Bumba Posted February 17, 2020 Report Share Posted February 17, 2020 I had my AR-2 crossover with capacitors as shown in the pictures below. What would it be the correct cap values for replacement? 2uF & 6uF as in the schematic? Quote Link to comment Share on other sites More sharing options...
JKent Posted February 17, 2020 Report Share Posted February 17, 2020 why not keep the originals? Quote Link to comment Share on other sites More sharing options...
Bumba Posted February 18, 2020 Author Report Share Posted February 18, 2020 Hi Kent, Originally, There is no sound through the midrange drivers. But when I hooked them for testing to ar4x, I heard something. Might be the pot? I plan to replace the pots and caps if necessary. Thanks for your help and suggestions. Bumba Quote Link to comment Share on other sites More sharing options...
JKent Posted February 18, 2020 Report Share Posted February 18, 2020 Well, I'm a bit ignorant about the AR-2. I've owned 2a and 2ax but not 2. But here are some thoughts: The original oil caps are probably good and the lack of sound through the mids is probably caused by the pots. If you do replace the caps, you don't need 200V. 100V is more than enough, so you can use Carli, Dayton, Solen or any other film caps. But I don't know about the values. The schematic you posted indicates one 2uF and one 6uF per box. But the first cap (the Astron) is 2x2uF. In other words, two 2uF caps in one can. That Aerovox is a double too I think but I'm not sure about the values. I did some searching and there seem to have been a couple of variations so it would be helpful if you can post pics of your crossovers, not similar ones from the web. And btw that hand-drawn schematic is inaccurate in at least one area (pot is not 10 ohms). Below is the crossover schematic for the Heathkit version. AR-2s may have had the familiar Aetna-Pollock pots while the Heathkit version had pots with metal bodies that look like L-pads. But in both cases it looks like only 2 tabs were used. Hope another member can help here. In the meantime, I would not disconnect anything. Take good photos and draw some pictures so you know exactly how everything is connected. Most people swear those old oil-filled caps are excellent. Maybe you just have really corroded pots and maybe they can be cleaned up. Some unfamiliar territory here for me. btw, once your speakers are up and running it would make sense to re-dope the surrounds (using ONLY RoyC's goo). Kent Quote Link to comment Share on other sites More sharing options...
dxho Posted February 18, 2020 Report Share Posted February 18, 2020 There are 2 x 2uf caps lashed together. Three are connected to make the 6uf, and one is run separately. I replaced the oil caps in my pair; the sound did not noticeably improve. But that would only affect the tweeters, and these don't go that high in the best of circumstances. The pots on these are unique to this model, and apparently do not corrode. At any rate, I'd test the caps and pots before arbitrarily replacing them. This might be one of the few vintage systems that legitimately doesn't need upgrading. Kent is right about the possible use of surround sealer. These are capable of prodigious bass. Quote Link to comment Share on other sites More sharing options...
JKent Posted February 18, 2020 Report Share Posted February 18, 2020 Good info from dxho but I'm still puzzled. If the oil caps don't usually go bad and the pots in this model don't corrode why no sound from the mids? You wrote "when I hooked them for testing to ar4x, I heard something." This is unclear to me. Those mids are actually full-range radio speakers. Henry Kloss used 4 of them in the Baruch-Lang speakers he built in his Cambridge Loft in 1951-52. So the way to test them would be to feed a signal (play music through an amp) directly to each driver (at low volume of course). You should hear more than "something"--you should hear the music clearly. Check all 4 drivers. If any one (or more) is bad, these do show up on ebay. There are some now. See eBay item number: 124038917614 or 174188592580. If the mids are good, then it has to be the caps or the pots. dxho wrote that the pots in these don't corrode, so maybe your original inclination--replacing the caps--was the right thing. If you have a capacitance meter you could check them but most hobbyists don't, and the caps are cheap. Something like this from PE for the 2uF https://www.parts-express.com/dayton-audio-dmpc-20-20uf-250v-polypropylene-capacitor--027-414 and this for the 6uF https://www.parts-express.com/dayton-audio-dmpc-62-62uf-250v-polypropylene-capacitor--027-427 (6.2 is close enough). Or from Madisound, use 2 of these for the 2uF https://www.madisoundspeakerstore.com/m.d.l.-xpp-poly-capacitor-250vdc/mdl-xpp-polypropylene-1.0mfd-250v/ or, if you don't mind soldering a bit to extend the short leads, these 2uF are good https://www.madisoundspeakerstore.com/surplus-capacitors/ and this for the 6uF https://www.madisoundspeakerstore.com/carli-capacitors/carli-mylar-6-mfd/ So. Unless someone has a better idea, first check all 4 midrange drivers and then, if they are all good replace the caps. If that doesn't work we'll have to figure out what to do about the pots but if they are unique to the AR-2 that could be a problem. Quote Link to comment Share on other sites More sharing options...
Bumba Posted February 20, 2020 Author Report Share Posted February 20, 2020 Love the bass so much that’s why I’m trying to make them sing again. Four midrange drivers play music clearly through an amp. I opened the pots and there were small tiny broken pieces of ceramic inner wall scattered inside the spring (forgot to take pics). I will order the caps, Royc’s goo...etc. Can the Ar-2 Aetna-Pollock pots be replaced with Ar-4x pots or with the 8ohm 15w L-pads? Where I can find 15 ohm L-pads? What adhesive can I use to glue the woofer surround to the upper basket metal frame? Quote Link to comment Share on other sites More sharing options...
dxho Posted February 21, 2020 Report Share Posted February 21, 2020 Good to know these pots aren't indestructible. Yours is the first field report of which I'm aware. Quote Link to comment Share on other sites More sharing options...
JKent Posted February 21, 2020 Report Share Posted February 21, 2020 On 2/20/2020 at 5:43 PM, Bumba said: Can the Ar-2 Aetna-Pollock pots be replaced with Ar-4x pots or with the 8ohm 15w L-pads? Where I can find 15 ohm L-pads? What adhesive can I use to glue the woofer surround to the upper basket metal frame? Let's hope someone with knowledge of your pots chimes in. Those were apparently unique to the AR-2. They had only terminal tabs while the AR-4x (and all the other AR model pots) and the L-pads have 3 terminals. I think we have to be patient..... edit: Apparently patience pays off. See Roy's post below. The pots were not unique, just wired differently. Quote Link to comment Share on other sites More sharing options...
genek Posted February 21, 2020 Report Share Posted February 21, 2020 Even if the pots haven't corroded, they can still get gummed up from their environment. 20-40 years in some place where people smoked, for example. I would start by shooting some DeoxiT into the side openings of the pots and working them back and forth to see if anything changes. BTW, from the photo, it looks to me as if the pots do have three terminals. One of them just wasn't used. Quote Link to comment Share on other sites More sharing options...
RoyC Posted February 22, 2020 Report Share Posted February 22, 2020 AR-2 pots are not immune to issues affecting other AR level controls. The primary difference is only 2 of the 3 terminals (#1 and "B") are used, which determine the amount of variable resistance placed in series with the driver(s). The parallel leg of the AR-2 pot is not used, leaving pot terminal #2 unconnected. Terminals #2 and #3 of an 8 ohm L-pad can be used, leaving L-pad terminal #1 unconnected, but the amount of attenuation will be limited to 8 ohms (more than enough for most people) instead of 15 ohms. The oil filled capacitors in the photos above are likely to be OK. I would leave them as is and deal with the pots. Roy Quote Link to comment Share on other sites More sharing options...
Jay Posted November 29, 2020 Report Share Posted November 29, 2020 I've been searching and reading the few forum threads about the AR-2 and its crossover with much interest as I'm finally getting around to restoring a pair of AR-2 which I inherited about 10 years ago. Anyway, it would appear the AR-2 had a "mixed bag" of pots being used during their manufacturing cycle / timeline. The example pictures earlier in this thread show ceramic pots, while the ones in my speakers look like L-Pads, but are definitely pots (see attached pics). After reading as much info as I could find about restoring the early AR speakers I was confused about the pots in my speakers versus example pics and descriptions that others have shared here and AudioKarma. The only reference I could find here describing the pots I have is forum thread AR pots & L-pads AR-2? . That thread was from 2006 and does not include any pictures, but the description of the pot is dead on. Maybe I should put my pictures there as well for reference sake? Jay Quote Link to comment Share on other sites More sharing options...
JKent Posted November 29, 2020 Report Share Posted November 29, 2020 I wouldn't touch a thing. You have oil caps, which are desirable those are not the Aetna Pollack pots. I think they're Clarostat L-pads. Kent Quote Link to comment Share on other sites More sharing options...
Jay Posted November 29, 2020 Report Share Posted November 29, 2020 Hi Kent, Yup, not replacing anything. I measured the resistance across the 2 outside legs, 12.1 ohm. Measured in circuit from center to the open leg 0 to 12.1 ohm smoothly, no jumps or skips. I guess I could properly verify out of circuit, apply a few volts DC on the outside legs and scope the center while I turned the knob, then I could get a visual on the pot condition. But I think it's good to go. Just have to restore the woofer's cloth surround and re-glue the surround back to the basket. Also replace the old broken grille cloth. Quote Link to comment Share on other sites More sharing options...
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