RoyC

arken, The AR-3 tweeter held up better than the first two versions of the AR-3 mid. It is also much more available, having been used in the popular AR-2ax (first version), so your tweeters shouldn't be a problem. On the other hand, finding decent non-3a type AR-3 mids anytime soon will be very difficult. You are likely in for a very long, and ultimately costly, wait. If I were you I would go with a pair of AR-3a or later mids and use AR's .4mh coil/30uf cap modified crossover as mentioned above. I have not done any careful listening comparisons with the earlier versions of the AR-3, but I have made this repair a number of times for other people and it sounds quite good...certainly much better than any AR-3 with a typically degraded/non-restored earlier mid. Bear in mind, use of the later AR dome mid simply converts your speakers to a later version of the 3. They would still be considered "AR-3". If by some miracle, you were to find a couple of worthy earlier mids down the line, it would not be difficult to convert your speakers back to original. I have a hunch, however, you would not find it necessary to do so. The LST is not without issues (four typically degraded tweeters in each cabinet). They often start at $2500+/- a pair, and shipping them is an absolute nightmare. The last two restored pairs sold by "Vintage AR" went for $4000/pr. It is probably best to stick with your AR-3 project for now. Roy

Pete, Earlier front-wired 3a mids measure below 3 ohms. Later back-wired mids through the AR-9 typically measure 3.2 to 3.5 ohms. (Your AR-11 mid seems to be a bit on the high side.). Two later back-wired AR-5 mids I recently measured were both 5.2 ohms. All the AR-5 mids I've measured in the past have been around 5 ohms, with earlier front-wired specimens, like the 3a mids, being on the lower end of the range. I estimated the series resistance on the high side primarily because the white dot/"normal" setting of the AR-5 mid pot is nearly 50% off maximum (around 6.5 ohms in series), so there is plenty of output to be had with the AR-5 mid. The prudent way to go would be to measure dcr and add enough series resistance to the intended low impedance mid to achieve 5 ohms. This would put it well within the desired spec. It should also be noted that the original "15 ohm" pots can vary by as much as .5 to 1 ohm one way or the other, and should be measured as well. Roy

Yes...and all of the LST-2 drivers are the same as the AR-5 drivers. Roy

Sure, a 2.5 ohm resistor in series with an AR-3a mid will bring it very close to an AR-5 mid. Roy

Yes, they are constructed very differently. The AR-3 mid is essentially a large version of the orange phenolic dome AR-3 tweeter (foam suspension blobs, aluminum voice coil wire, etc). The 3a and 5 mids have more modern construction with a cloth dome/rolled cloth suspension, among other differences. Roy

Hi guys, I've been repairing the AR-3 mid, not the AR-3a/5 style mid. Roy

I experimented with lots of materials, including that family of adhesives, Pete. It dries to a stiff rubber-like state (much worse than the Permatex materiel discussed above), and it unacceptably changes compliance and mass. "Might have to thin it" would be an understatement if it were to work at all. :) Roy

Thanks, Jeff...but based on our past dealings in other matters, I have nothing on you in the "unselfish" department. I will, however, take you up on that beer. Roy

I'd like to meet this Roy guy and give him a piece of my mind. He's been unable to repair a number of AR-3 mids recently sent to him! There are some really nasty mids out there. Hey Glenn, I am planning to attend the September gathering. I really enjoyed meeting you, Robert, and Pete (finally!)...and that AR-3 pair of yours is something special. Your attention to detail is extraordinary. Roy

Yikes...thanks, Pete. It is .4mh. I will correct it in the original post, so there is no confusion down the line. Roy

More specifically...the addition of a .4 mh parallel coil to the 3a type midrange, and the addition of a 6uf to the 24uf mid capacitor to make 30uf will make an AR-3 the same as the last version of the model. See the Library section regarding AR-3 schematics. http://www.classicspeakerpages.net/library/acoustic_research/original_models_1954-1974/original_models_schematicss/thoughts_on_ar-3_schematics/thoughts_on_ar-3_schematics.pdf It is the last one on page 2. Roy

ctjetta, As of today, Larry may have one AR-5 mid with a broken faceplate. That seems to be it for the foreseeable future. Reply to the PM I sent you a couple of days ago if you would like to discuss other options. Roy

The HiVi replacement is not used in the AR-4 series. I agree, the Midwest tweeter is an attractive option. Based on some experimentation with the similar AR-12 tweeter, a coil of around .07mh would be a reasonable starting place. Roy

+ $11.75 shipping (to NY).

The Midwest tweeter is as viable as the HiVi replacement tweeter/coil combo sold by Larry if it is used with a parallel coil. Unfortunately, it is only available at a shipped retail price of around $80 each through Midwest, so there is no profit to be made for Larry to re-sell it. With that said, it is very well constructed, fits the cabinet hole perfectly, and it is worthy of experimentation if cost is not an issue. I will be working in Larry's shop on Wednesday, and will take a look at his inventory. Last I looked he had very few AR-5 drivers. Roy

I agree, Steve. In fact I actually prefer the AR-3a over the AR-11 and 10pi, as I personally find them to be a bit harsh in the mid frequencies...not an acceptable trade-off for me. I would only add, however, that I have experimented a great deal with tweeters in the AR-3a. More powerful tweeters (crossed over at 5000Hz) may be somewhat helpful but also increase sibilance. In my experience they do little to improve the lower frequency issue under discussion. On the other hand, as you have suggested in the past, some treble controls can be beneficial if their influence reaches low enough into the mid frequencies. Unfortunately better controls found in higher quality preamps often affect only the highest frequencies, and are less beneficial. Discussing speaker nuances and characteristics is what we enjoy doing here, but in the end the popularity of the 3a spoke/speaks for itself. Roy

Interesting thread, Aadams... I have nothing to add of a technical nature, but subjectively there is no doubt in my mind that the reproduction of vocals is not one of the 3a's better attributes, regardless of iteration. This is based on having heard hundreds of 3a's along the way. Below is a Consumer Reports review of the 3a. My guess is their opinion was based on subjective impressions of vocal heavy popular music. I don't agree with the conclusion regarding the 2ax, but there is something to the 3a's midrange response issue. Roy

Hi Klaus, To be clear it is not fuses in general causing the problem, only old degraded slow blow fuses. You would know it if you have one causing the issue described above. The problem is obvious...there is literally no bass response. The fuse is no longer usable. We now replace all original LST slow blow fuses as part of any repair or restoration. Roy

Mark, Which thread do you want to discuss your woofer issue in? I've been responding in the one you started. http://www.classicspeakerpages.net/IP.Board/index.php?/topic/10041-restoration-stopped-at-woofer/&page=2 You are receiving essentially the same information in both threads. Roy

Hi Michele, You're welcome...I'm glad it turned out to be the fuse issue, and not something more complicated. Sure, you can use them with the fuse by-passed, if you are careful about very high volume levels. Roy

Michele, Try by-passing the fuse on the back of the cabinet. On three separate occasions, I have found deteriorated slow blow fuses to cause this issue. About three years ago, upon completion of a restoration of a very nice pair of LST's, Larry Lagace (aka "Vintage_AR") and I spent a number of hours trying to figure out why there was virtually no bass response from one of the speakers. After replacing the woofer (twice) and carefully testing the crossover (the caps were new) we were still stumped. I finally by-passed the fuse simply because there was literally nothing else left to evaluate, and there it was! The difference was not subtle! Since then we have run across 2 other LST's with the same issue. It is advisable to replace those old slow blow fuses as part of any LST work and/or evaluation. Btw, Most all of the crossover series capacitors of old AR speakers are on the negative side of the crossover circuit. I believe it was originally done to accommodate the 3 input terminal/jumper arrangement. Let us know if by-passing the fuse solves the bass issue. Roy

A 25 ohm resistor is wired across each driver equipped with an 8 ohm L-pad. Page 15 of "Restoring the AR-3a " in the CSP Library shows placement in a schematic. Roy

I'm with you guys. It is hard to imagine how many people have been duped by this publication over the years. Expensive nonsense... Roy

That is the resistor (nichrome wire)...the heart of the pot. It can sometimes be deformed, but it doesn't usually cause sound issues. It is also not prone to the corrosion found in other areas of the pot. Roy

Hi Robert! Of course I just posted not to bother with the riveted disk. ...but, based on the photo in your post, it appears it may be worth the effort if there is a very good disk to work with. Roy