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An interesting variant of the AR-3


JeffS
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Found this pair of AR-3's stored on a basement shelf at an estate sale earlier today. There were no grills and no labels on the rear and, hence, no serial #'s. At first I thought they may have been user modified, having a 3a woofer and midrange, so I pulled the woofer on one speaker to find matching dates on the woofer and tweeter, and a dual cap with 6 and 2 microfarads in the mid and tweeter circuits. Very interesting. I've never seen the 3a woofer in an AR-3.

AR-3 pair 4-27-17.jpg

AR3 front.jpg

AR3 rear.jpg

AR3 tweeter.jpg

AR3 woofer.jpg

AR3 xover.jpg

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18 hours ago, GD70 said:

Interesting. I'm sure Roy will have some enlightening info.

Not sure, guys...I have not worked on many post 1970 AR-3's, and these appear to be just that.

The drivers' date stamps suggest they are late AR-3's, which were equipped with the later ferrite magnet/ foam surround woofer and the 3a type of mid. Other than an additional .4mh coil across the mid, which appears to be present,  the crossover should be much like earlier versions (check out the drawings showing various iterations of the AR-3 crossover in the CSP Library).

These specimens actually look very original to me, with no obvious signs of non-AR tampering. I would love to get a closer look at the capacitor connections and the values printed on the larger cap. I'm wondering if only the 6uf leg of the smaller dual cap is connected. If not, I have no idea what the role of the 2uf leg is.

If these are all original, and I believe they are, it suggests the alnico woofer was no longer being used in the AR-3 in June of 1971. Tom should be along any minute.

Roy

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6 hours ago, RoyC said:

I would love to get a closer look at the capacitor connections and the values printed on the larger cap. I'm wondering if only the 6uf leg of the smaller dual cap is connected. If not, I have no idea what the role of the 2uf leg is (yet).

I'll try to provide more crossover detail this weekend.

I did get a few minutes to check the drivers and they all work, however the pots don't. That made me happy as there were a lot of low to medium power receivers (70's to early 80's) at the sale that could have blown these tweeters.

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Re: caps, I suspect that Roy's thoughts are touching on both curiosities. It appears that the 2uF portion remains unused but was not blacked out, which was typically done (see pic attached) when a cap section was abandoned. Also, it looks like the large cap is quite possibly a dual 6uF/24uf cap, as shown in late AR-3 schematic. 

(Also, almost forgot to to say  "great find", and I love that pic of the basement.)

AR-3 x-o late.jpg

ICC cap.jpg

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This is a great find, indeed! It is my first glimpse at the innards of the last iteration of the AR-3. With confirmation that only the 6uf leg of the dual cap was used, my last question would be what the inductor values are. The "end of production" AR-3 schematic from the CSP Library posted by ra.ra shows them to be the same (.4mh), but it appears this may not be the case.

It also dovetails with a recent discussion I've been having with Tom T. regarding the extent to which the alnico woofer was in use after 1970. The ferrite magnet woofers in the photos above have the same 1971 date as the other drivers, and are consistent with the "long" voice coil leads found in 1971 era woofers installed in AR-3a's of that era. I have little doubt these are original to the cabinets. I wish we had the cabinet serial numbers.

The nice thing about this iteration of the AR-3 is that it does not have the original style midrange(s) with the increasingly common "petrified dome suspension" issue.

Roy

 

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I am not familiar with the intricate details of the AR 3-series iterations the way so many of you are, but the most surprising thing to me is to know that there was a late version AR-3 being factory supplied with a foam-ferrite woofer - - - total news to me! We all know about the early model 3a's that were assembled with the cloth-alnico woofer, but I don't think I've ever seen this permutation presented or discussed.   

Good question from Roy about the coils - - - they appear to be marked "2" and "3", but it almost looks like they have a similar amount of wound wire under the spool. :blink:

Presuming that it is a dual cap under the coils, I would assume that a modern re-cap would result in a slightly simpler wiring scenario, with just a single (or multiple to total) 30uF cap for the midrange driver. Geez, are there six wires attached to that mid pot? But.... if this AR-3 speaker is using LF and MF drivers from the 3a, it is a bit curious that this value is not the more typical 50uF found in the 3a. :wacko:   

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8 hours ago, ra.ra said:

Presuming that it is a dual cap under the coils, I would assume that a modern re-cap would result in a slightly simpler wiring scenario, with just a single (or multiple to total) 30uF cap for the midrange driver. Geez, are there six wires attached to that mid pot? But.... if this AR-3 speaker is using LF and MF drivers from the 3a, it is a bit curious that this value is not the more typical 50uF found in the 3a. :wacko:   

ra.ra,

The AR-3 crossover is much simpler than the 3a crossover, and the 6uf tweeter cap is the only capacitor common to every iteration of the AR-3 and AR-3a.

I'm pretty sure the dual cap under the coils is the usual 24uf/6uf AR-3 capacitor, wired in parallel to make the 30uf cap for later mids. The 3's dual midrange cap was originally used as a 24uf cap for the mid and 6uf cap for the tweeter. When the change to 30uf was required it was simply wired in parallel, and a second 6uf cap was added for the tweeter. (I've seen AR-LST crossovers using a combination of 20uf Sprague caps and older 10uf Industrial Condenser wax block caps to make its 30uf midrange crossover cap.)

The original AR-3 crossover places only a .4mh coil in series, and no parallel capacitor with the woofer, vs the 3a's 1.88mh or 2.85mh series coils, and large 150uf parallel capacitor, so the AR-3's electrical crossover was much more gradual for the well behaved alnico magnet/cloth surround woofer. The ferrite magnet/foam surround woofer is not as smooth at higher frequencies, which is the reason for the 3a's change to the larger (2.85mh) coil when it began using this woofer. I'm curious if we will find a larger coil value in this pair to provide a steeper cut off for the later woofer.

Roy

 

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Interesting stuff (well, maybe only to AR geeks like us). Going off on a slight tangent, here's a question for you, Roy. You wrote 

7 hours ago, RoyC said:

the AR-3's electrical crossover was much more gradual for the well behaved alnico magnet/cloth surround woofer. The ferrite magnet/foam surround woofer is not as smooth at higher frequencies, which is the reason for the 3a's change to the larger (2.85mh) coil when it began using this woofer.

You're familiar with my ar-3/3a conversion but to briefly recap: They were 3s but I could only salvage the cabinets and cloth-surround woofers. You provided some very nice AR-11 mids and I used the Hi-Vi tweets. The crossover was pretty much built from scratch as a late AR-3a xo. The only mod IIRC was the addition of a series cap to the tweeter.  I'm using the #9, 2.85mH woofer inductor. Should I swap that out for something smaller?

-Kent

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10 hours ago, RoyC said:

I'm pretty sure the dual cap under the coils is the usual 24uf/6uf AR-3 capacitor, wired in parallel to make the 30uf cap for later mids. The 3's dual midrange cap was originally used as a 24uf cap for the mid and 6uf cap for the tweeter. When the change to 30uf was required it was simply wired in parallel, and a second 6uf cap was added for the tweeter.

Roy, I agree that the hidden cap under the coils is most likely the dual 6uF/24uF, and I also agree that the wiring scenario you suggest (combining in parallel the 6 and 24 of the dual cap to make 30 for the mid) would be a more sensible arrangement, as shown in the proposed schematic shown here that I cobbled together for this post.

However, that is not how the crossover shown by JeffS has been wired - - in fact, it appears to have been wired exactly like the schematic I showed in a previous post. If you look closely in the x-o pic, from the dual cap you see the green (24) wire attach to the mid pot, while the black (6) wire goes to the tweeter pot. These two caps have not been combined in parallel. Regardless of which wiring scheme was implemented, the results would be the same for the speaker performance, but it's kind of silly to take the normal dual cap, split off the 6uF for the tweeter, and then add another 6uF cap to boost the mid value to create 30uF. As you have suggested and I have sketched (below), it makes far more sense to simply have one wax block cap per driver.

Although the wiring is a bit cumbersome IMO, it is easy to understand why it might have been done this way, and that is because the two crossover components (6uF cap and 0.4mh coil) required to accommodate the AR-3a mid were simply viewed as mere additive items to the previous AR-3 (version C) crossover that the assembly line was already used to cranking out.     

And to correct my earlier statement, I think there are actually seven wires connected to the mid pot tabs: (2) green to #1 tab; (2) yellow and (1) coil to #2 tab; and (1) green and (1) coil to 'B' tab, as seen in crossover photo supplied by the OP.

 

AR-3 x-o late. (v2)jpg.jpg

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Hi Kent,

In my opinion, the smoother response of the alnico woofer makes it more flexible, so it works at least as well as the later woofer when used with the larger coil. If they were mine I wouldn't swap it out for the smaller one. An advantage of the larger coil is the ability to use either woofer.

Roy

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I reopened the cabinet this morning to get more detail on the crossover.

lakecat and Robert are correct that there are 2 wires coming out of the small cap block and that the unused value was not blackened out. The other cap is a dual 24 / 6 microfarad unit. So, as Roy and Robert guessed, this crossover looks like the AR-3 crossover schematic posted yesterday with the small block cap wired in parallel to the 24 microfarad section of the dual cap, giving 30 microfarads for the mid. The coils appear to be the same. I plan on taking them to work with me on Monday to measure them with an LCZ meter. Referencing the 'Rebuilding the AR-3a' document, the woofer appears to be the A.2 and the midrange the A.12. The tweeter looks and sounds like its in good shape with only some surface rust on the plate.

Geoff, I wish I knew the history of these. My guess is that they were ordered directly from AR in 1971. The first picture in my original post is the picture the estate sale company posted one day previous to the sale. From the shape of the cabinets I would guess they had sat in the basement for some time. One of the employees of the estate sale company said that they had filled a dumpster with stuff, including speakers, and hauled it away previous to the sale. Luckily AR-3's are heavy and they probably didn't want to carry them out of the basement. Better to let me pay $25 for the privilege!

Glenn, I threw in some cabinet pictures. What's the best way of dealing with the split edge seams?

xover.jpg

coils.jpg

tweeter.jpg

front.jpg

rear.jpg

seam1.jpg

seam2.jpg

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2 hours ago, ra.ra said:

Roy, I agree that the hidden cap under the coils is most likely the dual 6uF/24uF, and I also agree that the wiring scenario you suggest (combining in parallel the 6 and 24 of the dual cap to make 30 for the mid) would be a more sensible arrangement, as shown in the proposed schematic shown here that I cobbled together for this post.

However, that is not how the crossover shown by JeffS has been wired - - in fact, it appears to have been wired exactly like the schematic I showed in a previous post. If you look closely in the x-o pic, from the dual cap you see the green (24) wire attach to the mid pot, while the black (6) wire goes to the tweeter pot. These two caps have not been combined in parallel. Regardless of which wiring scheme was implemented, the results would be the same for the speaker performance, but it's kind of silly to take the normal dual cap, split off the 6uF for the tweeter, and then add another 6uF cap to boost the mid value to create 30uF. As you have suggested and I have sketched (below), it makes far more sense to simply have one wax block cap per driver.

Although the wiring is a bit cumbersome IMO, it is easy to understand why it might have been done this way, and that is because the two crossover components (6uF cap and 0.4mh coil) required to accommodate the AR-3a mid were simply viewed as mere additive items to the previous AR-3 (version C) crossover that the assembly line was already used to cranking out.   

I see your point, ra.ra, and agree. AR simply added another 6uf cap in parallel with the original 24uf side of the dual cap to make 30uf...same outcome. As you suggested, it was probably easier to add the 6uf cap to the original crossover scheme in this way, rather than change the original wiring. In the past few years I haven't been noticing the details... just removing and replacing the dual cap, and associated nest of wiring, with a new single (era dependent) 24uf or 30uf cap, and 6uf cap (along with the pots). In spite of the original dual caps, and the discussion above, the 3 is really an easy model to re-cap.

Of course to make it more interesting, Jeff's specimens are the first AR-3's I've seen using one half of a dual 6uf/2uf cap. AR must have been clearing out the parts bin to slap these later 3's together. I believe AR was offering the AR-3 to AR-3a "upgrade" about this time, so the 3's days were numbered.

 Jeff, I'm looking forward to learning the inductor values!

Roy

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Quote

 

The number 2 looks to have more windings than the 3 to me. As far as the corner splits, I would brush or pour good wood glue into seam and bar clamp as tight as possible. Let dry and if still a seam....then fill with walnut epoxy from Mohawk and sand to smooth when dry.

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Bondo is not an adhesive. It is used to repair damage as much as car bondo is used...and you wouldn't use car bondo to stick metal pieces together either...:) You cannot compress dry particle board with much success either. It needs to be saturated with WOOD glue to soften it....then clamped. It may not do much but it will strengthen the miter.

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Fortunately, that seam doesn't look too bad (unfortunately it's on top). I agree with the cat--wood glue, heavy clamps, epoxy. I'd just add a couple of thoughts:

  1. Elmer's wood glue comes in a walnut color
  2. if I were doing it. I'd mix Mixol #22 (tobacco) stain with liquid 2-part epoxy, force it into the open seam, cover with wax paper and clamp as tightly as possible.

I did this with a very badly damaged EMI speaker and the results were just OK but with yours you may be able to get pretty much perfect results

-Kent

07 17 16_0635.JPG

07 17 16_0640.JPG

07 21 16_0733.JPG

07 21 16_0734.JPG

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Compressing particle board dry will crush the loose, "crunchy" bits that will never have any structural strength and enable you to remove them with some compressed air. It's basically the equivalent of gouging out all the soft, rotten wood in a windowsill before you reconstruct it. Then you flow resin into the openings and compress them wet.

Regular wood glue is good for sticking wood together, but it won't add strength to particle board that's been weakened by water.

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The split joints  are repairable. You'll need to be brave as surgery is required!

Youll need to dig out and remove the softened partial board as much as possible. The idea is to give the space needed to clamp and pull the corners back together. Do some testing with the clamps to see if the edges come together without any gaps. If not, remove more particle board. Once they pull together, remove the clamps, saturate the joints with epoxy. I use ZPoxy. It's very thin and the particle board will absorb it. It can help to warm up the area with a hair drier prior to adding the epoxy into the gap. Often the particle board absorbs the epoxy like a sponge at first, so make sure you have a decent amount mixed and continue to add it to the gaps. I usually wait 15 minutes or so before clamping. Less epoxy will squeeze out. You don't want a lot of excess epoxy squeezing out, and you should keep paper towels handy to wipe it away immediately as well as acetone.

The epoxy will make the particle board far stronger than it was original.

Glenn

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On 4/29/2017 at 2:33 PM, RoyC said:

Jeff, I'm looking forward to learning the inductor values!

Roy

I finally got around to measuring the coils.

Using an HP 4276A LCZ meter set at 120Hz, the values were 0.412 and 0.407mH. At 1kHz the values were 0.396 and 0.391mH. This meter was last calibrated in 2012. As a second check, I measured using a handheld Tenma 72-8155. Values were 0.422 and 0.417mH at 1kHz.

So, the coils are essentially the same value and the crossover is exactly as stated in the 'Thoughts on AR-3 Schematics' for serial numbers above C70228.

What else was AR using the 6/2µF block cap for (possibly running in series to get 4µF for the AR-5 tweeter)?

 

 

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3 hours ago, JeffS said:

I finally got around to measuring the coils.

Using an HP 4276A LCZ meter set at 120Hz, the values were 0.412 and 0.407mH. At 1kHz the values were 0.396 and 0.391mH. This meter was last calibrated in 2012. As a second check, I measured using a handheld Tenma 72-8155. Values were 0.422 and 0.417mH at 1kHz.

So, the coils are essentially the same value and the crossover is exactly as stated in the 'Thoughts on AR-3 Schematics' for serial numbers above C70228.

What else was AR using the 6/2µF block cap for (possibly running in series to get 4µF for the AR-5 tweeter)?

 

 

Thanks for the information, Jeff!

I don't recall seeing a 6/2 dual cap In an AR cabinet until now. Maybe Industrial Condenser gave AR a good deal on old stock. :)

Roy

 

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