The AM Forum

i bought an aurax exciter rack mount unit at the junk yard yesterday. it works great other than some of the pots are sounding dirty and one of them is non functioning. it uses these particular pots that are kinda thin and have mounting clips to stabilize them on the PCB. they dont have a part number printed on them  so i am having trouble finding replacements.

i'm attaching a couple photos of one. they are 10K pots which i assume are audio taper. the only label is Alpha A10K.

the shaft is 25mm and the body is 7mm thick. the thickness of the body is important because the PCB has electrolytic capaciters directly behind all the pots.

can anyone help me find these things?

Alpha is a low cost Chinese pot that is  decent quality - not great.   A10K means that it is audio taper and 10K in value. B is linear taper

Mouser sell many types of Alpha pots - That's where I would start looking.

Pat
N4LTA

Before you trash them, give 'em a squirt of contact cleaner with silicone in it. 

Work 'em a bit, you may be surprised how they do. :)

73DG

N4LTA, the thing i am having trouble finding is one with the particular mounting clips that these ones have.

W7TFO, i'll give the contact lens cleaner a try. thanks for the tip.

Contact lens cleaner is not what I was referring to.  It may indeed work, dunno. ???

Get a spray can of Caig fader-lube or similar product with lube in it.

You will find it just the thing for noisy pots and plug/jacks.

73DG

ahh thats good to know. however, one of the pots seems to be more then merely noisy. there is no continuity across the pins at all. do you think it could just be grime preventing a connection?

What are you using to check it with?  You need an Ohmeter with a scale up to at least a megohm for a lot of pots.

73DG

i have a fluke 117 which can measure up to 40mOhms, but this pot is only 10K. the other 10K pots measure up just fine but this one doesnt seem to have continuity.

i just ordered some contact cleaner off amazon in the hopes that it will cure the problem.

Here is the USA website and it has a catalog. You can probably call them and find if anyone in the US stocks what you need.

http://www.alphapotentiometers.net/ (http://www.alphapotentiometers.net/)

Pat
N4LTA

the contact cleaner finally arrived in the mail. i sprayed the pot that seems to be broken. it definitely got it moving smoother but there still is no continuity.

i did manage to find a similar pot on the alpha website:
http://www.alphapotentiometers.net/html/16mm_pot_35.html

now i just need to find a store that carriers these pots.


a new problem seems to have come up with the aural exciter. the LED on the 'big bottom' control section is flashing on and off constantly and it is producing a constant clicking noise in the ouput. :(

other than the problematic pots this device was working great when i first took it home. im not sure what happened. all the components look to be in perfect condition.

so i debugged the problem i mentioned in this last post. it turned out that the mounting bracket on the pot that i removed was bridging the ground plane together. when i removed it i split the ground plane. adding a jumper wire fixed all the weird issues.

i also found the pot i need on the alpha website: http://www.alphapotentiometers.net/html/16mm_pot_35.html

however i havent been able to find it for sale anywhere. i called alpha and they said they have minimum orders in the thousands.

any ideas where to get this pot? i need the one with shaft A, taper A, and 10kohm.

Submit the complete Alpha part number to Mouser and Digi-key and see if they can ordered it from Alpha.
Actually, there is an Alpha A10K (audio) pot on ebay eight now for sale: http://www.ebay.com/itm/Alpha-Potentiometer-Pot-16mm-A10K-Audio-Taper-/310094795183 but probably not usable unless modified and a bracket fabricated for it. You would probably have to relocate, or modify position, of any closely mounted components.

All the Alpha pots I have here say Taiwan.

pete. that pot is not gonna work. in addition to the mounting bracket (which is only important because it bridges the ground plane) the pot needs to be extra thin. the pcb has two electrolytic caps directely behind the pot which prevent me from using a standard size pot.

ACK!!!

This term "contact cleaner" is being bantered around here and its frightening me.

First off, never never use "contact cleaner" of any kind on a pot. It's a resistor not a metal contact. Normal contact cleaner is designed to remove oxidation from metal. On a pot, especially a carbon comp, it will remove the carbon coating as if it is oxidation. This is what leads to premature failure of pots 90% of the time. People unknowing spray all sorts of things into pots to remove dust, dirt and oil not realizing if they are using an incorrect fluid they are also removing or softening the resistive surface. I hate the term "contact cleaner" being used in discussions threads about cleaning dirty pots.

Caig Fader-lube is about the only product that is out there that does its job and doesn't damage the pot in the process. They're product called De-Oxit should NEVER be used in pots. WD-40 is right out!!! Also any electronic degreasers are bad as well. High purity alcohol is better in a pinch, but questionable also, depending on the pot type (some use plastic substrates that do not like isopropyl alcohol, especially some Chinese made pots.)

It is highly likely all the problems in those pots in that Aphex unit (I'm assuming that's what you have there) are probably the result of some witless studio tech or DJ spraying "cleaners" into dirty pots at some point, solving the problem in the short term but effectively giving the unit terminal cancer in the long term.

If you give me the correct make, model & serial number I may be able to source the part for you. The bracket is not only important for grounding, it also is the only mechanical support other then the leads themselves (I always hated this PC mount pot type used to save thousands by companies who wanted to get away from buying hardware for panel mounting. Cheap shit design methods.)   

Now I know we are gonna hear from the "I've been using this or that for years with no problems" group. Well my response to you is; no problems? ... yeah ... not yet.

John

ackkk is right! when this can of dexoit cam ein the mail i went crazy with it and sprayed all my audio gear with it! can i mitigate potential damage by applying fadelube after deoxit?

john, the part number for the broken pot is: 3RP/1614N-C-A1-A 10K

it would be awesome if you could help me source it.

I noticed that some hams feel very strongly against certain types of cleaning fluid. Its really quite comical. Dare I say that these hams are Smug over the proper us of such miracle fluids??  :P

Almost all of the ranting is 100% complete total BS. Its probably once a week I hear some old codger (Noun 1. old codger - used affectionately to refer to an eccentric but amusing old man) going on and on about how bad this is and how good that is.  They go on to say if you spray that or use this your DOOMED.   

As for De-0xit.  I have used it for more then 15 years.  There are other types of de-oxit.  My brother buys and sells audio gear and has sprayed different types of caig into thousands of dirty potentiometers, switches and sliders.  Never once has a failure and more then 90% of the time, The scratchyness is gone. With D5, You spray it on. Let it sit for an hour so it can do its job and then work the switch a bit.  You DO NOT hose it down, and turn the gear back on that instant and you DO NOT spray it in with the gear running.  You let it sit and you scrub the contact with a brush if possible. It has naptha in it and will light up in flame if you turn the gear back on before the naptha evaporates.

Many hams swear by chevron "techron" which is available very cheap at any autoparts store or even wally world.  There was an article about using this on pots an switches in ER a few years back.   Hams like the techron because you can get a big bottle for a few bucks.  Caig chemicals are expensive

C

OK ... like I said. The I've been doing it this way, non-scientific guessers have arrived.

Excuse my "rant" that follows if you have no interest in science and facts.

The fundamental science here is chemistry. Not some "miracle" from divine intervention. Most of the spray type "cleaners" use carriers and propellants. Most times the propellants are either propane, isobutane or pentafluoropropane. The carrier in most electronic washes is usually isopropyl alcohol. Sometimes acetone or other petroleum distillates are used as carriers in industrial electrical & mechanical washes such as the case of WD-40, as well as common "degreasers" used for electric motor cleaning.


You can see in the above image the carbon based resistive surface printed onto the substrate. It is a very thin coating in most pots and prone to wear and also dirt lifting the wiper. You can see the three groves left in the carbon by the three tip wiper, used for redundancy to mitigate this lifting issue. The groves and the build up of worn off carbon is clearly shown in this well used pot. This pot was obviously cleaned and the lubrication is missing and probably as a result leading to this wear. The straight scratches are probably a result of the dis-assembly of the pot for this image. However, you can see at the 8 o'clock position wear at the most commonly used setting for this pot. The pot shows the classic signs of no lubrication over time. Some pots use a plastic substrate and resistive surface which is more reliable but also prone to the same problems in regards to this discussion.

Isobutane and particularly pentafluoropropane have properties that cause the carbon composition applied to the substrate to either soften or lift away. Isopropyl does not affect the resistive surface as badly. Petroleum distillates such as acetone and others, are the worst in this respect. The propellant used in Caig Fader-lube spray is diflouroethane, which has the ability to deliver the lubricant, and not chemically degrade the molecular bond between the resistive surface and substrate. The sprays that "leave no residue" remove lubrication that is inside the pots which is there to prevent mechanical frictional wear between the carbon or plastic conductive surface and the metal wiper.

FaderLube lubricant is not silicone, but instead is a conductive lubricant in the Teflon family. Silicon lubricant actually will act as an insulator between the wiper and the conductive surface. The exception to this are the silicone greases which have silver or some other conductive material colloidally suspended. However most, and I say most, of the conductive silicon types are not used since they actually conduct, which in this case would render the pot shorted. These are the types you see used for antenna joints and grounding fittings. Point contact conduction type lubricants are what are used in pots.

Of the silicon lubricants, the worst to use is WD-40. It contains the worst chemicals for this application. All the propellants are of the worst kind, the carrier is a petroleum distillate and the lubricant is a non-conductive silicon. The carriers also have a tendency to dry and harden over time leaving a gunky film inside the pot. This gunk also has the nasty tendency to attract dirt and hold it in place, which will scratch the resistive surface. Now if you want to remove a stuck bolt in your car, liberally use WD-40. Spray away! But use this goop where it is appropriate.

Incidentially, trichloroethylene the so-called wonder solvent isn't even good to use on pots. Barring the obvious health risks (ALS, anesthetic reactions, possible cancer risks) This very effective degreaser also strips away all the lubrication inside the pot leaving it prone to excessive wear. NASA began a test program exploring this very question since trichloroethylene was in use in the United States to clean kerosene-fueled rocket engines. Early on they noticed problems with certain associated mechanical electronic components exposed to TCE, particularly premature failure of potentiometers, servos & encoders. The cause was attributed to removal of lubrication.

So, what about Techron? Techron is polyetheramine. Basically a detergent, but not quite in the traditional sense. What it is designed to do is lift, release and capture carbon deposits, produced by the presence of hydocarbons (fuel or the by-products of its oxidation), from inside an internal combustion chamber by either being mixed with fuel or the lubricating oil. To put it simply, it is a compound that has an oxygen ion present that causes the carbon (and other related compounds) to bond to it and be removed via the exhaust. The idea is the carbon compounds bond to the Techron before it has a chance to bond to the metal surfaces of the engine. While Techron looks just like De-Oxit and is much cheaper, it is a completely different compound intended for a completely different purpose. What possible advantage is there in using an estermine in a pot? Furthermore ask yourself, why would you be using something that is intended to bond and/or capture carbon compounds?

Now bear in mind, most times the softening of the resistive surface is such that it simply causes premature wear from friction. This causes the life expectancy to drop on the pot. Basically, it will wear out much faster. The combination of this additional wear and the removal of the lubricant exacerbates the issue. Which is why using just alcohol is not preferred since even though it doesn't soften the carbon as much, it does remove the lubricant.

Now the actual lubricant used by Caig in FaderLube is a "trade secret" but most likely it is some lubricant that falls under the MIL-PRF-46002 mil spec. However, the specifics of the lubricant is not what is the issue here. It is the carriers and propellants that cause this damage to pots. The effects of which are slow, but real. The denials of guys who have used these other products with no problems not withstanding.

If one took the time to look you would find that Caig themselves warn that regular De-Oxit is not recommended for carbon comp or plastic potentiometers, and refers people to use FaderLube.

While you used De-Oxit on your pots, this is better than using other things like degreasers or WD-40. It would be a good Idea to pick up a bottle of 100% Faderlube, which has no carriers. This will keep the pot lubricated and smooth and will mitigate any softening that may have occurred from the pentafluoropropane used in the De-Oxit spray. One way to tell the difference is FaberLube is green, De-Oxit is red. Below is a picture of a bottle of the pure FaderLube, a bottle of which will last years since you only need a drop or two for each pot. It comes with a needle tip applicator.



Now, there also are many other products made by other manufacturers that fall under the MIL-PRF-46002 specification and work exactly like FaderLube, but the Caig product is mentioned here since it is widely distributed and readily available.

I will tell you little story about folks who say "I've used it for years". I once was hanging with a guy who was working on a piece of audio equipment. He told me about how he uses gun products to clean electronics. He started spraying a chemical used to clean gun barrels. After he sprayed this stuff, I noticed black stuff running out of the pots. I said he better check those pots since I think the carbon just got removed from the inside. After the thing dried, it was not working at all. This product, which he claimed he used all the time on electronics, is normally used to remove carbonization that occurs inside gun barrels. Well it did a good job of removing carbon, that's for sure. In his defense, he was working on an older piece of gear which had carbon pots, not the plastic types in the more modern gear he was used to. So pay attention to the science & facts, and be skeptical of unsubstantiated opinion.

Anyhow, I need the make, model and serial number of the piece of electronics, not the part number for the pot. I should be able to source this out for you this way.

John, W2WDX

wow! john that is an incredibly detailed response. i never expected to learn so much about potentiometer construction and maintenance.

as far as the device in question, it is the Aphex 104 Aural Exciter Type C2 With Big Bottom. On the back it has the code AX104-3351 printed on it. the manufacturing date is 10-96.

the particular pot in question is a 10k audio taper pot for the mix control on one of the aural exciter channels.

Why not call Aphex and get a new pot?  They stock them and are cheap.

John. Thanks for the post. You have an incredible amount of time on your hands I and I envy that!  Off to work I go.


C

I just have way to much information stuffed in my cranium, and I can type really, really fast.

J

i actually did call them and they seemed pretty open to looking for parts. they asked for details on what i needed and my contact info but i never heard back from the. that was a couple weeks ago.

I thought WD40 was liquid pig fat