Potentiometer Rebuilding (Not for the faint of heart)

[Jacampb2]

No, you explained fine, I just wanted to point out that even in PG's amps they sometimes use a linear gain control. I realize you were reusing the old elements, I just thought it might cause confusion to someone else when they look up a 10K part number and discover their amp is 50K-- I know this isn't the point of your "how to" here, but I can see it causing someone confusion-- I know it made me double check my notes, lol.

Anyhow, it looks really good. Panasonic also has a pot that is almost the exact same design as this one, it might be worth digging through their catalogs. I am not sure if they have a dual gang snap in, but they might. Might give you another option for cannibalizing. For the most part, the best I can find off the shelf anywhere is dual gang units. I don't even know how you would go about finding some of the multi-gang pots in the multi-channel amps.

Oddly, the Alps pot you found there I cannot find listed in my current mouser catalog. I did happen to find that they make some with a metal shaft, dual gang, in a few different tapers and 10k, 50k, and 100k. They aren't snap in though, but I think they were still 9mm. They actually looked a lot like the Ti pots, I couldn't pull the data sheet for them though, the link was wrong and kept getting me Alps rotary encoders and I didn't pursue it further.

Ok, I'll quit rambling in your thread, good work! I'll run outside right now and look for that grease.

Later,
Jason

[oldschoolfan]

I am confident they can be cleaned, but my concern is finding a good grease to use once they are clean. The contacts need something to protect them from oxidation, however, it cannot be conductive (conductive would defeat the whole use of the pot).

Couldn't you use dielectric grease?

There are lots to choose from. Which would you suggest? I think clear would be better than the white stuff. Last thing I needs is white goo leaking from a pot on an amp.

I am no grease expert. I always use the stuff from the auto parts store made by Permatex. It comes in a metal roll up tube, and it is clear. I use this stuff for any and all electrical connections on a vehicle that may get exposed to the elements. Had great luck with it for that type of use.

[Eric D]

I think these pots just showed up at Mouser, so that might be why they are not in the catalog. I know I never seen them at Mouser's site unit just this week. And over the years I have spent many times trying to find these parts.

I took my method a bit farther today.

First a guy I work with laser cut me some small blocks the same width as the pots. I had him cut a few sizes (they should be 0.390in), to take into account any deviation from the laser. I then dug some brass strip out of the parts box. This stuff can be found at any hobby shop for a few bucks, and will be enough to do MANY pots...



I used the right sized block to bend the brass into a form similar to a staple...



Then it became a matter of putting it in place and soldering it in...





Lastly I used needle nose pliers to put pressure on the clips and then reheated the solder so the pot was held together tightly. Part of the problem with these amps over time is the pots tend to wear and become loose. Plus those small plastic rivets become loose over time as well. Instead of just automatically removing and replacing the pots (assuming I even have any spares at the time), I am going to first put a clip on them to see if they improve at all.

[stipud]

Lastly I used needle nose pliers to put pressure on the clips and then reheated the solder so the pot was held together tightly. Part of the problem with these amps over time is the pots tend to wear and become loose. Plus those small plastic rivets become loose over time as well. Instead of just automatically removing and replacing the pots (assuming I even have any spares at the time), I am going to first put a clip on them to see if they improve at all.

Not a bad idea. The oxidization may not be the problem so much as the clamping force of the case...

[Eric D]

I am sure the oxidation is the main problem. It is very hard to show with photos, but the wiper assembly in the pot has its own spring force. All the knob does is turn the wiper assembly. On the knob itself are small "wings" which rub against the metal outer housing to cause resistance to motion. When the plastic rivets become loose, the metal moves away and the knob begins to "flop around" a bit. At this point there is nothing really holding the knob and therefor the wiper assembly in one place.

But, I do suppose if the pot was bad enough the two gray plastic housing halves started to separate, then there would no longer be enough spring force in the wiper assembly to maintain contact. My guess is both the soldering on the board, and the small tab on top will keep the two halves of the housing together though.

[Jacampb2]

Eric, the dielectric grease I have is simply called Dow Corning 4, it has a dielectric strength of 450 volts per millimeter. They make others, however, not many of them are "clear" transparent. This is. It isn't cheap, McMaster Carr sells it for $15 a tube.

Later,
Jason

[holmis]

Is this the same ? Valek1 sells them on ebay

http://cgi.ebay.com/NEW-ALPS-Dual-Pot-1 ... 43a1da0060

[Eric D]

Valek1 sold me some 10k pots before and they were just fine. I then bought some 50k pots from him, and they became the reason for this thread I started. They were the wrong ones. He did not realize it either when he sold them too me.

I don't know if he is getting old stock OEM ones, or ones from Mouser. I also know his crossover control pots are the real deal. I got some of them and they were 100% compatible.