal "brushes" sidewards so they will be riding unworn/less-worn carbon track.

If that doesn't work, a replacement is needed. If a new pot happens to be internally identical you may be able to swap in a new wafer-with-carbon-track, and no one will be the wiser.

[Guitarman18]

Thanks for the replies.

I had to give it go. The pot, as it was, was not working properly so I had nothing to lose.

Having made my original post I did some thinking and realised that the only thing that would have been moved on the pot (apart from ware!) would be the lugs. The middle (brass) one in particular, close to the solder lug, has three 90 deg. folds that wrap the board that supports the trace. I realised that someone had bent the middle pin to such an extent that that the brass had slightly flattened out. Once I set the angles correctly again it snapped nice and snugly into place! See picture below.

I cleaned off the trace with a cotton wool bud and contact cleaner and it came up pretty clean. The tracks in the trace were from the grease that has been deposited on the trace. Now it is hard to see any ware on the trace. Having said that, the trace is so thick the wiper could have probably dug a channel 1mm deep and it would still work! (OK, maybe not!)

I reassembled it, put it back in and it works beautifully.

I did consider looking at Leo_Gnarno's suggestion before I started working on it and using a trace from another pot, but once cleaned up, I realised I didn't need to do that.

So, as it turns out, it wasn't as bad as I first thought! I'd recommend giving it a go to anyone face with the same situation. I feel as though I've saved something for posterity.

Thanks once again to everyone for their suggestions.

Best wishes,

Paul.