You can use a cleaner such as Tech Spray's Blue Shower to clean the control. Radio Shack may have contact/control cleaner too (know they did at one time). If this doesn't help you can take the control apart and slightly adjust the the slider contacts so contact will be made on a different area of the carbon element.
Radiodoc
fieldlines.com [great place to drop in on]
The RadioShack spray TV tuner & contact cleaner also works for me, but it seems a little overpriced. It has some mineral oil in it.
RadioShack also has electronics cleaner that comes in a spray can and has a brush on the nozzle; my understanding is that this is pure solvent without lube, so I wouldn't recommend it for noisy pots. It is good for cleaning variable caps, chassis, etc.
:RCA 5T8 1937.
:THE VOLUME CONTROL, IS SCATCHY AND VERY SENSITIVE.IF I TOUCH IT, IT GETS LOUD OR SOFT. SOMEONE TOLD ME, THAT IT'S DIRTY AND TO SPRAY A CLEANER& LUBRICANT ON IT AND THIS WILL CORRECT THE PROBLEM.
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Here's the problem: I used it in my Zenith 5-G-500. Worked wonders. Then I started getting phantom hum/feedback-motorboat-squeel problems after about a half a year. I couldn't figure out the problem. Finally I disassembled the control because it seemed to originate here, though this didn't seem likely at first. Because the WD-40 was simply sprayed into the control, it got all over the metal housing. Then, as time went on, carbon granules from the control element got into the oil film. WD-40 does not conduct electricity by itself, but with carbon granules, it becomes a very high resistance resistor. I even found that there was detectable leakage between the element and its associated terminals and the metal housing--using my multi-meter. I washed out the control thoroughly. This time I put a very thin layer of di-electric grease on the element. I also put some on the shaft since this grease works as well as any other grease, and lasts a long time (doesn't separate like axle grease). Since the grease doesn't migrate, I no longer have the trouble. It's been about four years now, and I have had no trouble.
Recently, after purchasing my DeWald BT-100 television (RCA 630TS chassis) and doing some work on it, I had trouble with the vertical hold control. It was irratic and almost useless. It did whatever it wanted whenever it wanted. This started, of course, after I sprayed WD-40 into the control. It didn't start right away. It started about a day afterward. This circuit, like the volume control circuit of the Zenith portable, is an extremely high impedance circuit, which makes it very sensitive to any leakage. Leakage developed between the element and the housing caused this trouble after carbon granules flowed into the WD-40 film. You see, even though I learned my lesson the first time with the Zenith radio, I just wanted to get this stupid television working in a hurry, so I used the WD-40 trick again anyway. Well, after cleaning the control and doing to it what I did to the Zenith control using di-electric grease, it now functions perfectly always. It's been a year now since I did this, and all is well.
So....a quick fix is WD-40, but it won't necessarily keep things working. Give it a try. If strange things begin to happen in the future, then you know you have to clean your control and use di-electric grease. Di-electric grease really is better anyway. It fights friction much more than WD-40, and lasts longer. Another thing you may want to do with your control is polish the slider contacts. Any sharp flats that have developed on these from wear, can damage the element further, especially if the sliders are at all twisted during any re-alignment. This may expose the sharp edges.
I have two of the most spectacular controls, made by Centralab, here in Milwaukee (don't know if the company still exists... I think it doesn't). In these controls are carbon elements that lie flat against the circumfrence of the housing, instead of flat like a disc. I'm not able to pull the correct words out of my head right now.... Over the carbon element in each control is a band of metal, most likely stainless steel. The shaft is connected to a wiper/slider that has a fibre composit wiper. This wiper faces radially against the metal band so that the metal band is pressed against the carbon element at this point. The metal band is so suspended that it does very little movement across the carbon element as the slider thingie goes over it. In this manner, very little wear is encountered with the carbon element. Kind of neat, hey? I haven't found a use for these controls, though, because they're at like 50 or 100K, which isn't useful for much in high impedance tube amplifiers (perhaps a tone control circuit on the output plate).
Thomas
Would the same concern apply to any contact cleaner that has a lube in it, e.g. a small amount of mineral oil? How about a pure aerosol cleaner without lube?
The problem with the dielectric grease is that you have to disassemble the pot to apply it, correct? I'm all butterfingers, so I try to avoid disassembling pots.
I suppose you can just go ahead and use WD-40, or a similar aerosol, and if it fails, you can then disassemble the pot, which is what you would have had to do originally anyway to apply the dielectric grease?
Regarding your Centralab pot with the deflecting stainless steel disk - I have one of those, and it is a very interesting design. Mine was originally installed as a volume control in an A-C Dayton 3-dial TRF. The shape of the carbon substrate makes it appear that there was an attempt to achieve somewhat of an audio taper.
My Centralab is listed at 200K, but evidently the carbon substrate is gummed up, because it's much higher than 200K, so I had to replace it with a modern pot. I did disassemble the Centralab, which was easy to do, and tried to clean up the carbon substrate, but all I did was make it worse.
Let us not forget that WD40 is extremely flammable too.
Radiodoc
Regarding flammability, well, it is flammable, but I haven't had trouble with it yet. If you spray it into a volume control/power switch, you may see a small flash, but the switch is usually enclosed in such a way that flames can't travel out of the switch. It is usually necessary for there to be about a 1/8 to 3/16 inch minimum hole for a flame to escape, as anything smaller will quench the heat and extinguish the flame. It is probably a good idea to be cautious with it, though. I once used WD-40 on an old snap type wall light switch that was sticking. Well, the switch works fine now, but initially there was a flash out of the switch when I turned off the light. Imagine if the WD-40 had worked its way down out of the box! Also, WD-40 in power switches can do more harm than good. With ignition points in a car it is always a good idea to keep all oils and dirt away from the points, as the soot and flame (small arc flame) from burning oil ruins the contact surface of the points. Switches don't use the special metal that ignition points use, so they're more prone to arcing anyway (momentarily as the contacts are brought together or apart), but adding oil to the area can make more soot and dirt. Still, with that said, I've had more luck with switches that have been oiled with WD-40, than with switches that malfunction and are not attended to. I guess you could start out with contact cleaner and go to WD-40 from there.
Another concern with WD-40 is what happens when you get it on cloth (non-rubber insulated) wire and also on coils (don't spray it on tube sockets, either). With high voltage circuits, the WD-40 can cause arcing between the wires. When sprayed on coils or wires of sensitive circuits, it'll throw off tuning. I sprayed WD-40 on the selector switch of one of my radios, which did nothing bad, but then I sprayed some more and got some on the coils. Well, it took a week before stations went back to their normal positions.
If you have a brightness potentiometer in an oscilloscope like the Heath 0-2, I must warn you to never use WD-40 in this control. With this particular oscilloscope, the anode circuit is connected to the chassis and the cathode is 1,000 volts negative with respect to the chassis. Odd design, but there are reasons for this which I will not get into. Anyway, I sprayed this control in my oscilloscope once, and things really blew up! I wound up replacing the control a couple of times, because it was rather difficult to find a potentiometer that could withstand 1,000 volts. This is also the oddball oscilloscope that uses a 5Y3 as the H-V rectifier. That is, 1,000 volts flows through the 5Y3!
I have to agree with Doug that WD-40 is a valuable tool where radio is concerned. I also have to agree with Radiodoc that caution should be used.
Thomas