ra.ra Posted July 18, 2017 Report Share Posted July 18, 2017 No breaking news here, but I just wanted to share some pics of this half dozen new old stock (NOS) Aetna-Pollak potentiometers that I recently found in a vendor's junk parts bin. This is the first time I've encountered this type with the heavy wiper and spring, and I presume these have never been used since there is no evidence of solder on the wire terminals and no real evidence of abrasion on the moving metal parts. Two items of interest. First, even though these have never been used, some of the metal has still developed some degree of corrosion due to 50 years of varied atmospheric exposure, I presume. Second, I was slightly surprised to see that each pot had a small blob of nearly petrified grease near where the base of the shaft meets the spring - - - its purpose was ........??? And just taking an initial resistance reading between the 1 and 2 tabs (15.0, 14.7, 40.7, 15.2, 15.1, and 14.9), the results were as expected except for this one oddball outlier at 40 ohms. Not quite sure yet how I will attack the clean-and-restore tasks, but I expect I should be able to salvage at least two good pairs from this bunch. Thoughts, questions, comments appreciated. Link to comment Share on other sites More sharing options...
ar_pro Posted July 18, 2017 Report Share Posted July 18, 2017 ra.ra, do the good ones seem to track smoothly across their range? Link to comment Share on other sites More sharing options...
ra.ra Posted July 18, 2017 Author Report Share Posted July 18, 2017 Before disassembly, all of them had good physical movement throughout the entire sweep. Electrically, however, although five of them read close to 15 ohms across 1 - 2 tabs, only three were initially showing a fairly smooth progression from 0.5 or 1.0 ohm minimum up through the maximum. I had been hopeful that all six might perform flawlessly right off the bat, but not so.....yet. Link to comment Share on other sites More sharing options...
JKent Posted July 18, 2017 Report Share Posted July 18, 2017 3 hours ago, ra.ra said: I recently found in a vendor's junk parts bin. "One man's trash is another man's treasure." Nice find, and those are the better ones with the heavy wiper and spring. BUT, they are still corroded and are giving funky readings. I think we have to admit that the A-P pots, along with Callins capacitors and a couple of other vintage parts were just not up to par. Although I'll admit to having used Ohmite pots in my 3a's, there are only L-pads in my future YMMV -Kent Link to comment Share on other sites More sharing options...
genek Posted July 18, 2017 Report Share Posted July 18, 2017 Open-backed Ohmites and L-pads aren't going to be any more resistant to corrosion. Unless you can manage to find some of those super-pricey hermetically sealed explosion-proof Ohmites or there's someone out there producing L-pads with gold contacts. The higher levels of power going through speaker controls (compared to volume controls in preamps) will always promote faster corrosion. There was a reason why AR eventually replaced A-Ps with switches and resistors rather than L-pads. Link to comment Share on other sites More sharing options...
ar_pro Posted July 19, 2017 Report Share Posted July 19, 2017 3 hours ago, ra.ra said: Before disassembly, all of them had good physical movement throughout the entire sweep. Electrically, however, although five of them read close to 15 ohms across 1 - 2 tabs, only three were initially showing a fairly smooth progression from 0.5 or 1.0 ohm minimum up through the maximum. I had been hopeful that all six might perform flawlessly right off the bat, but not so.....yet. It always seems like an uphill fight with these, doesn't it? I really like the idea of an adjustable control, but the switch/resistor method is just so reliable. Link to comment Share on other sites More sharing options...
lARrybody Posted July 19, 2017 Report Share Posted July 19, 2017 Hey ra.ra. Didn't you get some of those 15 watt 15 ohm long shaft rheostats from Bulgaria? Did you ever do anything with them? Mine are still in the shipping envelope. At least you have the better version of the Aetna-Pollak rheostats. I like to treat them with Deoxit Gold after cleaning. Link to comment Share on other sites More sharing options...
lARrybody Posted July 20, 2017 Report Share Posted July 20, 2017 My apologies to ra.ra. It was jkent who posted about the Bulgarian pots. First mistake this week, made it all the way to Tuesday. Link to comment Share on other sites More sharing options...
ra.ra Posted July 20, 2017 Author Report Share Posted July 20, 2017 Yeah, I haven't yet tried those Bulgarian or Russian rheostats yet, but they appear to have a very good build quality and thusfar, performance reviews have been positive. My favorite project using a version of these controls is in this 2ax restoration by xmas 11. http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7994 Meanwhile, I will report back after I dig into these A-P pots a bit more.... On July 18, 2017 at 5:17 PM, genek said: Open-backed Ohmites and L-pads aren't going to be any more resistant to corrosion. I tend to think this is probably true, but I can't recall ever seeing a pic of an Ohmite or L-pad with the typical green oxidized corrosion crust we've all seen with the A-P pots. Since they are all exposed to interior cabinet atmospheres with some humidity present and possibly some off-gassing from stuffing, isn't this corrosive problem largely a result of the specific metals used in these control devices? And with regard to the open-back issue, I'll agree that being covered is probably a preferred installation, but I am not aware of any stated problems resulting from crossovers like these early AR-2 variants. Link to comment Share on other sites More sharing options...
genek Posted July 20, 2017 Report Share Posted July 20, 2017 It's materials plus environment plus operating conditions. The environmental conditions would be humidity, air pollution (both regional and home-specific, i.e., smoking) and outgassing from the materials and chemicals (glue and plywood/particle board binders) in the cabinets. And outgassing would have increased a lot when cabinets went from plywood to particle board. Link to comment Share on other sites More sharing options...
ra.ra Posted July 24, 2017 Author Report Share Posted July 24, 2017 Just a follow-up here. With relative ease, these pots cleaned up very well, and are now probably as good as any A-P pots available these days, I presume. Washed everything in mild soap and water to get rid of residual grease; then a mild soak-and-scrub with salt, vinegar, baking soda and toothbrush on the working parts; then a mild abrasive scrub with soft brass brush; and a spray coating of dielectric silicone. After re-assembly, each one of the six pots provided smooth measurements between a low of 0.5 ohms and a high of 14.9 ohms (have no idea where that earlier 40 ohm reading came from ). These pots came to me with no gaskets, washers or nuts, but the local hardware store had both neoprene and felt washers that fit over the threaded stem, either of which should work to provide a reasonable seal against the cabinet back. I feel fortunate to have found these unused original parts, and this was a relatively simple "restoration", but I have to admit that I don't really enjoy working on these things very much anymore. The sharp bailing wires, the corrosion, the teeny springs, the delicate fit of parts, the multiple nooks and crannies for inspection, the inconsistent measurements - - - sheesh, it's a lot of fussy work for a crucial device that you know may end up disappointing in the long term. Nonetheless, this is a superb sextet, and they will be put to good use. Link to comment Share on other sites More sharing options...
stupidhead Posted July 24, 2017 Report Share Posted July 24, 2017 nice stash Robert Link to comment Share on other sites More sharing options...
lARrybody Posted July 25, 2017 Report Share Posted July 25, 2017 Those look factory fresh. You need two more to have two complete sets. I need a new brass brush for my dremel tool and was wondering if a steel brush would be too hard on these parts. Link to comment Share on other sites More sharing options...
ra.ra Posted July 25, 2017 Author Report Share Posted July 25, 2017 Yes, these pots are like new. About using brushes for cleaning, I certainly think the softer metal (brass) is preferable to steel or stainless steel for this delicate work, and in my case, I didn't even use a powered Dremel - - I simply used a small, hand-held brass brush and a small wad of fine bronze wool. As far as the number of "sets", your count is correct by one estimate (assuming three-way speaker models); however, with my affinity for AR's classic small two-way models, I just might have three sets all ready to go! One pair is already planned for an early pair of AR-6's, but the others have undesignated futures as of now. Link to comment Share on other sites More sharing options...
genek Posted July 25, 2017 Report Share Posted July 25, 2017 I use this after the vinegar-salt soak. http://www.cooltools.us/Scratch-Brush-Pen-Style-Fiberglass-p/brn-207.htm Link to comment Share on other sites More sharing options...
Phxjohn Posted August 6, 2017 Report Share Posted August 6, 2017 Reminds me....I still have 2 pots that I need to send to Larry so that he can rebuild and sell or use in restores. Mine are not corroded at all. They are burned. They came out of a pair of AR 6's that must have been subjected to abuse by a previous owner. I couldn't understand why the spiders were separated from the woofer cones until I saw the burned pots. Link to comment Share on other sites More sharing options...
ra.ra Posted August 6, 2017 Author Report Share Posted August 6, 2017 Phxjohn, those comments are very interesting, but somewhat curious - - not sure I've ever seen a burnt control pot - - - have any pics to share? Being a huge fan of the AR-6, I'm also curious about your woofers with spider separation. I have observed this situation with other speaker products, but never with AR's. Are you sure that the voice coils didn't get fried? ...and genek, I like that scrubby tool, thx for the tip. Link to comment Share on other sites More sharing options...
dxho Posted August 6, 2017 Report Share Posted August 6, 2017 I popped a spider and surround loose on an AR-2 woofer one day. The voice coil seemed fine, though, after regluing with no apparent lingering effects. Link to comment Share on other sites More sharing options...
Phxjohn Posted August 6, 2017 Report Share Posted August 6, 2017 36 minutes ago, ra.ra said: Phxjohn, those comments are very interesting, but somewhat curious - - not sure I've ever seen a burnt control pot - - - have any pics to share? Being a huge fan of the AR-6, I'm also curious about your woofers with spider separation. I have observed this situation with other speaker products, but never with AR's. Are you sure that the voice coils didn't get fried? ...and genek, I like that scrubby tool, thx for the tip. Hi, I don't have any pics to share. The pots are in a box somewhere here. The wipers are the burned parts. I did not know that the spiders were separated until I sent the speakers out to have the caps and pots replaced. The repair guy told me that the spiders were separated. The only thing that I had noticed was that one time when I turned the 6's up, they made some metallic scraping noises. The voice coils seemed fine. But the woofers got reconed as part of the repair. The only original parts of the woofers are the basket and magnets. They sound great. I have the original type 6's with the better woofer and inductors. The bass is sometimes startling. I used to have a pair of 7's. They went nowhere near as low in the bass. For the price...what can you expect ? Link to comment Share on other sites More sharing options...
Phxjohn Posted August 6, 2017 Report Share Posted August 6, 2017 31 minutes ago, dxho said: I popped a spider and surround loose on an AR-2 woofer one day. The voice coil seemed fine, though, after regluing with no apparent lingering effects. I had a pair of 2's decades ago given to me by a friend. I guess one of those had a bad spider as on Luther Vandross' 'Stop to Love' drumbeats in the beginning of the song, there was rattling. This was before Internet days and easy repairs and info. We didn't like the absolute lack of highs. I bought (remember, this is back in the 80's LOL) a pair of metal midrange/tweeter horns from Radio Shack. They came with a capacitor. So I added an L-pad and we were in business. The lows of the 2's and the mids and highs of the metal horns. It actually sounded decent. A new pair of Klipsch KG4's replaced that setup. Link to comment Share on other sites More sharing options...
dxho Posted August 6, 2017 Report Share Posted August 6, 2017 I really didn't like the stock sound either and finally modded this pair with AR-2ax midranges. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.