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About johnieo

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  1. johnieo

    AR-6 with zobel

    IRa.ra: At this point, Iwould replace the capacitors. No elecrolytic made in those days was intended to last this long! The Sprague and Compulytics made in the 1970s were well made with low ESR. If one looks in the old Handbook of Components for Electronics or the Electronic Engineer’s Master (EEM) available in your friendly nearby University library, one will see ESR values of order 0.016. The demand for switching high currents in capacitors while minimizing heat generation was the driving force behind these quality capacitors. Bridge measurements that I made in 2005-6 showed the capacitance values to be close to original value, but the ESR to have increased considerably. To evaluate these capacitors one needs a bridge that will measure both C and ESR in the octave or so frequency range near the crossover frequency of interest. Cant be done with large capacitors on a small L/C/ESR meter. Cheers and enjoy refurbishing these--its a fun hobby. John
  2. johnieo

    AR Restoration Meeting--1

    The correct numbering of the International Division meetings may be obscured in the dust of crumbling surrounds. I do recall meeting at Organ Stop Pizza, Mesa, AZ in 2009 with Richard Lowe (Melbourne) and Ken Kantor. That meeting followed one between Richard and Klaus in Denmark (2008??). Perhaps there were several others? As a physicist, I would accurately call the most recent Rome meeting number "N + 1" Finally to complete Kent's meeting definition---photo and sustenance---we might consider including a pint or a maß (for those so inclined) hoisted in toast to Edgar Villchur ... provided an AR 12-in woofer was not chosen as the "designated driver." Cheers, John
  3. johnieo

    AR-3a Recap - Is this heresy

    Hi Ligs: Caps in parallel: Add the individual C values to find total C, as you know. The max voltage of the group is that of the capacitor with the lowest voltage rating---they all have the same applied voltage, and the unit with the lowest rating will fail first. However, there is an issue if we are using electrolytic caps-- in case of electrolytic caps, one usually uses caps at some max voltage near to, but below their rated value. For example I might choose caps with a 50-V rating to use with say, 25-35 V max applied. So in the case of this max applied voltage I would likely not use an electrolytic with a 450-V rating in parallel with one having a 50-V rating, as one would operate at a very low fraction of its rating and not be formed properly. All electrolytic caps used in a parallel group do not all have to have the identical max voltage rating but should be similar-- perhaps, say, between 50--100 V for that example. Caps in series: As you and others know, the total C is found from the reciprocal rule. 1/Ctotal = 1/C1 + 1/C2 + etc. It is not prudent to ever put caps in series because there is an added complication: capacitors have leakage resistance, and it affects the way the voltage is divided between the two devices. Capacitors have large (parallel) leakage resistances. Lets for example say that we have two 100 uF caps in series. Ideally we have 50 uF total, with half the voltage across each device. However, that assumes ideal capacitors with infinite parallel resistance. Nothing is ideal in real life! Let's assume that one of the 100-uF capacitors has a leakage resistance of 2 MOhms and the other has a leakage resistance of 4 MOhms. The DC voltage across the two capacitors in series divides according to their resistance values, not their C values. So in this case 2/3 of the applied voltage would appear across the unit with 4MOhms leakage and 1/3 of the voltage would appear across the device with the 2 MegOhm leakage. Were we to apply a large voltage to these units, one of them would fail well before the other! Since leakage R can change with age, it is not wise to ever connect caps in series. So the practical answer to what is the voltage rating of series caps? Don't do it! hope this helps, john
  4. johnieo

    AR-3a Recap - Is this heresy

    "However, as much as I do like these 10 uf surplus caps and am pleased that Kent has directed us to them with high endorsement, I would be totally uncomfortable combining this many capacitors into one cabinet for a single driver - - - many of you are certainly superior to me at circuitry assembly, but this recommended scenario would be nothing short of a wiring nightmare in my hands." Hello: Wiring ten 15-uF caps in parallel is really simple as the ten can be combined outsidet the cabinet and installed as one unit. It does have one advantage. When connecting ten in parallel, the total capacitance becomes 10x15=150uF, as expected, but the equivalent series resistance becomes ESR/10. Levenson used ten small film caps in his cello amati likely for this reason--reduced ESR. That said, there is absolutely no problem with using non-polar electrolitics other than giving one's grandchildren a headache in some years. The reason most old electrolyics failed was a poor end seal that allowed water in the dielectric to evaporate. First C increases as the aluminum etches faster, then it becomes very small, as the device dries completely. The worst cpacitors were encapsulated in PVC tubing (usually black), and then end sealed with pvc (usually red). The plug did not stay sealed to its shell. The best were made by Sprague and Cornell-Dublier; both firms used a high quality elastomer with a strong crimp seal--many are still within spec (both C and ESR) thirty-five years after fabrication! Still, its a good idea to replace all at this age. Today inexpensive electrolytics are rated anywhere from 2000--7000 h. I have fixed many a modern widget for a few cents worth of small electrolytics! JohnO
  5. johnieo

    AR Restoration Meeting--1

    Do you have to be a member to get the custard pie? Nope, 80 cents will do. BTW, how does one qualify for membership in the society? Article 0 (dated 23June2013) of the society bylaws states: "membership is attained by appearing in a photo with at least one other card-carrying CSP member." Cheers, JohnO
  6. johnieo

    AR Restoration Meeting--1

    The third 2013 meeting of the AR Restoration Society was held at Wong's on Mott St. in the City. Minh gave a "chopsticks-on" demonstration entitled Selecting and Enjoying Fine Chinese Cuisine. This was followed by a "hands-on" session on how to select dessert at a Chinese bakery. This was the most popular meeting, with a 50% increase in attendance. At the suggestion of JKent, no continuing education credits will be given, lest the tax-exempt status of the Society be jeopardized. Respectfully submitted, JohnO, recording secretary
  7. johnieo

    AR Restoration Meeting--1

    The second 2013 meeting of the AR Restoration Society was held 16 June in Highland Lakes, NJ. JKent gave a fine paper entitled: Purchasing AR-4x and AR-90 in northern New Jersey. Respectfully submitted, JohnO, Recording Secretary
  8. The first 2013 meeting of the AR Restoration Society was held 15 June in Latham NY. All in attendance listened attentively while Roy C presented a paper entitiled Restoring AR Speakers Found in the Dumpster.See attached image. Respectfully submitted, John O, recording secretary
  9. johnieo

    Yesterday's Technology

    Here's a link to an article in the current issue of IEEE Spectrum that discusses yesteday's technology. Not about AR, but about its era. Enjoy! http://spectrum.ieee.org/geek-life/tools-toys/oldies-but-goodies/?utm_source=techalert&utm_medium=email&utm_campaign=091312 Cheers, John in Tucson
  10. johnieo

    Villchur's legacy

    Most of the AR community knows that Villchur left speaker research and devoted his time to the development of hearing aids. He proposed two radically new design ideas: multi-channels and the use of volume compression in channels. It is also known that he sarted Resound hearing aid company, because none of the firms of that day would accept his design ideas. Today, Villchur's two design concepts are incorporated in all hearing aids. Friday, my audiologist told me that there is yet one more unrecognized tribute to Villchur's legacy; the purchase of Resound by Danavox resulted in a name change. After Great Nordic, the parent company of Danavox, purchased Resound they changed its name from Danavox to Resound; Mr. Villchur would have been pleased. Cheers, John
  11. johnieo

    Very early Ar3a - dead mid range driver?

    Hello Tim: First, it is worth double checking to ensure that there is no insulation on the two mid wires you are checking for continuity. Scrape the end of each a bit with the side of a knife or fine sandpaper, then check again--as well, check your ohmmeter by shorting probes. If for sure it is dead, you might consider Vintage AR (Larry LaGace) / Ljlagace at aol dot com / Albany, NY / 518-869-3665 /. He has been able to repair some mids, if the break occured where he can access it. If not, I would purchase a replacement from him rather than an unknown eBay source, as he checks the output level of each driver he sells. Cheers, John
  12. As all have mentioned, Ar stuffed the early versions "uniformly." The only one I have worked on that was not stuffed uniformly was the AR-3a-Limited (the Asian version, not to be confused with the Europen Improved).) Alex Barsotti, who worked on that model, said it was not stuffed with fiberglass but with 18 ounces of the the two-diameter, red/blue polyester like that used in the improved. In particular it was to be stuffed "mainly in the woofer half of the cabinet." Who knows, there may be a few additional unique models around? Cheers, John
  13. Hello npt3: Most woods bleach lighter with age (UV exposure); walnut and cherry darken with UV exposure, so its original color would have been ligher than you see today. If you choose to bleach (not usually needed) do it uniformly. Then try the Sal Martino method: apply Danish oil, wipe, wait 24 hrs, then wet polish with 240 grit ("wet-or-dry" paper)/Danish oil, dry 24 hrs, then wet polish with 350 grit/Danish oil. Dry a day, then wax with something quality like Liberon Black Bison paste wax. I begin with light or medium walnut Watco, as the finsh darkens a bit after multiple coats. Cheers, John
  14. Chip: There is no need to remove the crossover boards. They are hot glued and gun stapled to the cabinet backside. If they were destroyed on arrival, then one would use tempered Masonite, but if so, would need to restore lettering visible from exterior. Best to keep original. Simply perform all re-wiring and component replacement through the woofer opening. The AR-3a restoration manual (in AR section of library) describes techniques that apply to many facets of restoring other early AR models. AR finishes were usually oil stained and pehaps (?) over coated with clear lacquer on some versions. Additionally, what "accidents" did your cabinet surfaces befall? Attempting to remove the original finish on an old, thin venier may not result in a surface that will take, uniformly, a darker oil stain. You might not be happy with the result. We do not feel that all pieces of furniture in a room have to be the same color, just that their styles blend. Cheers and good luck! John
  15. johnieo

    Letter suffix combos on AR's

    Steve: As you noted, the alpha charaters after the number mean a great deal, and well beyond the classics of 1970 era. Long ago you posted on the AR-18 series; I saved your notes, because I was restoring some. --abbreviated here: AR-18 great speaker, basically AR-7 in a new box AR-18s changed cabinet to bull nose design AR-18b, moved tweeter to center AR-18bx, switched to cheap woofer AR-18bxi, switched to cheap woofer and cheap tweeter There were other changes in crossover frequency and circuitry as well. I don't know how these alpha designations apply to the later series, such as 9 and 94, etc., but they are extremely important when replacing parts in the 18. A good long-term project for someone would be to list in spreadsheet format the drivers for all the iterations of AR speakers! That would require a lot of coffee Cheers, John