meta_noia_fot Posted March 5 Report Share Posted March 5 Would you replace Sprague capacitors in the AR-10 Pi? I recently did some horsetrading with another hi-fi enthusiast and acquired a pair of -10 Pi's. Overall in good shape. No grills. Tonegen woofers from AR in the late-80's. A dimple on each tweeter but everything functioning. I went into it thinking I'd need to replace the caps. On my first test, there was distortion in the very low end during loud passages. Not much of an acoustic seal so I wasn't surprised. Today I opened them up and this is the first pair of AR's that I've come across that have Sprague caps (for all but the 100mf cap which is silver and in a different typeface). I heard that Sprague caps are often still in spec, so I closed them back up, sealing the woofer using duct putty (anachronistic, but I get a good seal and they carry it at Lowe's). The woofer distortion is gone now after playing back the same material. The midrange and tweeter sound okay to me on initial retesting. I'm sure the caps have drifted somewhat, but if everything is functioning and the drivers "sound" enough alike, would you still replace them seeing as they're almost 50 years old? As for listening, I think these are one of my favorite ARs, behind the -9. The tone controls are interesting on this one. Quote Link to comment Share on other sites More sharing options...
Aadams Posted March 6 Report Share Posted March 6 19 hours ago, meta_noia_fot said: I'm sure the caps have drifted somewhat, but if everything is functioning and the drivers "sound" enough alike, would you still replace them seeing as they're almost 50 years old? About 10 years ago the late @Carlspeak posted a valuable analysis of tests of old bi polar caps he had removed from loudspeakers over years of repair and restoration. He concluded there was no practical reason to remove Sprague Compulytics without outward evidence of malfunction. I have AR classics with all new caps and all old spragues. There is no difference attributable to caps. You have new caps in your AR9s. Put on a favorite recording and compare to the 10pis. They won't sound the same but if they sound equally distortion free you are good to go. I wouldn't change them. Quote Link to comment Share on other sites More sharing options...
DavidR Posted March 6 Report Share Posted March 6 The metal cased canned cap behind the autotransformer might be a Callins cap. They did not use the same liquid electrolyte as Sprague and probably not the same quality winding material. These should be checked/tested. I have MkII 10Pi and all the caps were Callins and needed replacing. Congrats on acquiring a great pair of speakers. Quote Link to comment Share on other sites More sharing options...
meta_noia_fot Posted March 7 Author Report Share Posted March 7 9 hours ago, Aadams said: You have new caps in your AR9s. Put on a favorite recording and compare to the 10pis. They won't sound the same but if they sound equally distortion free you are good to go. I wouldn't change them. So I've now spent a couple of hours critical listening at moderately loud volumes, as well as a couple hours playing music in the background while I play with the kid. I can't hear any clear deficiency. I don't hear any unwanted distortion at all between the -10pi's and the -9's. . I'm going to take your advice and leave the Spragues in place. It's a treat to hear the original caps. Thanks for the heads-up @DavidR. I may open these up again in the next few weeks. I'll take that cap out of circuit and test it if I do. Quote Link to comment Share on other sites More sharing options...
Aadams Posted March 7 Report Share Posted March 7 It On 3/5/2024 at 4:11 PM, meta_noia_fot said: sealing the woofer using duct putty (anachronistic, but I get a good seal and they carry it at Lowe's) I just remembered. In those ADD particle board baffles, the duct seal material can bond to the wood particles. The longer it stays, the tighter the bond. The next time you remove the driver you can pull out chunks of the smooth routed mounting surface. Best bet now days, is gasket tape. Quote Link to comment Share on other sites More sharing options...
meta_noia_fot Posted March 7 Author Report Share Posted March 7 5 hours ago, Aadams said: Best bet now days, is gasket tape. Thanks. I had no idea. I guess between the silver cap and redoing the seal in gasket tape, I’ll be opening these up again soon. Quote Link to comment Share on other sites More sharing options...
meta_noia_fot Posted March 25 Author Report Share Posted March 25 Finished these up tonight. The silver cap was actually an Industrial Condenser Corp. cap. Those two 100 mfd caps measured 148 and 126, so I replaced them. Quote Link to comment Share on other sites More sharing options...
RoyC Posted March 25 Report Share Posted March 25 17 hours ago, meta_noia_fot said: Finished these up tonight. The silver cap was actually an Industrial Condenser Corp. cap. Those two 100 mfd caps measured 148 and 126, so I replaced them. Good call...The large Industrial Condenser caps can be mistaken for Spragues, but seldom measure as well. Quote Link to comment Share on other sites More sharing options...
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