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Thread: Take a look at this Impedance selector switch. Not sure what to make of these terminals?

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    Take a look at this Impedance selector switch. Not sure what to make of these terminals?

    Not sure if I've ever seen one in this condition?? This is labeled as NKK, which makes high quality switches, but I've never seen any of their switch terminals suffer this kind of blueing before. I'm wondering if this might not be a counterfeit production.



    What do you guys make of this?

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    It looks like silver sulphide, which initially forms a yellow and blue rainbow-type discoloration and then eventually turns black. Note that the areas around the solder joins are protected with flux residue. It often forms as a result of atmospheric contamination.

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    I've seen similar things happen when I accidentally leave my iron on too high. Doesn't happen on everything, but sometimes... Especially with those block-shaped red plastic speaker jacks with wide terminals & other things with tabs like that.

    Justin

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    If you have some household ammonia you can dilute it a little and use a q-tip to see if it removes the discolouration. If it does I'll bet the contacts are silver plated.

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    Supporting Member SoulFetish's Avatar
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    Quote Originally Posted by Mick Bailey View Post
    If you have some household ammonia you can dilute it a little and use a q-tip to see if it removes the discolouration. If it does I'll bet the contacts are silver plated.
    I just checked the datasheet for the HS series switches and they do have some models with silver plating.
    I've just been reading up on silver sulphide, silver plated contacts, and problems leading to contact failure. Pretty interesting paper here, and a quick read:
    2002 technical paper - Silver Corrosion

    If this is corrosion of the silver plating on this switch, It makes me question the wisdom of using untreated silver plating on exposed/open switch contacts.
    I used to work for a jewelry manufacturer, and they would use Rhodium Plating to maintain the silver finish and prevent tarnishing.

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    Old Timer Leo_Gnardo's Avatar
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    The wiping action as you work the switch scrapes off the soft corrosion layer, as you can see in the photo. And if you're worried, apply a tiny dab of DeOxit to the terminals. Those switches if I'm not mistaken are rated for some enormous current, something like 30 amps. The most they'll see in any tube application might be around 1/3 of that, in a 300W amp running a 2 ohm load, half that for most any more common amp/load combination

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    Bent Member Chuck H's Avatar
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    This^^^^^^^^^^^^^^^^

    A little reading on line indicates that silver plated contacts aren't ideal for low voltage applications. And this would be a low voltage application. I think, clean them and apply one of the tacky/viscous type contact treatments. I don't even know who makes stuff like that, but I've seen it on many switches I've serviced. The DeOxit product Leo mentioned may be one of them. I've never bought the stuff.

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    Quote Originally Posted by Chuck H View Post
    The DeOxit product Leo mentioned may be one of them. I've never bought the stuff.
    DeOxit is typically supplied as a 5% spray, the remainder being mostly naptha which is a darn good cleaning solvent. IF the DeOxit formula is still the same as Cramolin, its predecessor (available since 1928 !) , the old advice was "the less you use the better it works." So having a glob of DeOxit or Cramolin on the contact works against you, can bring on more corrosion & make for a lousy contact. When the stuff was gaining popularity in the hi fi world, late 1970's, some people overdid it, gooping up their tube contacts & everything else in sight. More is better, right? Not in this case. Just a couple of molecules is plenty enough apparently. Apply a dab with a Q-Tip, toothpick or something like that, give it a few minutes to do its thing, wipe off the remainder, maybe with some solvent. What little remains is enough to maintain a good contact.

    FWIW Caig has a paste formula intended for high current applications. I let my brother know this - he works for Teledyne Continental - manufacturer of piston airplane engines. I think they now use the stuff in their magnetos. And Caig boasts lots of other hi tech manufacturers & organizations in their list of satisfied customers. Like NASA and Boeing. (No, DeOxit didn't figure into the demise of those dodgy 737's.)

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    Bent Member Chuck H's Avatar
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    So what IS that transparent amber, tacky stuff that I find on old switches and sometimes even jacks or pots? Which, BTW, are rarely oxidized where that stuff is still present.

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    Quote Originally Posted by Chuck H View Post
    So what IS that transparent amber, tacky stuff that I find on old switches and sometimes even jacks or pots? Which, BTW, are rarely oxidized where that stuff is still present.
    Yes I've seen that too. I suspect it's just regular old grease that's oxidized with age. I find it in various bits of cars I've worked on too, most have nothing electrical about them. In old turntables too.

    Heck I just washed up an old Revere ware pan that's hanging on my kitchen wall, haven't used it since Esther was a pup. Plenty of sticky grease & bits of fiber stuck to that ol' relic, just from exposure to the typical kitchen atmosphere contaminants. Crap, I'm gonna have to get a new dish scour/sponge now, that mess gummed the old one up badly. No matter, it's about time anyway.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Leo_Gnardo View Post
    Yes I've seen that too. I suspect it's just regular old grease that's oxidized with age. I find it in various bits of cars I've worked on too, most have nothing electrical about them. In old turntables too.

    Heck I just washed up an old Revere ware pan that's hanging on my kitchen wall, haven't used it since Esther was a pup. Plenty of sticky grease & bits of fiber stuck to that ol' relic, just from exposure to the typical kitchen atmosphere contaminants. Crap, I'm gonna have to get a new dish scour/sponge now, that mess gummed the old one up badly. No matter, it's about time anyway.
    Ok. I can buy that, but the stuff I'm speaking of seemed to me more often exclusive to contacts, evenly distributed (never globy) and always has the same smell and color.?. Also, I know that grease and anything viscous can gather dust and crap that can foul switches, but this stuff never looks dirty. Maybe it's just old grease, but if so they should come up with a way to make something like it for application on contacts

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    There is certainly something like contact grease. E.g.: https://www.amazon.com/LubriMatic-11.../dp/B001446LP4

    The grease found inside pots is typically for lubrication and friction control of the shaft. It is not meant to be on the carbon track.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Helmholtz View Post
    There is certainly something like contact grease. E.g.: https://www.amazon.com/LubriMatic-11.../dp/B001446LP4
    I know THAT stuff. Could work I think. My consideration is that those contacts could be cleaned and then something applied that will stay put to keep them from further oxidation.

    BTW, don't get any of that stuff on your hands or you won't be able to pick up or hold on to anything for a day or two!

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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    BTW, don't get any of that stuff on your hands or you won't be able to pick up or hold on to anything for a day or two!
    Means that it probably contains silicone grease, which doesn't easily wash off with soap.

    Often Vaseline (petroleum jelly) is used on contacts. But there are more specialized products sold e.g. by ElectroLube.

    But any contact lubrication on moving contacts will reduce the self-cleaning effect described by Leo, so I'm not sure if it's always a good idea.

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    Last edited by Helmholtz; 02-15-2020 at 08:06 PM.
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    I don't like silicone grease near contacts. It migrates, causes problems with resoldering and can prevent non-wiping contacts (such as found in rocker switches) from making contact. I prefer RS components contact grease for some contact types, but only where necessary. Kontakt Chemie 60 is really good for removing silver sulphide and leaves a protective film.

    The grease in pots is sold under the brand Rocol Kilopoise. As a good substitute use PJ1 chain lube - spray it into a small container and let the solvent evaporate. I use this a lot when rebuilding pots and want something a little more gap filling than kilopoise.

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    Looking at the picture, I don't think there is a problem with the switch at all. The contact area looks shiny and like others said, all it might need is a little Kontakt 60 (followed by Kontakt 61) or Deoxit applied with a Q-Tip and a few turns to wipe the contacts.

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    Don't forget the joker g1's Avatar
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    Somebody gave me a can of this stuff, it's lanolin based and gets very viscous. Maybe similar to what is being described.
    https://www.fluid-film.com/

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    Quote Originally Posted by g1 View Post
    Somebody gave me a can of this stuff, it's lanolin based and gets very viscous. Maybe similar to what is being described.
    https://www.fluid-film.com/
    Lanolin is wool wax and I don't think you want it on high current contacts.

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    I use something similar called Tectyl to prevent winter salt corrosion on cars and bikes, and some other outdoor stuff prone to rain exposure or workshop equipment subject to condensation.

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    I agree with Helm, the contacts look OK. I consider them self cleaning. All that tarnishing where the contacts don't rub? Who cares, they are not contact surfaces touching.

    I worked in the coin-op amusements industry a long while, and back in the old days, when pinball machines were full of a ton of relays and stepper units with brass feeler contacts, we might put a thin film of light grease on the wiper discs to reduce wear, but otherwise they tended to keep themselves clean by rubbing. In fact in relays, there is something called "scrub". As contacts just close, they touch at some point on their surfaces. As the contacts continue to close tighter, the individual contact points slide slightly across one another. That is called scrub, and tends to self-clean the contacts. I did have to burnish relay contacts now and then, but it was from arc pitting, not dirt.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Enzo View Post
    I agree with Helm, the contacts look OK. I consider them self cleaning. All that tarnishing where the contacts don't rub? Who cares, they are not contact surfaces touching.
    I'm cool with that, with one caveat. It's an impedance switch. There's a good chance under many circumstances that it could be left in one position for a very, very long time and the unused contacts could develop their maximum oxide thickness. Maybe it'll scrub right off by switching? Some reports say it can be a problem. In this particular case, being an impedance switch, that would leave the output unloaded (= bad). I did read that this oxide layer tends to be less of a problem in higher voltage circuits.?. But an impedance switch in a low voltage circuit.

    I'm just saying that a cleaning and a little electrical grease on the contacts to keep them from oxygen is probably a lesser evil than whatever debris might collect on the grease.

    JM2C

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    Supporting Member SoulFetish's Avatar
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    Quote Originally Posted by Helmholtz View Post
    Looking at the picture, I don't think there is a problem with the switch at all. The contact area looks shiny and like others said, all it might need is a little Kontakt 60 (followed by Kontakt 61) or Deoxit applied with a Q-Tip and a few turns to wipe the contacts.
    The contact area in the middle terminal (8Ω selection) is the switch position that was and is normally in. It was not cleaned by the switching action, nor did deoxit remove the discoloration. I don't think that the switch contact to the right looks very good at all.

    I would have to agree with Chuck on his point. If this was a switching jack in the signal chain, or a relay, I could chalk it up to a nuisance probably. But the fact that the full output goes through this switch, the condition increases contact resistance, which increases heat–which worsens the tarnish–compounding the contact heating, etc. This could lead to a switch failure and potentially cause costly damage to the amplifier.

    My point here is that silver plated open air contacts, supplied or left untreated seems lazy or negligent on behalf of the Manufacturer. It does not take long for silver to tarnish, and the technical paper I posted above articulates the the mode of failure, and provides some good examples of preventative measures.
    In situations where untreated silver plating is used In critical locations, it's my opinion that taking some of these simple measures is the wise choice.

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    Last edited by SoulFetish; 02-16-2020 at 09:11 AM.
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    From the paper:

    "Sealing out corrosive gases can help to protect metal surfaces against atmosphericcorrosion. Corrosion inhibitors/lubricants applied at any sliding contact points andsurfaces will do this job very well. Special attention should be given to the correct choiceof these products to not induce interference with electrical properties of conductive parts.Effective lubricant for electrical parts should be chemically inert towards the metalsurfaces to be lubricated. Lubricants used on silver-plated surfaces should not carrysulfur-containing compounds. Lubricants for electrical parts should not collect dust and particulate matter, should beresistant to oxidation and chemically inert to corrosive atmospheric components. Theselubricants should not build non-conductive deposits on contact surfaces after multipleoperations and retain long-term thermal stability at least up to 400 oF. Any corrosioninhibitor must be thoroughly tested for electrical application."

    Not everything that works for car battery poles (extreme contact pressure) is suitable in electronics. I am not sure if (non-conductive and sticky) grease is suitable for every high current switch.

    I doubt that the performance of the switch shown could be improved by any contact grease. OTOH Kontakt 61 applied after cleaning with Kontakt 60 or Deoxit will leave a non-sticky protective film.

    In case of doubt I would ask a major switch manufacturer.

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    Last edited by Helmholtz; 02-16-2020 at 08:17 PM.
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