owlsplace Posted February 16, 2016 Report Share Posted February 16, 2016 34 minutes ago, stupidhead said: Good morning folks. Sorry 'bout not finishing my post last night but dinner and then some CL transaction activity last night as well, and then this morning I had 2" of snow with a 1/2" of an ice crust on top. Wasn't expecting that and I hadn't positioned vehicles in my normal snow blow configuration. Weird winter so far and I'll be glad when it is over. I seem to be liking winter less and less the older I get! So I see more insights about these various progressions of drivers with AR and links to some great threads with much interesting info. Has anyone actually tried to piece all of this info into some sort of a spread sheet? As for the current project, there are more observations. As my previous post showed, the date on this second woofer is Nov. of '72. More in line with the dates on the mid and high from first. This supports Roy's previous suggestion of the mortited woofer was worked on early on at the factory, possibly a final QC failure as the dates on first woofer are a couple months later? I also see the green splotches on this second woofer, similar to the first. I wonder if this was deliberate or is this just some sort of oxidation and in fact not paint? Keeping with the dating theme, here are some shots of the other driver's dates. I have no idea what the time line from driver production to speaker build was in this era, but all drivers in this one are dated Nov. of '72. These specimens are only 7 apart and I would assume were built at pretty much the same time frame. After digging out all this stuffing, there is nothing different about this board than the first. A little corrosion evident on one of the pots terminals, but no surprises. ... Shirtsleeve weather here My guess is that the drivers were dated at the time of speaker assembly so they could determine warranty coverage. Seeing one pot corroded like this with the adjacent pot not corroded seems to indicate this was a problem with electrolysis. Both pots were in the same environment so the only other variable is the amount of current they were passing. The speaker with the woofer issues probably went in for service as RoyC suggested. I had to return one of my original 5's back in the 70's for a woofer replacement after only having it for a short period of time. Roger Link to comment Share on other sites More sharing options...
RoyC Posted February 16, 2016 Report Share Posted February 16, 2016 Hey Geoff, Same weather here in NY. I stopped liking winter a long time ago. You can measure your caps in place after you remove the pots and rear cabinet terminal jumper, which will eliminate interference from parallel connections and other components. In any case, I would not disturb the solder joint at a cap terminal. Snipping and re-connecting a crossover wire some distance form the cap is easier and safer for the cap. Many AR-5 drivers have a red "5" written on them, but with the exception of the earlier AR-5 woofer I have not found subjective or measurable differences when compared to AR-2ax counterparts. This is a good thing given the relative abundance of AR-2ax drivers available for replacement purposes. Of course there was no fiberglass pad under your other woofer. The ever puzzling but pleasant AR-5. :) Roy Link to comment Share on other sites More sharing options...
stupidhead Posted February 17, 2016 Author Report Share Posted February 17, 2016 OK, so with Roy's guidance I have extracted the pots from this one (29837) and measured all the caps. The results are interesting and please check my math, but it goes like this. 4uf cap measured 8.77 to 9.47 which is approximately 125% out of spec! 24uf cap measured 28.3 firm = 18% out of spec 72uf cap measured 75.5 firm = 5% out of spec I am using a Fluke 115 and am pretty confident in it's performance. I used a new Solen 20uf as a control and it measured 20.2 which is 1% out of spec also note that when the 4uf cap was being measured, it was "floating" around with results while the other three mentioned were stable. My conclusion is certainly the 4 and leaning towards replacing all, what say you? On the pots, I was intrigued by Roger's electrolysis comment, and a picture is worth a thousand words. and of course the one that shows the corrosion is the one with the blue exterior terminal, the other one looks beautiful. I have seen other pairs from same cabs with varying degree of corrosion, but this is a stark difference. Facts like this blow holes in the idea of the "environment" being the force that corrodes these, and seems to speak more to circuitry. Either way, I suspect they will both be usable after a thorough cleaning. I don't know if this is related but when taking off the rear terminal jumper, I detected a loose middle terminal. We have all experienced this and I am always dubious of the wire or connectors ability to make a solid connection on the terminal. Always worried about spinning the inner works, but never seems tight enough. I have a background in water wells, and have experienced a number of times that if a ground wires bond to the copper plumbing is not solid that an electrolysis can and will occur. Is there a correlation? Also note that the inductor wire just off of the terminal screw has a different appearance than the rest of it. Probably from being spun around 360 at least once in it's life, but I am not savvy enough to know for sure. Obviously this will need to be addressed (tightened) before reassembly. Link to comment Share on other sites More sharing options...
owlsplace Posted February 17, 2016 Report Share Posted February 17, 2016 Geoff, If you think you are going to flip them just do the 4MFD cap. I forget what my Spragues measured and I haven't had a chance to A/B them with the other set with the foil caps. I'd have to go back and review the infinite AR-5 thread and then the infinite capacitor thread from last year Electrolysis happens between dissimilar metals and those sneaky electrons always looking for the path of least resistance: the A/P pots use brass rivets and silver plated brass contacts. I don't think a loose terminal on the cab would have any affect but I'm no expert. Also, the cases are left open to dissipate heat and AR just packed them in with fiberglass so might just as well used sealed cases. I gave up on trying to redo those ugly pots. Roger Link to comment Share on other sites More sharing options...
GD70 Posted February 17, 2016 Report Share Posted February 17, 2016 Hi Geoff, You're getting lots of great information on these. What direction are you considering for the pots? Clean and reuse, L-Pads, or Ohmites? Glenn Link to comment Share on other sites More sharing options...
RoyC Posted February 17, 2016 Report Share Posted February 17, 2016 I agree with Roger on all points...and really like his electrolysis theory. I've been into too many AR cabinets with differences in pot corrosion to buy into the high-sulfur-content-in-the-stuffing theory. Stuffing type and/or age seem to have no bearing on the issue at all. In fact, I recently worked on an old pair of Cerwin Vegas with common pink fiberglass stuffing that had crusty green AP pots. (I toss the crusty ones as well, and keep a stash of nice ones for special requests.) ...and I also agree with replacing the 4uf caps and not worrying about the Spragues. Unless equipped with user adjustable measurement settings, most modern handheld meters measure electrolytic caps on the high side due to the very low frequency at which they are measured. Electrolytic caps vary more at frequency extremes than film caps. On the other hand, replacing old electrolytic caps is seldom a bad idea. I would go with whatever provides peace of mind, Geoff. Roy Link to comment Share on other sites More sharing options...
owlsplace Posted February 17, 2016 Report Share Posted February 17, 2016 A pair of defunct AR-5 tweeters popped up locally on the auction site this morning. They must be from the 5's that I missed out on recently. If the price doesn't go too high I'll take a shot at rebuilding these. UPDATE: Someone wanted them more than I did so this project will wait for another day, if ever Roger Link to comment Share on other sites More sharing options...
stupidhead Posted February 17, 2016 Author Report Share Posted February 17, 2016 'mornin' 17 hours ago, owlsplace said: Geoff, If you think you are going to flip them just do the 4MFD cap. I forget what my Spragues measured and I haven't had a chance to A/B them with the other set with the foil caps. I'd have to go back and review the infinite AR-5 thread and then the infinite capacitor thread from last year Electrolysis happens between dissimilar metals and those sneaky electrons always looking for the path of least resistance: the A/P pots use brass rivets and silver plated brass contacts. I don't think a loose terminal on the cab would have any affect but I'm no expert. Also, the cases are left open to dissipate heat and AR just packed them in with fiberglass so might just as well used sealed cases. I gave up on trying to redo those ugly pots. Roger Roger, thanx for the additional insights on all of this. First let me say I am not into the flipping of these or any components I find and choose to rehab. I do understand there is a place and audience for that, but I have a different mentality on all of this. I approach this as a hobby only, and not a business. I have sold some of my projects but I seek out buyers with quality vintage rehab minds. Maybe down the road these stances will change. I tend to be pretty picky in the specimens I buy for rehab, and I don't necessarily consider the value to be a driving concern. This wonderful forum gives me the ability to gain wisdom from from all sorts of like minded people, some who do it for fun and some who do it for gain. On the pots, I will clean and re-assemble and test and likely re-use for this set, or choose some of the stash I have put together which are functional. I do get it that the AP pots are the weak link in the system, but they are OEM and that trumps replacing in my mind. I might be able to crack open the other unit today and inspect pots/measure caps, but right now I am leaning towards leaving the 72's and replacing both 4 and 24. I need some 24's for a JBL L40 set I am working on anyway! Not sure if I will get to the other one today as I am working on the remodel project today, Diane needed to see some progress there as I have been spending a good deal of time in the workshop! Roy, thanx for the insights on cap measuring and duly noted. I very much appreciate the peace of mind comment btw. Glenn, thanx for chiming in as well. I know you are a replacement pot guy, my feeling is that "only if I have to" will I do that. This too may change down the road. Geoff i love this stuff Link to comment Share on other sites More sharing options...
owlsplace Posted February 17, 2016 Report Share Posted February 17, 2016 6 hours ago, stupidhead said: 'mornin' Roger, thanx for the additional insights on all of this. First let me say I am not into the flipping of these or any components I find and choose to rehab. ... Geoff i love this stuff I didn't think you were into flipping. For one thing, the return on time invested is minimal if any. In my own case at this point I need to move out my non-ARs to make room for more ARs Here is a little more input on the Spragues using an Asian-made tester that I picked up to match transistors. It also happens to measure caps and inductors albeit with some limitations. Photos below show a Sprague cap measuring about 7.3MFD on a 6MFD cap used in the AR-7. I presume the Vloss is a measure of dielectric quality and esr represents power loss. I believe this cap would still perform very well as RoyC mentioned this level of tester normally reads high on electrolytics due to their frequency response characteristics. Also, electrolytics that have sat idle for long periods will probably improve as the dielectric reforms with use. By contrast, the Carli 6MFD cap reads 6.1MFD with zero Vloss and an esr of 0.25. I think Klauss previously mentioned the 50v rating on the electrolytic caps offered marginal protection should an older amp fail and dump the rail voltage 80-90 volts on the outputs. The Carli caps are rated at 150V. Fusing is also an option that would protect the woofer voice coil from melt down. (photo sequence got scrambled and the insert function doesn't work as well as the old format so ... ) Roger Link to comment Share on other sites More sharing options...
ra.ra Posted February 18, 2016 Report Share Posted February 18, 2016 Roy, thanks for clarifying the number of iterations of the 10" woofer. I did follow your thoughts on alnico vs. ferrite magnets, but I did not even think about that early wide basket 2ax foam woofer since I've never actually seen one - - was that driver fabricated to fit remaining 2ax cabinets that had already been prepped for the earlier 6-screw cloth woofer? Geoff, we all know you're doing that house addition to accommodate your expanding collection. And Glenn is correct - - you've got a great thread going here. Roger, I'm pleased to finally see someone using one of these small raw digital diagnostic tools, and I'll be interested to see if it creates any discussion. I have never used one myself, but I have been very curious about their accuracy and overall viability. Link to comment Share on other sites More sharing options...
owlsplace Posted February 18, 2016 Report Share Posted February 18, 2016 1 hour ago, ra.ra said: ... Roger, I'm pleased to finally see someone using one of these small raw digital diagnostic tools, and I'll be interested to see if it creates any discussion. I have never used one myself, but I have been very curious about their accuracy and overall viability. Kinda fun item.... I also ordered an o-scope kit that I haven't cobbled together yet I'm sure it is nothing like the old Tektronix dual trace 50MHz scope that I used in the old days ... Roger Link to comment Share on other sites More sharing options...
stupidhead Posted February 18, 2016 Author Report Share Posted February 18, 2016 Neat meter Roger, thanx for sharing. Those tweets will make for an interesting project as well, I will be anxious to see your progress. So, I was able to get into the other cab and kind of more of the same. The pots, while far from perfect are a bit more consistent in their appearance. and to my eye both look reasonably salvageable. I will soak these and polish them up and see where we go. On that note, here is the first set cleaned up. Before assembling I will deoxit all metal surfaces and a slight coating of dielectric grease on contact areas. The pitted one will likely not make muster for the 5s, but have no fear I have a couple spares. Then there are the caps. serial 29844 speaker 72uf cap measured 78.3 = 8.7% out of spec 24uf cap measured 27.5 = 15% out of spec 4uf cap measured 11.5 = 187% out of spec WOW! My course seems pretty straight forward, leaving 72s in place, replacing 4's and 24's. What is that black stuff under the 4uf, seems almost asphalt like. Link to comment Share on other sites More sharing options...
iso Posted February 18, 2016 Report Share Posted February 18, 2016 Roy I opened my AR7 pair as they do sound quite terrible. Air leak around terminal screw might actually be reason for this... but 6 uF axial blue colored Spraque electrolytic of 1974 vintage do measure steady 6,1 with one hand held DVM and 7,4 with other DVM. Are these as high qulity as can style Compulytics... so no reason to worry? Do you kow what was the purpose where Compylytics were used when they were made... I suspect that they were not meant to be used only for loudspeakers? Kimmo Link to comment Share on other sites More sharing options...
owlsplace Posted February 18, 2016 Report Share Posted February 18, 2016 4 hours ago, stupidhead said: and to my eye both look reasonably salvageable. I will soak these and polish them up and see where we go. On that note, here is the first set cleaned up. Before assembling I will deoxit all metal surfaces and a slight coating of dielectric grease on contact areas. The pitted one will likely not make muster for the 5s, but have no fear I have a couple spares.... 4uf cap measured 11.5 = 187% out of spec WOW! My course seems pretty straight forward, leaving 72s in place, replacing 4's and 24's. What is that black stuff under the 4uf, seems almost asphalt like. Did you use the vinegar/salt soak? The black goo is what is left of a piece of foam. Roger Link to comment Share on other sites More sharing options...
stupidhead Posted February 18, 2016 Author Report Share Posted February 18, 2016 1 hour ago, owlsplace said: Did you use the vinegar/salt soak? The black goo is what is left of a piece of foam. Roger Yes on the soak, followed by a triple rinse and a blow dry. I have a dedicated tub just for this. "foam" you say? It has taken on a tar like presence and may pose to be a dickens to get off. Link to comment Share on other sites More sharing options...
GD70 Posted February 18, 2016 Report Share Posted February 18, 2016 Agree with you regarding that pitted pot. I have not done this, but when I was restoring the 3's, someone said they laid down some solder on the disk surface, and filed it smooth, and it worked fine after that. Just a thought. Link to comment Share on other sites More sharing options...
ra.ra Posted February 19, 2016 Report Share Posted February 19, 2016 I suspect this is the early AR-2ax foam woofer Roy mentioned which has the wider basket - note the six screws as opposed to the more typical four. And, not that you really need this, Geoff, but there is a drawing in the Library which actually shows layout dimensions for the screen coverings for the 12", 10" and 8" woofers. Here's the piece that you're missing. Link to comment Share on other sites More sharing options...
RoyC Posted February 19, 2016 Report Share Posted February 19, 2016 On 2/18/2016 at 7:26 AM, iso said: Roy I opened my AR7 pair as they do sound quite terrible. Air leak around terminal screw might actually be reason for this... but 6 uF axial blue colored Spraque electrolytic of 1974 vintage do measure steady 6,1 with one hand held DVM and 7,4 with other DVM. Are these as high qulity as can style Compulytics... so no reason to worry? Do you kow what was the purpose where Compylytics were used when they were made... I suspect that they were not meant to be used only for loudspeakers? Kimmo Kimmo, I've found the large blue 6uf Sprague capacitor to measure well, and not to be the most likely reason for your "terrible" sounding AR-7's. Construction, appearance and manufacturing dates places it in the same family as the other Spragues being discussed here. I seem to recall Tom Tyson mentioning something about AR using military spec caps at one point, but I really don't have any insight into this. Roy Link to comment Share on other sites More sharing options...
iso Posted February 20, 2016 Report Share Posted February 20, 2016 Thank you Roy... I will returnt to AR-7`s when I have proceeded litlle further and got pics. Kimmo Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.