tysontom

ADS L1590/2 Ferrofluid Question: The question of the Ferrofluid magnetic fluid evaporating in the magnetic gap in mid-range and tweeter domes of the ADS L 1590/2 and L1290/2 is addressed in these comments below from another thread on this site, "L1590's! Now what?," and I thought it would be useful to bring it over to this topic on the 1590 that I started quite some time back, since there is much more technical information present here. I am not aware of a true problem with the voice coils in the ADS 1590 or 1290 or the other ADS models using versions of the 2-inch and 3/4-inch dome drivers; it is possible that some speakers that had been driven abnormally hard at high-acoustic levels might suffer evaporation of the oil in the gap, but under normal use this is somewhat unlikely. Comments below address this question, but the important thing is that evaporated Ferrofluid will cause distortion, lower output and uneven response, and these effects would be quite audible. —Tom Tyson Posted 14 November 2015 - 07:17 PM: Well, picked them (L1590s) up yesterday and have them hooked up now. Very, Very Nice as others have said here (TT) Impressive. I am running them with my Adcom GFA5500 and a tube preamp. My room is on the smaller side so I think that will be plenty. All drivers seem to be in good order but would like everyone's impression on weather or not I should send the tweeter/mids down to Arizona to be looked at and serviced. You can see a slight impression in one of the woofer dust caps too. --DavidDru Posted 17 November 2015 - 12:33 AM: I contacted ADS repair guru Richard So down in AZ. He think these would benefit from service to the Mids and Tweeters. Old Fero Fluid gets muddy I guess. Something you probably wouldn't realize until they are serviced and get them back and hear a difference. He has a special for all 4 for $225 that I will probably take advantage of. Posted 17 November 2015 - 05:05 AM: DavidDru, That Ferrofluid issue has become a topic of a lot of discussion. If the fluid dries up, the midrange and tweeter would likely sound distorted and "muddy," and the high-frequency mid-range and treble response would fall off precipitously. But on the other hand, if you think the sound is clean without distortion, there's a good chance the Ferrofluid hasn't dried up. I have both L1290s and L1590s, and I don't detect any distortion or change in the character of the sound, but I would have to say that neither pair of ADS speakers was electrically abused (over-driven) over time, so I don't suspect any real issue with the tweeters (or the crossovers, for that matter). In short, I don't detect too much difference from when they were new, but hearing memory is short, so it's not possible to know precisely. If you are a risk-taker, you can remove a mid-range driver and a tweeter, and you can actually remove the aluminum top plate and inspect the gap and the voice coil to see if the material has dried. The dome and coil assembly can be re-installed, but it is still a slightly risky proposition. The only real test would be to measure the tweeters' response anechoically, and that would not be easy to do without taking the drivers out of the cabinet and measuring them -- with crossover in place -- individually for on-axis frequency response to see if they match the original measurements (only a few response graphs are present in some of ADSs original lliterature). On the other hand, sending them off to be "checked" for that would mean that a new dome/coil assembly would have to be installed, and the old magnet assembly/gap would have to be completely cleaned out and replaced with fresh Ferrofluid, and that is a very, very difficult thing to do since the Ferrrofluid is a magnetic substance in an oil base, and those magnets are very powerful. In other words, unless it was done by the factory -- which no longer exists -- it's very likely that the end result could be worse than when you sent them in for repair. As they say, "if they ain't broke, don't fix them!" —Tom Tyson Posted 17 November 2015 - 12:33 AM: Ferrofluid does also reduce Q of resonance. Measuring Q or at least max impedance will take only few minutes and may give clue how things are? This is not fool proof method as coil scraping to dried fluid will also reduce Q, Best Regards Kimmo Posted 17 November 2015 - 11:04 PM: Kimmo, Yes, measuring the impedance at resonance might be good, but it would need to be compared with the original factory curve for reference to determine any changes. Does anyone have that? I suspect not, insofar as specific measurements were proprietary during the ADS production years, to my knowledge. There were generic measurements that were published, but not specific measurement curves. It's the same with the frequency-response measurement of an original vs. an old one; unlike AR, for example, there were few, if any, published response and distortion curves, per se, of the ADS drivers other than in promotional literature. ____________ ***Probably the only thing to do now would be to listen carefully to determine if there is an audible problem. If one of the speakers had been previously played at very high output levels -- especially over extended periods -- the temperature of the voice coil would be very high, and this would accelerate changes to the Ferrofluid in the gap (even cause the magnetic fluid to boil), but under normal conditions, no one seems to know how long the Ferrofluid will remain in the gap without going bad. I've heard 15 years, but that's also the "half-life" of urethane-polymer foam surrounds, so that age period for Ferrofluid is probably internet "conjecture." I honestly don't know the answer to "how long." It is clear, of course, that if new oil is put in the gap, the old stuff has to be removed, and that job is very, very difficult due to do because of the strong magnetic strength of the ADS magnets and the narrow voice-coil gap. Metal particles from the Ferrofluid would be left behind, too. I suspect that those metal particles and any oil residue left would be highly resistant to removal, so I just don't know how it could be effectively accomplished. Also, it's nearly impossible to get beneath the gap; i.e., on the underside, because of the back plate/pole piece assembly that are staked together. Therefore, all removal would have to be done from the top, and I've seen attempts at doing this, but none was definitive and the outcome was questionable. And, once all of this was done, the driver would have to be measured for smoothness, uniformity and impedance, as well as for sensitivity, and the measurements would have to be compared with the original impedance curves and response curves, for which none were published (for the public) by ADS. —Tom Tyson 11/21/2015

The time-line is almost correct: the AR-1 and AR-1W were introduced in 1954; the AR-3 and AR-2a came in 1959 and the AR-3a came in 1967. Those are the more obvious mistakes. --Tom Tyson

The reason for the 8-ohm operation was to optimize bass response when the speaker was placed unfavorably with regard to bass performance. When the AR-1 (or AR-1W) was placed in a corner or along a wall close to a corner, the use of a high damping factor (4 or 5 was fine; anything above that was superfluous) was desirable and resulted in uniform deep-bass output, and the speaker should be operated in the normal manner with the strap across the terminals #1 and #2, thus shorting across the 3.5Ω resistor. However, when the speaker was not mounted in a favorable position with regard to bass performance—such as out in the middle of the floor or along a long wall—a lower damping factor was desirable, especially if the amplifier had a switch-selectable damping-factor control, such as the early Fairchild 75-watt mono tube amplifier. Mounted unfavorably, the AR-1 could sound somewhat thin or bass-shy, so changing the damping factor to 1 would bring up the bass response to the optimal, "normal" level. Many amplifiers did not have a variable damping factor, so the AR-1 could be changed to give a damping factor of 1 by adding resistance internally in series with the woofer—by changing the straps across the input terminals. This connection was to be used only in those circumstances, and unfortunately, doing this wasted about 50% of the mid-range power of an amplifier. Changing the strap to get 8Ω operation was not intended for the sake of impedance-matching, according to AR at the time, because it was considered better to mismatch from the amplifier 8Ω tap to the 4Ω AR-1. There is no loss in quality by this mismatch, although the amplifier power in the mid-range is reduced by as much as 30%. This, too, was in the days of tube amplification, not solid-state amplifiers. Impedance-matching became very important with solid-state designs starting in the late 1960s and early 1970s. The wire in the early AR-1 crossover was a fabric-covered, plastic-insulation wire, approximately 16-18 ga. stranded copper. I'm not exactly sure when the first Aetna-Pollock controls appeared on ARs. A earlier, beefier level control (Allen Bradley? I can't recall the manufacturer) first appeared on the AR-2 and AR-1s of about 1957 or so; at least the first AR-2s always had the level control for the tweeters. The first AR-3s (and the first AR-2as) had an early version of the A-P control, so it might have been around 1959 when the first A-P controls appeared. The AR-2 was introduced in March 1957, and the AR-3 was first shown in October 1958 but not shipped until the spring of 1959, well after the AR-2. The AR-2a, using the AR-3 tweeter, also appeared at approximately the same time as the AR-3. Hope all of this doesn't confuse things further! —Tom Tyson

The early "multi-terminal back-plate" AR-1s had a 3.5-ohm, wire-wound resistor across terminals #1 and #2 that when unstrapped, would raise the impedance to 8 ohms. The 8-ohm connection was there to compensate for "unfavorable" mounting conditions, such as out in the center of a room on the floor or along the center of a long wall. Remember, too, that this was pre-stereo days, so only one speaker was being used. The 8-ohm setting changed the damping of the speaker, and it was not specifically designed to match an 8-ohm amplifier tap. Normally, the AR-1 came wired with that strap across #1 and #2, giving the normal 4-ohm resistance, and amplifier input connection was to terminals #1 and #3. For the other connections, #4, #5, #6 and #7, the normal high-frequency level was attained with straps between #4, #5 and #6. A slight increase in treble was obtained by connecting straps between #3. #4 and #5. To decrease the high-frequency level from normal, connect metal straps between terminals #5, #6 and #7. Crossover of AR-1 SN0006, showing the oil-filled capacitor and neatly installed (at right angles!) 0.4 mH coils and hand-wired resistors across asbestos pads. --Tom Tyson

Jeff, one clarification on my picture (eBay picture) of AR-1 #0696: I was mistaken, it was made in 1956, not 1955. I had forgotten that AR built exactly 455 AR-1s (and I assume AR-1Ws) during the first year of production in 1955, according to what Edgar Villchur told me. He said that number always stuck out in his mind at the time, since the company was proud of the production number. So, therefore, the #0696 would have been in 1956. As for that changeover, I'm thinking there must have been a mixture of surrounds used for awhile until it finally became 100% half-round types. Also, some early surrounds were black and some were the natural color of orange, but treated with butyl-latex. So not every woofer was coated with the lamp-black treatment. Kloss left AR after the buy-out in February, 1957. Nevertheless, he was always second-fiddle to Villchur. Villchur was President and patent-holder, so he ultimately called the shots and made all of the big decisions, so the changeover probably came sometime in that time-frame; however, I'm sure they had to use up an inventory of the pleated surrounds. By the way, all of the pleated and half-round surrounds were originally orange in color and then later painted with a butyl-latex sealant with lamp-black added. The first half-round surrounds were glued to the inside of the cone; later ones were done in the more conventional method we know today. Your AR-1W story resembles the story of the AR-1 #0006 that I got several years ago. The speaker label was hand-written in Kloss' sloppy handwriting, and the eBay seller had it as an "AK-1" instead of "AR-1," and this threw off bidders. Apparently no one recognized it but me, and I put a huge reserve on the bid and ended up winning it as the only bidder for $50. I sent the seller a shipping carton and a prepaid FedEx shipping label to get it back safely. Shipping was three-times the cost of the item itself. AR-1 hand-written label Early AR-1 (0006) woofer with sand-cast frame, all hand-made. Appearance of AR-1 on eBay was similar to this picture, and not immediately recognizable. Another early type half-round, Serial Number 1044, black Painting the surround with butyl-latex (with lamp black in this case). Natural-color surround (half-round). --Tom

Jeff, I'm not sure of the exact date or serial number of the switch-over from pleated surround to half-round surround on the AR-1 and AR-1W, but it was early in the first year of production during 1955. As it happened, Ed Villchur and Henry Kloss got into a "discussion" about which was better, the pleated surround or the half-round surround. Kloss wanted the pleated version; Villchur wanted the half-round and had shown it in his patent. The only way to settle the argument was to compare the two versions to see which had the lower distortion. The winner: half-round surround. Had there been a draw, the half-round surround would have won anyway because Villchur owned the company (well, he had 51%). Early in 1955: AR-1 SN0695. --Tom Tyson

Bill, Your egg story reminds me of a time when our daughter was an infant, my wife began sterilizing some milk-bottle nipples on the stove by boiling them in water with the burner set to "high." Meanwhile, before the water came to a boil, our daughter awoke early from her nap and for some reason, my wife decided to quickly visit a best friend a couple blocks away. Off the two of them went, and suddenly at the friend's house, my wife realized what she had done. By this time, all three headed to our house to find smoke pouring out of the kitchen and the strong smell of burning latex. The nipples were completely scorched, and the pot and lid were heavily warped. I was out of town traveling at the time, so I missed all the excitement! My wife then called the fire department and told them that it was a minor thing, but asked if someone come out due to the latex smoke in the kitchen? It was not a 3-alarm fire or anything—just send someone out to check. Of course, a large fire engine arrived with sirens and flashing lights. They put fans in the house to clear out the smoke. —Tom Tyson

Bill, Hope you didn't spread any "woofer germs" on the dining-room table. From afar, someone might think you had some special black-glass (onyx, perhaps) serving dishes. It might surprise visitors if some food object were placed on those cones, and you applied a quick, transient pulse to the woofers, sending that "something" into the air -- letting one's imagination run wild, of course. It reminds me of my youth. When I was in school as a young boy (I went off to school for a few years in my early youth), a group of us at one of the dinner tables (before the headmaster arrived) put small pats of butter on the handle-end of a fork and pounded the butter up into the air -- with the hopes of having it stick to the ceiling. The ceiling in this old building was at least fifteen feet up, and getting the butter up there took enormous fist power. As the heat built up in the building, the butter would slowly melt, and small droplets would sometimes land on the table or even on the headmaster's head -- our mischievous intention. This practice (along with spitballs in study hall) stopped pretty quickly after that, however, and since this school had a strict honor system (caught lying, stealing or cheating you would be dismissed), several of us got into big trouble. None of this is related to the Allison IC20 woofers, of course! --Tom

Bill, Those are great images of your IC20 restoration project! The woofers on the dining-room table look like preparation for a Thanksgiving dinner or something! Is the woofer/voice coil picture one of the IC20 woofers with replaced spider and surround? Who did that work? I'll look for those Chicago CES pictures. I have a lot of print folders to search, so it will probably take awhile. Thanks! --Tom

Bill, I will definitely look for those pictures taken at the Chicago CES. I'm not positive I took pictures of the IC20s, but I'm pretty sure I probably did. I usually photographed everything of interest (and continue to do so to this day with digital imaging). The key word in your message above is "hand truck." In this business, you can't be without one when it comes to moving these big things around. Well, in any event, those IC20s are in great hands now, and I know you are happy with them! Did you end up refoaming the woofers? --Tom

Bill, How did I originally miss this story? That is fascinating, and to think you chanced upon the very first pair! I'm pretty sure that I have heard your very IC20s, because they were probably used at the Chicago CES by Roy and Sumner when they were introduced. I might even have a photograph somewhere. I distinctly remember hearing "Bach on Wood," an analog CD played on them, and I was amazed at the sound. The price (despite being able to get them at probably half-off) was high at the time, and I had just purchased another set of speakers (ADS L-1590s), not to mention being somewhat "speaker poor." That was the only reason that I did not purchase a pair of IC20s. Obviously, you had to travel somewhere to pick them up, no? --Tom

Bill, I would blame you one iota for not wanting to part with that tweeter even for a test. For one thing, sine-wave testing, or white-noise testing for that matter, is stressful on any driver -- even with short-term tone-bursts -- and like you, I wouldn't want to do anything like that. Your remedy to use equalization to bring up the treble is probably -- by far -- the best way to handle any attenuation in the treble, even if that is necessary. Save that tweeter. Another thing: the treble dispersion on the IC20 is so outstanding that the integrated acoustic-power output is better than almost any other speaker, and therefore the high-frequency output into the reverberant field would more than offset the slight attenuation that might be occurring at the frequency extremes! Yeah, perhaps that last half-octave in the 15-20 kHz region is down a bit on axis, but the power response is probably ruler-flat out to at least 15 kHz, so what's not to like about that! There are any number of exotic speakers with great "imaging" and ruler-flat on-axis frequency response in the direct field that would fall flat (no pun intended) trying to put energy into the reverberant field. Poor off-axis performance assures that a directional speaker that sounds "spacious" and "3-dimensional" in the direct field, toed-in pointing to the listener a few feet away, will almost always sound dull and lifeless once that listener moves back into the room's reverberant field. It is amazing how much poor dispersion affects the overall performance of a speaker! Some speaker companies think that they can use a directional (read: "large-diameter") midrange driver and a small-diameter dome tweeter and solve the dispersion problem, but this isn't true. Much of the power response energy is in the midrange and lower treble. I would love to learn the story on your IC20 acquisition. Where did you find them and so forth.... --Tom

Bill, you figured out what you needed to do to maintain the "Omni" settings without having to go in and try to rebuild the entire circuitry, and that makes sense. Just set it to the Omni position and unplug the power module; problem solved. I had forgotten that the IC20 did not use Ferrofluid in the tweeters, but rather used silicon grease. Roy Allison used this with the AR-6 tweeter as well some other AR versions, but the examples I have here show no sign of deterioration of the grease. Roy did tell me that excessive power could easily "boil" the grease, allowing it to work its way out of the gap or worse, harden, but I think this would be quite uncommon. The grease probably does change slightly in viscosity over time, however, and this might cause output problems with the tweeters at high frequencies. I would love to see a comparison of the tweeter output with your NOS 1988 tweeter and one that has been in use for many years. The big question might be if there is any truly significant change in output over time. Maybe you could get DRM or someone to compare that tweeter (if you wanted to chance such a test, which always makes me nervous) with an existing one that he might have. I've got a LinearX LX500 system on order—it's only been on order for the last 4 years—and if it ever gets here I'll let you use it to compare the two with some definitive measurements. —Tom

Bill, I think you are quite right about Howard's system. The electronics went south, and he couldn't get a reliable fix. BTW, how do your electronics work at this point? Have you had to intervene, or have they "stayed the course" and given you reliable service? Once he had changed his system, he went on to other things, such as changing the woofer configuration from push-pull to conventional, and then he did other things. Overall, his 20s still look like 20s, except for the lights on the front, but changes lurk underneath. I actually think he has toyed with the idea of changing the drivers to some degree, mainly because of his fear that the Ferrofluid has dried, causing attenuation in output in the treble. He did go in and change the crossover somewhat to compensate for the lost output. —Tom

Bill and Phil, Well, I do tend to tweak on Howard; I've known him for many years, and he knows that I kid around with him quite a bit. As for his IC20s, they are certainly in mint condition with nary a scratch or mark of any kind on their cabinets. In Howard's case, they are an integral part of a surround system, and he is constantly experimenting with the spectral balance, and I think he has moved to more of that "focused" mode to give him less of a diffuse image, I suppose. If he were using them only for 2-channel stereo reproduction, then I doubt he would have tampered with them so much, but now he's completely into the modifications to suit his surroundings. He doesn't rely on the excellent woofers for bass reproduction (he uses two big subwoofers), and now he doesn't like the very wide dispersion of the panel arrangement, I suppose. When I listened to the IC20s for the first time at the Chicago CES in 1987, I heard them operated in their different operating modes just briefly, but the Omni mode was clearly the best for me. —Tom

Bill, Those are truly pristine, easily the best-looking pair of IC20s I've seen. Howard's IC20s are also nice and in mint condition, but he's heavily modified his pair with crossover changes, removal of the push-pull woofer configuration and removal of the remote-control setup, including the indicator lights. Somehow, they are not IC20s any longer. —Tom

Bill, I'm with you on this site. It is stable, reliable and organized. Hope others from Yahoo join in as well. BTW, your Allison IC20s look beautiful and "like-new." It's good to see a pristine pair that is completely original. Could you post some other pictures of the speakers? —Tom Tyson

How about the AR93 and AR94? Both of these speakers—from 1980—were true 3-way, 8-inch designs, but granted, these were not conventional 3-way designs in the sense of the AR-5/3a, etc. These were floor-standing models with 3-way crossovers, using the updated, Ferrofluid version of the 1¼-inch tweeter. These speakers were "parts-bin" engineered speakers using conventional drivers that took advantage of new thoughts on boundary issues (the "Allison Effect"), giving pretty solid bass down to the low-40Hz range (-3dB of 44 Hz), and these speakers were relatively inexpensive and could sound impressive if placed properly. The crossover frequencies were 350 Hz and 2000 Hz. —Tom Tyson

The first series of the AR-10/AR-11 tweeter was yellowish-orange in appearance, and it did not have Ferrofluid in the voice-coil gap or the adhesive-back foam piece on the front of it. It was plain. The performance of these tweeters should be unchanged over the years, as there is no urethane-foam suspension (as in the AR-3a tweeter), and there is no Ferrofluid that can dry out over time. This first series of the AR "Advanced Development Division" (a name taken after Lockheed Aircraft's original "Advanced Development Programs," later known as the "Skunk Works"), introduced in 1975, included the AR-10π, the AR-11 and the AR-MST. In 1977, these speakers were updated to the "B" series with new models added and changes to the logo and the addition of the Ferrofluid-cooled drivers. These tweeters were characterized by the black domes -- original versions were plain -- and around 1978 a foam pad was attached to the front of these tweeters. The AR-11-type tweeter is a excellent driver with excellent overall performance. It is more efficient by several dB than the AR-3a hard-dome tweeter, but it does not have quite as good dispersion as the 3a tweeter. Therefore, the on-axis output of an AR-10 or AR-11 tweeter is greater in the high frequencies than the AR-3a, and the spectral balance is slightly brighter in the high frequencies, but the AR-3a has slightly more extended acoustic-power output due to its better dispersion. —Tom Tyson AR-3a-vs-AR-11_Tweeter_ARHPG_001.pdf

The ADS L1590/2 Owner's Manual is attached —Tom Tyson ADS_L1590-2_Owners-Manual_Tyson980.pdf

Attached: 3-tweeter AR-MST Crossover Schematic. --Tom Tyson

The Acoustic Research AR-12 Crossover Network --Tom Tyson Acoustic Research_AR-12_Crossover_ARHPG_12.pdf

Oops. Yes, I meant to say "Amplifier," not "Turntable." Thanks for your clarification. As for the phone jack output and switch on the amplifier, I suspect that AR made that change on all models after a certain date, but I'm not certain of that time period. Originally, it was felt not to be needed and to keep costs low, but I think the demand for it was there all along, and some reviewers commented on the absence of it on the amplifier. Once the AR Receiver was introduced, the headphone jack feature was included, of course, so probably after that time it was decided to push on with it. Delrama probably pushed for it for the export market; many foreign listeners insisted on headphone compatibility. AR did, however, have an early "fix" for it, but it involved adding a little switch box, wiring and so forth -- after the fact. As mentioned earlier, the AR Amplifier was introduced in 1967, right at the beginning of Teledyne's presence at AR. The AR Receiver was introduced in 1969; the AR Tuner came in 1970. These dates would be coincident with a change to the newer Trajan script "AR" without the "Inc." So, I'm thinking that the AR Amplifier soon followed the change made in the Receiver and Tuner to use only the "AR." Perhaps the headphone jack was added at the same time the silk-screen change was made; it would make sense to do it all at once. The AR manufacturing and design facilities in Amersfoort, Holland was opened in 1969; the facility in Bedfordshire, England was opened in 1971 about the time of the introduction of the AR-LST. With these facilities, there was actually less need for export outfits like Delrama, and I'm sure that company was phased out around this time anyway. The Delrama outfit was close to the original stalwarts at AR; i.e., Edgar Villchur, Roy Allison, Abe Hoffman, Gerald Landau and so forth. The AR-11 "Visible" speaker was made available to AR dealers in the mid-1970s as a sales tool, and quite a few were made. I'm glad I held on to mine! There are probably a dozen or more still out there, but I've never seen one show up on the internet. --Tom Tyson

Some additional technical details on the ADS 1590 Series-2 woofer, part number 206-0631. The images have inscriptions describing mechanical details. 10-inch acoustic-suspension woofer designExtremely flat, linear response in the 28-350 Hz rangeVery low distortion from 20-350 HzLow-resonance [free-air resonance approx. 19-20 Hz]Low system resonance 35 Hz; -3dB 28 HzTrue system extension to 20 Hz and below with low distortionADS Stifflite molded-fiber/paper cone assemblyCrossover at 350 Hz2-inch copper voice coil wound on Nomex high-temperature former (bobbin)Large-diameter, flexible treated-fabric spider assembly for long excursions and voice-coil centeringButyl-rubber half-round surround (skiver) for precise control and long-life durabilityLarge voice-coil overhang, keeping voice coil in linear magnetic field during >1/2-inch excursion--Tom Tyson

Delrama was an export company that represented Acoustic Research during the 1960s and perhaps into the early 1970s. Delrama was not an AR-owned company or in any way affiliated with AR. Delrama simply represented AR abroad. AR products and service-replacement parts were handled by Delrama, and the company took responsibility of shipping, selling, displaying and servicing AR products into Europe (and perhaps other areas) during much of this period. In the early 1990s, Edgar Villchur called me to say that the owner of that export company was shutting down business and had a supply of service parts left over that he wanted to dispose of, and that these parts included crossover networks for AR-3s, AR-2axs, AR-3as and so forth, as well as service parts such as drivers. Included were several AR-4 woofers that were mounted inside a plywood shipping carton screwed together for protection, AR-3 tweeters and so forth that were also in those cartons. I contacted this individual, and I found out that he also had one of around three or four original AR-3a "cutaway" display speakers (actually fabricated in Cambridge by Sumner Bennett) that had been to Europe and back a few times for audio shows and military export shows. I offered to buy most of his old inventory -- which wasn't a great deal -- and the AR-3a Cut-A-Way (picture attached). Except for one AR-3 tweeter I sold, I still have the inventory. The price was extremely reasonable, and the products were shipped to me. I had both the AR-3a Cut-A-Way and the AR-11 "Visible" speaker on display at the 1994 AR 40th Birthday Celebration in Grand Central Terminal in New York. Both speaker were fed with a 5 Hz sine-wave signal to show the woofer pumping slowly back and forth much like the demonstrations in the AR Music Room back in the late-50s and 60s. There was an AR-3 As for the phone-jack output on the AR Turntable, I don't know the details on that iteration, but I suspect it was done for the export International market during the latter part of production. It may have been available here, but I suspect it was intended for that market. I don't have any details on that unit, but I might ask my friend Sumner Bennett (he was sales manager for AR for many years) if he remembers any details on it. The fact that the Trajan-script "AR" logo did not include the "Inc," makes me think that this update came after the June, 1972, Teledyne acquisition of Acoustic Research; after that time, the "AR Inc" morphed into "AR," without the incorporated at the end. This marked the end of the "classic" period for Acoustic Research, and a year later AR moved from Cambridge to Norwood and soon the "Teledyne AR" period began. The difference in the back panel heat-sink portion of the AR Amplifier was the result of updates to the original design. The heat sinks exposed on the rear are the newer iteration (also most with the improved biasing network for better reliability), designed for better cooling. It was felt that the perforations obstructed the convection cooling of the output devices, thus it was improved. --Tom Tyson