Later model AR-3 woofer and crossover update

[Guest Jeff W.]

Greetings All, You'll see this is my first post having lurked here for a few months. Thanks to everyone for the wealth of information! Naturally, I'm starting with some questions. I bought a pair of later model (serial #70255 & ?) AR-3's at a moving sale and am in the early stages of restoration. One has the aforementioned serial number and the other's was torn off, but has the exact same drivers and crossovers. The woofers have stamped steel baskets, large (round) ceramic magnets, and foam surround with the 1/8" thick masonite ring under the outer portion of the surround. They are either the "A.2" or the "A.3" as described in the AR-3a restoration manual (thanks to all involved!).
That brings me to my first question: did the later model AR-3's use this woofer? If not, can it be used as a direct replacement in the AR-3? My other questions concern the crossovers. I am attaching photos of the mid/tweet and crossover. The mids are treated cloth domes (A.12?) and the crossovers appear to be exactly as shown on the schematic for the AR-3 in the library. I plan to update/replace the caps in them with metalized poly as is universally recommended here. I have purchased two 6.2uf +/- 3% 400v Solens and one 24uf +/- 5% 400v Solen for each. As I've also seen recommended, I have purchased a .33 ohm resistor to place in series with the cap for the tweeter. Am I good to go with these or are there other things I need to consider, such as changes due to the woofer if it is not a direct replacement. Thanks in advance, Jeff

[RoyC]

Welcome Jeff,

Based on my experience, you would probably be happier with the cloth surround alnico magnet woofer (A.1 in the AR-3a document) in your AR-3 system. The AR-3 and early AR-3a were equipped with that woofer, and had correspondingly different crossovers than the later AR-3a. It appears that your woofers (and possibly your mids) are later replacements. Until you can find some alnico woofers, however, it can't hurt to complete your restoration and use them as is. I'm a not aware of any AR-3 crossover modifications associated with the ceramic magnet woofer.

Good luck with your restoration.

Roy

[Guest Jeff W.]

Thanks Roy. Did no AR3's come with the ceramic magnet woofer? I know the 3a switched to the foam surround (A.2) in 1969 according to the AR-3a manual and that the AR-3 continued in production after the introduction of the 3a. Were the AR-3's all produced with the alnico woofer until production ceased? As for the midrange, it is my understanding (Tom Tyson) that after serial #70228 the AR-3 was produced with a modified 1-1/2" cloth dome mid from the 3a. Was it only the A.10 version that was used for this purpose and no others? I know the crossover point is higher from the woofer to the mid in the AR-3. I assume there is no harm there, but in using the 3a mid that I currently have can it safely reach the 7500 Hz crossover point to the tweeter of the AR-3? I see the AR-3a crosses at 5000 Hz. Thanks Again

[RoyC]

Thanks Roy. Did no AR3's come with the ceramic magnet woofer? I know the 3a switched to the foam surround (A.2) in 1969 according to the AR-3a manual and that the AR-3 continued in production after the introduction of the 3a. Were the AR-3's all produced with the alnico woofer until production ceased? As for the midrange, it is my understanding (Tom Tyson) that after serial #70228 the AR-3 was produced with a modified 1-1/2" cloth dome mid from the 3a. Was it only the A.10 version that was used for this purpose and no others? I know the crossover point is higher from the woofer to the mid in the AR-3. I assume there is no harm there, but in using the 3a mid that I currently have can it safely reach the 7500 Hz crossover point to the tweeter of the AR-3? I see the AR-3a crosses at 5000 Hz. Thanks Again

Good questions...I have much less experience with the AR-3 than Tom does, but I don't think there were any manufactured with the ceramic woofer, or the mid with the diffuser dot under the center of the metal grille. The switch to the foam surround woofer in the 3a occurred extremely late in 1969. Several of the oldest AR-3 to 3a conversion cabinets I have seen date to 1970, so it is hard to say what AR may have done with the last AR-3s. Anyway, my experience suggests that the woofer will likely result in a bigger difference than the midrange in a late AR-3.

Roy

[Carlspeak]

Jeff:

Make sure you open up those rheostats and inspect them carefully if you haven't already. You seem well aware of the restoration document. It has some great tips on dealing with corodded pots.

Good luck with your project.

[Guest Jeff W.]

Roy, If I'm not mistaken, I've seen the AR-3 listed as late as the 1971 AR catalog. As for my woofers, the physical evidence would indicate that they were replacements since there were leads that were cut off on one set of terminals when I opened them on both. The mids, however, don't look like they've been replaced. The paint and tape over the leads look undisturbed, as does the terminal block. Maybe Mr. Tyson will see this thread and be kind enough to shed a little light.

Carl, Yes, I will clean and replace the pots if needed. Thanks for the reminder and supplying some of my restoration needs!

Best Regards,

Jeff

[tysontom]

Jeff,

I believe that your AR-3 with SN 70255 would have been built close to the end of AR-3 production, most likely in early 1972. The last of the production run for AR-3s was at the end of the summer of 1972 according to the data I have, and the serial numbers would have been #70608 or somewhere close to that number. Between July and the end of August 1972, only about a half dozen AR-3s were produced, depicting the end of production.

I think that most of the AR-3s were produced with the Alnico woofer, but it would depend on the stock of parts available towards the end of production, as that woofer was also used on the first AR-3a series from 1967 up until 1969, at which time the new stamped-basket, ceramic-magnet version came into being. The AR-3a was selling at a brisk volume during these early years, so quantities of the Alnico woofer could have been absorbed for 3a production. Some stamped-basket woofers with the foam-rubber damping ring have appeared on eBay, and this variation may have been used with the last of the AR-3 woofers, but I don’t know this for sure. The foam damping ring served a specific purpose in the AR-3: it smoothed the upper-bass response on the Alnico woofer. The new stamped woofer had a low-vacuum asphalt-pulp cone that had much better internal damping, and thus didn’t need the damping ring. The AR-3a also had a much lower crossover frequency than the AR-3, so perhaps the damping ring was deemed necessary to use with the AR-3. However, I have never seen an AR-3 that came new with the stamped woofer, but that doesn’t mean that the stamped woofer was not used with the last of the AR-3s such as your models. As for using the stamped-basket woofer in the AR-3, you can certainly do this, but as Roy said, the original-style woofer is probably better suited for the AR-3 with its 1K crossover.

It is also true that about the time your AR-3s were being produced, AR had essentially run out of the old 2-inch phenolic-dome midrange. Production had ceased based on what I perceive to be AR’s estimate of production runs for the AR-3 and the introduction of the new AR-3a. Therefore, the parts were gone before the end of regular AR-3 production, so AR began to use a modified AR-3a dome (the A.10 version) that was more compatible with the 7500 Hz crossover to the 1⅜-inch AR-3 dome. The midrange version that you have in your AR-3 is the regular AR-3a version, which is basically compatible as far as efficiency and impedance. The problem is in the linear operating range or piston band of the standard AR-3a midrange driver, which had been optimized for a range of 500-5000 Hz. The modified AR-3a driver (along with the changes to the crossover) was designed to operate more efficiently up to the 7500 Hz crossover of the AR-3.

I hope this information helps a little bit. Try to find the Alnico woofers, if possible, and the modified midrange units. What you have will certainly work fine, but will be compromised somewhat compared to the original-type drivers. The most important thing is to be sure that your crossover capacitors are in spec and that the level controls are in good condition, and you can probably live with the other slight anomolies.

--Tom Tyson

[Guest Jeff W.]

Tom, Thanks for your response. I was fairly certain that the woofer was suspect. I was more unsure about the mid because, unlike the woofer, it appears to be undisturbed. If it was replaced I think it was done at the factory since it has all the appearances of being such, but I guess that would be odd too for them to use the incorrect driver. That is still a bit of a mystery to me unless it was the only available mid at the time. I was suspect of the crossover point to the HF driver.

I have been forging ahead with my restoration of the crossovers and drivers. I am nearly finished with the second speaker. I was lucky in that all the pots were in great shape. I had been so into it that I had forgotten to check back here in a while. I'll see if I can scrounge up the original drivers over time. I hope to be listening to the pair this weekend. I'll restore the cabinets in the coming spring.

I have a pair of early AR-3a's in the wings. They have the alnico woofers, but I don't think I want to sacrifice them for the AR-3's. The 3A's have all their original drivers so I think I'll keep them that way, although it is tempting to swap the woofers and get some #7 inductors for the 3A's! I'm curious to hear how the two models compare.

As a footnote, I had to do some soldering on the aluminum leads for the tweeters. It wasn't easy, but I was able to do it with a special flux paste (more like a gel) for aluminum from McMaster Carr Supply. This flux allows you to use standard, solid core tin/lead solder successfully on aluminum. The part number is: 7696A2, 4-oz. Jar Each $9.65. Their website is Mcmaster.com. If any are interested remember you need to use SOLID (no flux) core solder and it shouldn't contain silver or antimony which will react with aluminum.

Kind Regards,

Jeff