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mvboland

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Everything posted by mvboland

  1. @tysontom - the two speakers are indeed not consistently represented above so here they are in a more orderly fashion (both now back together): The internal wiring was identical between the two and it looks like I only got one wide-angle shot showing the potentiometers and capacitors: Let me know if there is more worth seeing! -Michael
  2. One more question for the group: What is the (or your) preferred method of re-attaching the front grilles? I presume something sturdy but not so sturdy as Gorilla Glue. I take it there were different materials used over time and these look like perhaps plywood?
  3. Thanks as always to @tysontom for sharing AR wisdom. I was led astray after going down a YouTube rabbit hole on speaker placement as modern speakers seem to be best away from walls. Instead, I should have paid more attention to item #4 on the decal on the back of the speaker: Perhaps as expected, the bass response is much improved with the speaker in that position. The frequency plot below is with a calibrated microphone at 1 meter (red line - still showing some room acoustic artifacts) and right in front of the woofer (orange line). Still lacking a home anechoic chamber but both are much flatter than the ones above. In terms of the missing screw, I do still believe that was a factory boo-boo since the sealing putty that had filled the hole was painted over (just like the screws) and the t-nut underneath worked great fine once I got a new screw. I can see how it might have been missed as it was the screw that is closest to the top of the case, almost under the overhang where the grill mounts. These have also been in the family since they were new and have not been opened or taken for repair in my memory (40+ years). I checked with my mom and she doesn't remember any service either (her memory goes back somewhat further 😉) Thanks again to everyone for contributing!
  4. I am posting separately with some lessons learned about these early AR-3s in case the summary is useful to someone else later: The components used in these early models seem much better quality than what came later: The potentiometers looked great after 60+ years with minimal oxidation. They were also not 16 ohms as advertised but ranged from 0 to about 15 after being cleaned up. The oil-filled capacitors are still working great as well and measured favorably compared to new polypropylene These were stuffed with squares of pink fiberglass which seems unusual. I looked up pink fiberglass to make sure it was not a later addition and it was indeed available in the 1950's - Owens Corning added red eye to differentiate their product - https://www.sciencehistory.org/distillations/in-the-pink The internal wiring does not match what is shown for the early serial numbers elsewhere on CSP (http://www.classicspeakerpages.net/_Media/ar-3_crossover_schematics_0.pdf). The photo above shows what I found and I have included a schematic below with the slightly different wire colors and connections. Finally, it is great to have all of the accumulated wisdom available here - thanks to everyone who helped so far both on and off line!
  5. After refurbishing the mid and hi drivers, the speakers are now back together! Thanks as always to @RoyC for his work and for collaborating on getting a displaced pole piece re-centered so these could stay all-original! In terms of other typical repairs: The potentiometers had minimal corrosion (see images above) and worked great after a little Deoxit and some dielectric grease. The original capacitors still measured as good and were left in place. In terms of how they sound, at least one of the mid-range dome glue dots had popped loose so it is not surprising that the mid-range was better after some TLC (green = pre, red = post) Not knowing how these should sound, I remain disappointed with the early fall off in bass seen above. I measured the woofer Thiele-Small parameters while it was out but have not found other measures of these very early models for comparison (sounds like really AR-1 woofers here): Similar issue with no clear comparison data for the paramaters of the assenbled speaker (measures essentially the same as before restoration): I did seal the cloth surround with the solution @RoyC devised and it made things much more airtight based on the time for the displaced woofer to return to rest (went from maybe 1 second to at least 2 seconds) but the low end response remains the same. All testing above has been done with a single speaker at a time on the floor (so they are not cancelling each other out) and a calibrated microphone connected to a DATS v3. The speakers are currently being driven by Dynaco Mark IIIs. I don't have any other full-range speakers to try with the Dynacos and also only have an AV receiver as another amp which I am not sure is up to the task for these low-impedance speakers. Hopefully an update after I test the Dynacos some more to see if they are part of the problem but any other input is welcome!
  6. As part of my AR-3 project, I was able to repair a particular issue with an early (serial number < 1000) AR-3 mid-range driver and wanted to share it in case it helps others keep theirs in service. As many here have done before, I sent my hi and mid drivers off for refurbishment. After removing the dome, the pole piece was noted to be displaced relative to the hole in the faceplate: After some helpful feedback from @tysontom regarding how those drivers are put together, I loosened (did NOT remove) the central bolt on the back of the unit which secures the pole piece to the backplate. Note that the glue used to secure those fasteners was thin and easily broken: Once that was done, I confirmed I could move the pole piece using a small screw driver. As I was thinking about what tools/shims to use to center it in the faceplate, I pulled out my set of nail setting tools, one of which fit perfectly into the notch in the faceplate. With some tapping (gently so I did not ruin the magnet!), I was able to center the pole piece: I then re-tightened the center bolt and the unit was ready to have its coil and dome re-placed: I believe the root cause here was loosening over time of all of the fasteners as none were tight when removed from the enclosure. The glue applied to the back of the driver at the factory would be expected to hold the nuts on the 3 bolts securing the faceplate to the backplate in place but I am not clear it kept the bolts themselves from rotating over time. I did tighten everything before re-gluing the nuts and bolt on the backplate. I would have preferred to use a thread locker (Loctite) but did not want to remove any of those fasteners out of fear I would not be able to get things back together. Thanks again to @tysontom and @RoyC for their time and sharing of knowledge on this project!
  7. And to compare the parameters of a new 24 uF polypropylene capacitor (which I had purchased in advance assuming it would be needed) to that oil-filled beast: New: Old:
  8. Interesting evidence of some build quality issues in these early AR-3s: - One of the screws mounting the tweeter to the enclosure was missing (so only 2 of 3 present). The screw hole was filled with the sealing putty and so probably looked OK to the builder. - One of the woofers was likely marked and installed incorrectly and then fixed before shipping. Note the red X marking the positive terminal that has been crossed off in orange. When de-soldering the woofer, I found two sets of solder connections on each terminal, one where the bare wire portion remained but had been cut off and the other (correct) wire soldered further up the terminal.
  9. As I am disassembling things, I was able to measure some of the component parameters and have included them below. Question for the group at this point - I have the woofer out but the hi and mid drivers are REALLY stuck to the cabinet. I tried pushing them out from behind, tapping the mid with a rubber mallet, and prying from the front (only succeeded in marring the cabinet!). Any tips for that step so I can send them off for refurbishment? Updates from the project since last post: The parameters for the woofer are below. This design seems unusual (not seen in photos I have found online) but I was able to find the same style at https://www.radiomuseum.org/r/acoustic_ar3.html# where they have the serial number in one image and it is of a similar vintage (mine in 900's, images from one in the 2000's): The domes on the mid and hi drivers are hand-labeled with numbers: A couple of the foam mount points on the mid driver dome have come loose (one intact, one broken below): And thanks to those who commented on the longevity of those oil-filled capacitors! They seem to be close enough to the design values to leave in place:
  10. Since I have not seen some of these components (capacitors really) in other posts, I thought I would post images here from opening the cabinet: The potentiometers are actually not bad. One of them goes smoothly from ~1 ohm to almost 16 ohms and the other looks like it needs some mild cleaning (readings are glitchy over rotation):
  11. @Ronan - thank you for the comments! Most of the surfaces are in good shape: But there are some minor scratches, worse on the top of one which served as a base for a small sculpture for some period of time: @RoyC - as a highly regarded expert on these early AR speakers, any thoughts on whether the hi and mid drivers warrant service based on the frequency response curves above? Thanks again to everyone! -Michael
  12. I recently came to possess a pair of AR-3s that my father bought new way back when (serial numbers C-0977 and C-0978) and I would appreciate the group's wisdom on how best to approach them. They are both functional with sound coming from all 3 drivers when connected to the Dynakit Mark III amps that they have been paired with for as long as I remember (amps were the last update project!). The potentiometers are functional in that there is sound from the mid and hi drivers with them turned all the way up and no sound from them when turned down but there is some "scratchiness" in the middle. The audio coming from them sounds muted in the mid-hi frequencies but I am not old enough to remember what they are "supposed" to sound like. I was able to successfully remove the front grille from one of them (have not touched the other one yet) and the drivers are not obviously damaged, unlike like some I have seen online! The cloth surround on the woofer is also intact (see attached). The woofer cone is easily displaced but returns faster than I expected based on online comments. I measured the frequency response of both speakers with all of the potentiometers turned up using a calibrated microphone (see attached). Based on all of the above, I am hoping those of you with deep knowledge of these speakers can recommend repairs. I have new capacitors for the crossovers and am prepared to clean the potentiometers. I also ordered the "special" coating for the cloth speaker surrounds. Beyond that, I am wondering: If the mid and hi drivers might warrant a tune up by one of the experts available online given the frequency response in that range seems diminished (or just update the crossovers first)? If the bass performance is as expected - it looks anemic on the frequency response curve compared to the one published in High Fidelity: Thanks to everyone in advance! -Michael
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