RoyC

All AR tweeters + side is on the left as you face the tweeter. The + lead is crossed over the other lead to the right side under the tape and soldered to the center terminal (of front wired models). Roy

There is some resemblance to the TSW era AR models. See photo of a 610 tag.

Agreed. I have experimented with that dome assembly in the past. At the very least, the crossover would have to change for it to work properly. Additionally, setting the dome without shims is risky, and he did not provide a resistance (dcr) reading. Andre...In your previous post I didn't notice you were referring to wire thickness (mm) and not value (mh). Wire thickness is usually expressed in "gauge". For example, the original AR coils were 17ga, and by the time of the Limited it was 18ga. It's good to hear everything went well. Roy

Hmmm...post a link. I would be interested to see what this person is doing with the tweeters. " I used 1.15mm now, closest i could find." For what? Obviously that value won't work for anything. I assume you meant you removed some wire from it to make the proper value? Later AR-11 and 10pi cabinets used 11 ounces of dense audio grade polyester. The earliest AR-11 used 20 ounces of fiberglass stuffing. The Tonegen woofer had a slightly stiffer suspension, resulting in a somewhat higher Fs/Fc. With the guidance of Ken Kantor, we conducted many measurements of various amounts of both types of damping material when we put together the Library's 3a restoration guide. As long as you are in the general vicinity of the above amounts you will be ok, as small variations did not make a significant difference in performance. Also, bear in mind that a refurbished woofer will not measure the same as it did when it was new. Roy

First of all, the coil on the back of the tweeter should be .16mh not 1.6mh. Don't worry about its resistance...which is dependent on the gauge of coil wire. The 2.6mh woofer coil of the Limited simply replaces the 2.85mh coil of the original 3a. As I mentioned above, just deal with the tweeters and the woofer caps and you will be all set. Roy

There is no measurement. Just line it up with the edge of the basket. Look at a woofer with an intact surround and you will see where it should be.

The friction of the shims holds the woofer cone at varying heights of your choosing. Along with properly orienting the surround, it makes it easier to install. Most modern replacement rubber surrounds are sold for subwoofer and automotive applications. They are heavier and less compliant than those used for AR woofers. I've never been aware of any rubber replacement surrounds sold for AR speakers.

Regardless of location it does not matter any more than it does for capacitor or resistor leads in a passive speaker crossover network. Driver and associated circuit polarity is the only consideration.

I'm not sure I understand your question. Like the non-polarized capacitors in your crossovers, the coil itself has no polarity to be concerned with. Just connect each lead to the + and - tweeter leads. It doesn't matter which coil wire is connected to which lead. This can be done anywhere between the pot to the tweeter.

You will still need to use a parallel coil for the tweeters, whether you use L-pads or original pots. It is not just a matter of overall output. It is about taming the tweeter's influence on the mid frequencies (ie. the slope of the crossover). If using original pots stay with the 6uf cap, and add the .16mh coil. If using L-pads, add the coil and reduce the cap to 4uf. The Limited's slightly smaller woofer coil worked in conjunction with the smaller parallel mid coil. To answer your question...a smaller coil in series with the woofer increases its contribution to the mid frequencies. The reason for the coil changes probably had to do with decreasing the load on the midrange at somewhat lower frequencies, and having the woofer compensate for the difference. Staying with the original 3a values will work satisfactorily. Roy

No iteration of the 3a used this resistor arrangement. Obviously, whoever rebuilt the crossover substituted the pots with this. I'm not sure I understand your description, but if it is as you suggested, 12.5 ohms in parallel with the tweeter and mid, it would be similar to the pots being set near maximum. When the pots were set to maximum they provided 15 ohms in parallel, and no series resistance. The primary reason for the harshness is that the Tonegen/AR-11 type of tweeter absolutely requires a crossover change to keep it from producing too much output in the mid frequencies. A .16mh coil and 4uf cap were used in the 3a Limited (along with 8 ohm L-pads.) The bundled 133uf woofer caps shown in your photo don't have a strong voltage rating for the woofer circuit. I would replace them, and simply go back to the original value of 150uf. The 3a Limited retained the original 150uf cap value and a slightly smaller 2.6mh coil with the Tonegen woofer. The 3a Limited's Tonegen midrange crossover was also slightly different from the original 3a, having a .7mh parallel coil instead of the original .88mh coil. Roy

Part of the problem is that the Improved crossover is buried in glue (see attached photo). Since there are no pots to clean or replace, and the switches are typically ok, there is an understandable reluctance to dig through the mess unless there is an obvious issue.

The AR -11, AR-3a Improved, and the AR-3a Limited tweeters are all wired with reverse polarity to that of the woofers. I believe the wiring of the mid of the AR-3a Improved has never been conclusively determined. I have two schematics, one showing the Improved mid wired in phase and the other out of phase. Roy

It is not likely for putty to have been originally used with this generation of AR speaker. Given the absence of level controls someone has obviously modified this pair, so any putty you find will not be original. Roy

The crossover of the 3a "Improved" departed from the original design more than any other version of the 3a. It had the same cabinet design as the original European AR-3a, and was a relatively short-lived transition model just prior to the introduction of the AR-11 in the mid 1970's. The 3a "Limited" of the early 90's went back to the original US cabinet style. It had an adjustment to the original crossover configuration to accommodate modern 8 ohm L-pad level controls and the AR-11 style (Tonegen) cloth dome tweeter...along with woofer-to-high/mid range jumpers. Most of these have been found to have vinyl clad cabinets, though some have been reported to have walnut veneered cabinets as well. I recall variations in Italy described in this forum some years ago. Although apparently marketed primarily in Asia and Europe, I have seen US-manufactured 3a Limited cabinets. The 3a Limited was an excellent sounding version of the 3a. The Tonegen drivers were of high quality, very consistent, and have held up well. Roy

It appears to me that all of the drivers are Tonegen. This would be consistent with the AR-3a Limited of the early 90's, sold primarily in Europe and Asia. It is unusual, however, to not see level controls. I agree with Gaston, the crossovers should prove interesting. Imo, the drivers alone are worth 400. Roy

20 oz of fiberglass will work fine for the LST and LST-2, and 8 oz for the 6. The earliest version of the 6 contained closer to 11oz. The 3a only used fiberglass. Later AR models with the same woofer utilized smaller amounts (vs fiberglass) of audio grade polyester...which is more dense than that found in a fabric shop. From a sonic perspective fiberglass is the safest choice when restoring old acoustic suspension speakers.

-I would simply replace the existing 12uf cap with your new (3+3) 6uf cap. -Do not remove the surround and spider mounting rings! They provide the proper elevation and dimensions.

The tweeters in your photo are from 3 different eras. The top, lower impedance tweeter is obviously a later replacement from 1976. It would have been used in the 3a or LST (not LST-2). The bottom one is a later (1974) specimen as well. The middle tweeter from 1972 has the red mark ("5') indicating it is a higher impedance tweeter used in the AR-5 and LST-2. Given the situation it is a good idea to replace them all with one type of tweeter. Any capacitor value between 4uf and 6uf should bring your LST-2's within easy tweaking distance of the original sound. You might as well use the capacitors you have available to begin with.

The mechanical properties of the HiVi tweeters are different than the original tweeters. As Ron mentioned above, they have a very different frequency response without the added inductor. Some years ago after a fair amount of experimentation I ended up replacing the original 12uf capacitors with 5uf capacitors. It was for a "Vintage_AR" customer who was happy with the result. Since then Larry has been using that capacitor value for his HiVi/LST-2 kits with no complaints. No measurements were done, but subjectively it fit in very well with the (many) other AR models we had in the shop. Roy

Welcome to the forum, Andre. That is an impressive stack of equipment. The LST-2 tweeters are indeed wired in parallel. If you are using Hi-Vi tweeters you only need 1 inductor per cabinet, wired in parallel across the entire tweeter array. Additionally, the original crossover capacitor value should be reduced for the LST-2. If your tweeters are all original AR tweeters, the preferable approach would be to have them rebuilt. Roy

Thanks for the additional photos (especially of the 755 enclosure) and information, Jeff. Very interesting! Roy

It is a first for me as well, Frank. From Jeff's post above..."The price sheet from AR, dated 12-1-54 stated that “Cabinets with custom dimensions available for models AR-1W and AR-1WU only.” Based on the crude installation of the 755A, it appears to have been a "special" cabinet for the woofer (ie AR-1WU) which was converted to an AR-1 by installing a 755A and an AR-1 crossover. It seems unlikely it would have come out of the factory like that. This speaker was accompanied by other custom equipment suggesting the owner was an enthusiast capable of doing this type of modification. The AR parts would not have been difficult to acquire in those days. I've also never seen that type of crossover wire in an AR speaker before. Roy

Some forum members have had success cleaning the original cloth, but I'm not the best person to ask. I almost always replace it. Your new 2ax cloth looks great.

It is a dual capacitor, 24uf and 72uf, serving the mid and woofer circuits respectively. The brown cylindrical capacitor above the level controls is the 4uf tweeter cap.