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Rheostat reconditioning

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Sceadwian

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Taking out the garbage today I happend across a junked speaker cabinet, it was trashed but I snagged the voice coils out of a decent woofer and tweeter to play with, it also had a crude crossover for the tweeter consisting of a 10u 50V capacitor and a 25ohm wirewound rheostat. Judging by the size I think it's rated for approximatly 25 watts.

I googled the markings on the rheostat but came up with zip,
They are
CM39771
25Ω
20-7311

If it rings a bell to anyone but I'm not worried about the wattage specifics. I popped the top off the sucker cause I've never seen the internals on a large rheostat before, and it's quiet neat and tidy. It is showing a little bit of corrosion though, primarily at the contacts, the motion is still smooth as glass but when connected to my multimeter it was going high limit briefly during rotation so I'm guessing the corrosion is enough that it's making bad contact a bit. I was planning on using vinegar to clean some of the oxide off and then follow up with a good flush with rubbing alcohol to try to clean the contacts up a bit, but what would I be able to put on afterwards to help protect against corrosion but not screw with the electrical side of things? I was thinking oil but it's too good an insulator, and I'm not sure if the contact pressure would be enough to displace a thin oil coating. Is there anything that would work? Or would I just be better off cleaning the crap out of it and buttoning it up again relying on isolation to keep it from corroding?
 
The do sell contact cleaner in electronic stores. I don't know what's in them, but that's probably the best thing to clean the contacts.

Don't know of anything you can put on the contacts to protect them that isn't an insulator
 
Yeah I've seen that stuff before, always been wary though simply because I don't know what's in them, I doubt they're meant for something like the internals of a wirewound pot, the lines are too close together.
 
I would use volume control spray cleaner. It removes oxidant damage and leaves a light lubricant.
What am I missing?

In the old days, there was a goupy spray you could shoot into TV channel rotary drum tuners.
Sometimes we used a light coat of Vaseline. It worked...I don't know how long.
 
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flat5, this is a power rheostat, not a low current POT, as I said previously it's power rating is in the neighborhood of 25watts.
 
I would clean it up as you mentioned:

I was planning on using vinegar to clean some of the oxide off and then follow up with a good flush with rubbing alcohol to try to clean the contacts up a bit

Then if you are worried about oxidation I would follow up with a silicon spray that should inhibit oxidation and future corrosion. There are cleaners **broken link removed** that have silicone in them.

For large rheostats I generally use a stiff bristle acid brush or tooth brush with a good cleaner. I also like the products by GC Electronics.

Ron
 
Hi,


I fixed one of my old pots that originally cost about 100 dollars USD, and they wanted something like 60 dollars for repair.
 
"this is a power rheostat, not a low current POT, as I said previously it's power rating is in the neighborhood of 25watts."

I don't understand your point. The spray removes the oxides and leaves a light lubricant.
I have used it successfully on power switches.
and how is that worse than a silicone spray that is non conductive, as others have suggested?
 
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