What to clean potentiometers with?

[Leonc]

I haven't done this in a long time...but my power amp (solid state) is developing a scratchy vol pot on one side. I remember from a looooong time ago that there were products (like spray stuff?) for cleaning out potentiometers and other stuff. But I also have a vague recollection of someone telling me that using the stuff was a bad idea. Anyone have any comments one what is appropriate treatment for this condition? (Um, the scratchy pots, not the vague recollection ).

I've been using some stuff called DeOxIt for years to good effect. I believe I got my last can from Lord Valve for about 10 bucks plus postage. Lately I've seen another brand called Rid-Ox from Techspray. Not certain but I believe it is fundamentally the same stuff. It can be purchased online from Mouser. If you don't know about Mouser - www.mouser.com - you need to. They have everything a amp hobbiest could want and they will ship it same day. No order so too small.

[Killcrop]

Radio shack tuner cleaner works well and is easy to get. Just wear safety glasses. The stuff is high presure and sprayed in tight places.

[RacerTippy]

Caig Labs- Deoxit and/or MCL (Moving Contact Lubricant) are the standards.

Caig Labs MCL (Moving Contact Lubricant) is the stuff. Spray through the hole in the case until it starts to drip out. Twist the pot several times. Voila.

Many use Deoxit, but Deoxit will destroy the resistance trace over time. I only use Deoxit on pots that are in really bad shape. I smack them with Deoxit, let them stew, then flush thoroughly with MCL. Twist the pot while the MCL is in there, but avoid doing that with the Doxit to help keep your pot healthy.

Deoxit is great for switch contacts and jacks , however.

And the ProGold formula is the shizzit for tube pins and for sockets.

Just buy the whole set. Available at tech supply houses everywhere, or mailorder from Antique, Lord Valve and many others.

Hasta -> Rico (hanging with Dexter Sinister today...testing my new Sewell Texaplex on Dexter's property. Yow!)

Hey, this is Dexter. Listen to Rico about the Deoxit. Don't ask me why...

DS

[Leonc]

Well, this has turned up more answers than I would have expected.

Check this out:

http://www.midi-classics.com/hardc.htm

Scroll to the Caig products.

If you read about the Caig products being sold here, you get the impression that you want to use DeOxit (of some variety??? but um, which one?) the first time you clean a pot and then MCL afterwards.

Please correct me if I'm wrong.

Here's the deal, if your pot is a bit scratchy and rough feeling, MCL will take care of the problem and improve the performance. If the part has suffered oxidation damage, DeOxit will help reverse that and flush out some of the junk. The problem is that DeOxit is murder on carbon traces. Pots with conductive plastic are fine with it, but standard pots like CTS and Alpha and AB make are at risk of being degraded by DeOxit. The first application doesn't do it, but with repeated exposure to DeOxit the pot gets rougher and rougher and the value shifts and performance deteriorates until its a goner. I ruined an expensive board that way back when I was in radio...Uggh. You really don't want to go there...

MCL will take care of all but the worst problems with pots. If you REALLY need Deoxit, be sure to chase it with MCL to decrease its exposure to the traces.

DS

[Leonc]

Dexter, well...unless I open up the pot and see rust/oxidation, how can I tell if it needs DeOxIt first? All I can tell you is that when I turn it, it feels smooth but is starting to make some loud crackling noises.

I think you should go get a can of DeOxit, a can of MCL and a tube of ProGold. This will fix you up for amp maintenance.

Use the MCL on the pots. Be sure to turn them a bunch after spraying. Then listen to them. If they still crackle, check for DC (what pots are they? Are they isolated by a silver mica cap? Mica breaks down and can leak DC and eventual take the pot out...VERY embarassing during a show!). If there is DC, change the isolation caps. If there is no DC, then try DeOxit and a MCL chaser. If that doesn't work, swap in a new pot.

The Caig products belong in every amp maven's stash.

DS

[ericb]

Originally posted by Dexter Sinister
I think you should go get a can of DeOxit, a can of MCL and a tube of ProGold. This will fix you up for amp maintenance.

Use the MCL on the pots. Be sure to turn them a bunch after spraying. Then listen to them. If they still crackle, check for DC (what pots are they? Are they isolated by a silver mica cap? Mica breaks down and can leak DC and eventual take the pot out...VERY embarassing during a show!). If there is DC, change the isolation caps. If there is no DC, then try DeOxit and a MCL chaser. If that doesn't work, swap in a new pot.

The Caig products belong in every amp maven's stash.

DS

I've used the Caig products since the early 80's.. The Radio Shack stuff is awful... listen to these guys

ERIC

[Leonc]

Originally posted by Dexter Sinister
I think you should go get a can of DeOxit, a can of MCL and a tube of ProGold. This will fix you up for amp maintenance.

Use the MCL on the pots. Be sure to turn them a bunch after spraying. Then listen to them. If they still crackle, check for DC (what pots are they? Are they isolated by a silver mica cap? Mica breaks down and can leak DC and eventual take the pot out...VERY embarassing during a show!). If there is DC, change the isolation caps. If there is no DC, then try DeOxit and a MCL
chaser. If that doesn't work, swap in a new pot.

The Caig products belong in every amp maven's stash.

DS

Goody, once again, I have an opportunity to demonstrate my ignorance.

1. What's DC? Direct Current? Dirty Crud? Daft Cucumbers? Damp Crustaceans? Damn Crackling?

2. How do I tell a sliver mica cap from any other cap? What's an isolation cap and how does it differ from a baseball cap?



Seriously, I barely know a cap from a resistor! The amp is a MosValve 962 stereo power amp and it's one of the vol pots that's starting to crackle.

DC = direct current. The rectified juice that energizes the gain stages (tubes in my case, MOSFETs in yours) is isolated from the amplified AC signal that is passed by blocking or isolation caps. These usually play more than one function and are used both to voice the amp by filtering the signal and stop DC from leaking through. In a Fender style tone stack, the cap that isolates the treble pot from DC is the treble cap, typically a small value ceramic or mica cap. Mica caps sound good and are often subbed for ceramics. Unfortunately, they develop pinholes in the dielectric and leak DC occsionally. This can cause the pot to fail. Prior to that, the DC can be heard in the pot as a scratchiness. Rico taught me a trick: placing a large value plastic DC blocking cap upstream of the tone stack can be a failsafe in case the mica cap goes south but doesn't impart a noticible effect on the voice of the amp.

Anyway, your amp has no tone stack, so there is unlikely to be a mica cap in there. More than likely, the Mosvalve uses plastic board-mounted caps. If I were you, based on what you've said, I wouldn't mess with the board. Spray out the pots and if they remain scratchy, take it to a tech to see if you need the pot replaced or a cap replaced.

DS

[Leonc]

Dexter et al -- thanks for the tips. Finally got some DeOxIt 5% spray and shot a wee bit in there. Boom. Problem gone! Thanks so much for the tips!!

Glad it helped. Its nice when routine maintenance solves a persistent problem. Its the nefarious "rattling cab" phenomena that unhinge me...

DS

[Leonc]

Ah yeah. The rattling cab. I can help you there. My solution has generally been:

1) Drop it from the top floor of a building that is greater than 10 stories high and is surrounded by concrete.

2) Get a new cab.

Sometimes, you have to repeat this procedure a few times to get it fixed right.