Replacing Allen Bradley pots

[salomonander]

Hey there,
im working on a minimoog with lots of bad AB pots. Im wondering if it makes sense to replace them with nos allen bradley? Or would they maybe be bad from sitting on the shelf for decades? If so, what would be a good modern replacement?

 

[Brian Roth]

Which model AB pots? The black, 5/8" square "Mod Pots" or the much larger "Type J" with the stainless steel body?

Bri

 

[scott2000]

looks like type J
https://belltonesynthworks.com/2021/03/14/restoring-the-saddest-minimoog-in-the-world/

 

[salomonander]

Yes, they are type j. Most if them are drilled as someone used contact cleaner i assume.

 

[Evertide]

The best way to kill a pot : drill a hole put some contact destroyer in...

 

[Brian Roth]

IIRC Type J pots used a carbon wiper on a carbon track and usually would "clean up" by rocking the control shaft back and forth. But, that only works for so long. Drilled and squirted....all bets are off.

The Mil Spec type for those is RV4. Clarostat used to make conductive plastic RV4 pots as well as a "commercial" version, the 53 series, but I don't know if they are still manufactured.

These folks make RV4 and other styles and Digikey stocks some models.

http://precisionelectronics.com/

Bri

 

[sodderboy]

Try opening two single-stack cans to assess damage. If it is petro-goop on carbon track/wiper there is hope with cleaning and conditioning. If it’s plastic melted by wd40 you have to replace.
I admit, I have drilled as a last resort for sealed clarostats, etc. but the culprit there is usually light wiper tension or stack misalignment on multistacks (sfer).
I’ve thought of an “ultrasonic wand” tool, like a cross between the handimag and the e-bow, that could be used to vibrate a pot in situ. Spray a shot in and somehow zap it with 50k complex wave wand touching the body and exciting the contents. Call it individual “dipping”?
Mike

 

[Brian Roth]

I never had much luck prying open a RV4...but never tried all that hard. Some/many had sort of "shellac" painted around where the steel body attached to the resistive element. I think it was part of the Mil Spec requirements.

I just remembered...Ohmite probably also built RV4 pots. But that is likely another long gone source. The PEC pots from Canada seem to be the last choice anymore.

Bri

 

[Evertide]

Ohmite still makes some...

 

[salomonander]

Thanks guys!

 

[Rusan]

I just remembered...Ohmite probably also built RV4 pots. But that is likely another long gone source. The PEC pots from Canada seem to be the last choice anymore.

Bri

I've used a lot of the Canadian mil-spec carbon comp PEC pots, and they're incredibly well built, feel great and will last forever. But, they do become scratchy pretty soon.

 

[salomonander]

So the PECs are the least desirable? Anyone know the ones by honeywell? They still produce them as well for a decent price.


Doing some research now i found some guys claiming that the PECs only get scratchy if one cuts off the shaft…. due to mechanical strain i assume. Dont know if that makes sense

 

[Rusan]

So the PECs are the least desirable?

I didn't necessarily mean they're not desirable, AAMOF I love 'em.

Doing some research now i found some guys claiming that the PECs only get scratchy if one cuts off the shaft…. due to mechanical strain i assume. Dont know if that makes sense

I've had both some that I shortened and some that weren't go a bit scratchy after less than a year of normal use, while others are still quiet 20 years later. So, I probably should've said, "They can become scratchy pretty soon," instead of "do." I read where Randy Aiken of Aiken Amplification used to use PEC pots exclusively, but stopped after he had some go scratchy in customers' guitar amps. FWIW, the ones I've shortened were done so while holding onto the tip end of the shaft, so there wasn't any stress on the pot itself.

 

[Ike Zimbel]

Yes, they are type j. Most if them are drilled as someone used contact cleaner i assume.

I have some NOS Type J's in stock. What values are you looking for?

 

[JohnRoberts]

Pots do not generally deteriorate from just sitting around unused, ASSuming good environmental conditions.

JR

 

[sodderboy]

And remember, “scratch” is not always the pot but the circuit not at 100% due to other components failing, caps and DC for example.
Mike

 

[JohnRoberts]

And remember, “scratch” is not always the pot but the circuit not at 100% due to other components failing, caps and DC for example.
Mike

Pot noise can be caused by DC or poor wiper contact.

JR

 

[rh001]

Hey there,
im working on a minimoog with lots of bad AB pots. Im wondering if it makes sense to replace them with nos allen bradley? Or would they maybe be bad from sitting on the shelf for decades? If so, what would be a good modern replacement?

Those pots can likely be made like new again using World Pro Audio Brown Stuff followed by a small amount of Clear Stuff. The Brown Stuff cleans and polished while the Clear Stuff protects and lubes. It's more work than the typical mostly useless contact cleaner as you have to exercize the pots (rotate about 20 times) after application of Brown Stuff and then rinse out (with contact cleaner like CRC QD contact cleaner) or chase out with compressed air. Then apply tiny bit of Clear Stuff and rotate 4 or 5 times. Brown Stuff and Clear Stuff have needle applicators so you can put it exactly where you want it. Becuase your pots have driled holes it will be easy to get the Stuff, not so easy to get out. It is not necessary to completely remove the Brown Stuff. A few spurts of air or CRC QD Contact cleaner in the hole will chase out at least half the Stuff...position the spray wand or nozzle so that about half the hole is uncovered to allow escape. No need to flood Contact cleaner into the hole. Test on three pots to get a feel if it's going to work...it usually does. Generous use of paper towel will keep inside of gear clean. https://www.worldproaudio.com/Pro-Audio-Extras/WPA-Brown-Stuff-01

 

[soapfoot]

Related question—

I’ve had decent results rebuilding pots in older equipment when keeping the original pot matters for some reason

These are the scenarios:

1) vintage guitars and amps, where restoring the original pot can keep hundreds or thousands of dollars of resale value, and

2) devices with unusual specs or tapers, where exact replacements are either unavailable or not exact operational replacements (the oddly-tapered Type J in the Maestro Boomerang wah, the odd Italian ICAR pot in vintage vox and crybaby wah pedals, etc)

Usually when I rebuild, I carefully bend the metal tabs out of the way, disassemble, thoroughly clean with 99% isopropanol, add a couple drops of F100L lubricant, and reassemble.

Sometimes this makes the pot like new, but other times it doesn’t fully fix the issue, and I’m starting to suspect poor wiper contact in those latter cases

What would be a rebuild strategy to address poor wiper contact? Gently bending the wiper to try and increase spring pressure?

 

[JohnRoberts]

Related question—

I’ve had decent results rebuilding pots in older equipment when keeping the original pot matters for some reason

These are the scenarios:

1) vintage guitars and amps, where restoring the original pot can keep hundreds or thousands of dollars of resale value, and

2) devices with unusual specs or tapers, where exact replacements are either unavailable or not exact operational replacements (the oddly-tapered Type J in the Maestro Boomerang wah, the odd Italian ICAR pot in vintage vox and crybaby wah pedals, etc)

Usually when I rebuild, I carefully bend the metal tabs out of the way, disassemble, thoroughly clean with 99% isopropanol, add a couple drops of F100L lubricant, and reassemble.

Sometimes this makes the pot like new, but other times it doesn’t fully fix the issue, and I’m starting to suspect poor wiper contact in those latter cases

What would be a rebuild strategy to address poor wiper contact? Gently bending the wiper to try and increase spring pressure?

I recall speaking with some support engineers from Alps decades ago and they were adamant about not juicing potentiometers.

I have never seen worn pot wipers effectively rehabilitated by anything other than cleaning. If the pot element is severely worn, give it a decent burial in the bin.

JR