Restoration of Acoustic Research AR3 Speakers

[Cropper]

So I fairly recently obtained a pair of AR3 speakers that were in pretty bad shape and, with the generous support of members on this forum and a few other sources (more on that later) I managed to restore them to what I feel is a good representation of their former glory. I wanted to share my process and experience on audiokarma in the hope that it helps someone the way that I myself was helped on here.

First a little background on me - I am relatively young and relatively new to audio equipment collection (last 5 years), although I have loved music my whole life and while I like a lot of music, I am very much drawn to the music of the 50s, 60s, 70s and early 80s (be it jazz, motown, folk, blues, rock or pop). I collect vinyl. So it was probably inevitable that I would one day end up collecting vintage audio gear and I now have Pioneer and Marantz receivers (monster and non-monster), an MC2205, a C29 preamp, an ARC SP-8 preamp, Kappa 8.1s, New Large Advents and DCM Timewindows to name but a few. After a while I decided that collecting wasn't enough and I read these forums and watched videos until I felt confident enough to restore first speakers, and then amplifiers. The Advents were my first project and I can't tell you how I felt when I hooked them up after I worked on them and sound came out - relief and joy doesn't do it justice. I think I yelled 'I made sound!'.

So yes, the AR3s. Like most people on here, I never stop looking for new pieces. Like most people on here there are certain items that you prize above others for various reasons - AR3s were one of those items. Couldn't tell you why. The look, the history, the reviews, the fact they're in a museum, the sound? Just something I knew I needed to try. Plus, and I won't lie, the fact that they sell for crazy amounts and I hoped I now had the skills to restore a pair meant I felt like it was worth the gamble.

One day I was browsing Facebook marketplace when I saw a pair of AR3a speakers for sale that were relatively cheap (not on the side of the road or charity shop cheap, but affordable). Interesting I thought, well I wouldn't mind trying a pair of AR3a, shame they're not AR3. Upon closer inspection however, they were - they were a pair of AR3s that had been factory converted to AR3a in the late 70s using the service that Acoustic Research offered at the time. Using this forum I learnt more about this process, what it meant had happened to the inside of the speakers and decided I would buy them. I secretly hoped I would end up with AR3s but I wasn't worried if they had to stay as AR3a. Here is a pic of them the day I bought them:





These pictures actually don’t do justice to how much work was required. The grilles were broken, cloth stained and ripped, only one woofer worked and wasn't an AR woofer, both tweeters were service replacements and didn't work, both mids were service replacements and only produced low volume. The cabinets weren't awful, but had veneer missing, chips and dents and needed refinishing. In short, I had bought a pair of semi-decent cabinets really. One piece of good news - I still had the original AR3 (not AR3a) serial number and instructions paperwork on the back of the speakers. So I had AR3 speakers technically.

This was the inside:



Again, not ideal. As part of the factory upgrade, these speakers now had an AR3a crossover but no working AR3a components. Crossover had last been touched in the late 70s (although to be fair, it had held up well). All pots were rusted and no longer working. One of the speakers had a mouse skeleton in it...

So with the above in mind, I decided, perhaps crazily, that I was going to embark on a restoration project. The following posts are the steps that I followed (see end for sources used for reference) and what I learnt along the way.

 

[Cropper]

Step 1: Removed grilles, all drivers, crossovers and pots
This step wasn't so bad and made me feel a lot better. The crossover was a little tricky, particularly the coil inductors as they were bolted down. In hindsight I could've just removed the entire board but was worried I would damage the speaker cabinets so I saved the board.

I removed all the fiberglass stuffing, weighed it to make sure it was still the correct amount, and stored in a bag to re-use. These speakers had Kempac paper to protect the woofers but this had predictably deteriorated and I threw way. I bought 28-count crinoline to replace it and installed at the end.

I took out all drivers and as none were worth saving and put them in a box to throw away. I took off the grilles and put to one side:






Step 2a: Sanding the Cabinets
I started on the outside and began by sanding the cabinets. I read up on this forum and opted to use an orbital sander (it looked like it would take a long time by hand), but I was very careful with the sandpaper grade I used (almost finishing sandpaper) and spent very little time near the corners due the risk of losing veneer off the corners (honestly this was where most of the veneer was missing anyway so not much damage I could do!)

This was a quick and rewarding process, made a world of difference. I was able to remove a lot of the scratches and whenever I do this I almost think 'wow might not stain them'. See below for the different stages:







Step 2b: Repairing veneer
As I mentioned, there was unfortunately a fair amount of veneer missing on the corners and (thankfully) mainly at the bottom of the speakers. An example:



Again, after reading this forum I decided to buy veneer pieces from Amazon (try Veneer variety pack by Sauers) that I can use again if needed. Took me a minute but I found one in this pack that was a close match.

From here, it was all about cutting a strip that matched grain and shape as well as I could possibly do. Like any of this, could someone do better, probably, but I felt like I got it to a reasonable state before finishing the wood and it was certainly better than it was. I sanded down the edges and the top to get to the desired size and depth to try and match the rest of the speaker. See below after restoring wood but before finish:



Step 2c: Gluing damaged trim and clamping

So the worst part of these speakers (well I guess most of it wasn't great) was that a piece of trim was starting to come away from (thankfully) the bottom of one speaker. To try and rescue this I decided to re-glue and clamp. After I had finished I would say that while it wasn't perfect, again, it was much less noticeable than it was. An alternative was replacing the whole piece and I didn't really want to do this. I left the woodglue 48h to dry to be safe. Then I followed the 2b process above on veneering. See below for the different stages:







Later I added a little more veneer and sanded away any excess glue. As I say, this is the bottom of the speaker so I was more concerned with it not sticking out forwards than getting the veneer perfect. Once I added more veneer it looked pretty good overall

 

[Cropper]

Step 3: Refinishing the cabinets
To finish the outside of the speakers I opted to first use a wood restorer and then a separate oil finish.
For the restorer I used a rag to apply, left to dry and used steel wool where needed. I actually only did two coats and thought it looked fine as is so stopped:




For the oil, I used a small brush to apply, rubbed it off after a couple of hours, and left it 48h to dry to be safe. I actually only did one coat with this but I know others have done more. They didn't have this shine after I rubbed off the oil of course:



At this point I felt like I had got a pair of speakers! Admittedly they didn't make sound, but you know, baby steps...

Step 4: Building the crossover
So here is where things got really interesting, and relatively unique based on what I have read on these forums. Hold on to your hats here as there is a lot going on:

- Per Classic Speaker Pages ("CSP"), there were 4 different crossovers used for AR3s (labeled A, B, C and D in their schematic guide). Basically they modified it over time 3 times, and then modified for a fourth time when they ran out of the original AR3 mids and had to start using the mids they were using for AR3a instead.
- My AR3 speakers are early AR3s and would have originally most likely been schematic A or B.
- When I got to them, they actually had an AR3a crossover of course. This is a little bit similar to Schematic D for an AR3 but NOT the same.
- There was a chance I could use the coil inductors I had removed but I opted to not even risk this as it was hard to tell if they were the correct values from the AR3a schematic.

So what did I do? Well because I no longer had any working drivers and it is close to impossible to purchase original AR3 mids I did what Acoustic Research did. I bought original AR3 tweeters, then the AR3a mids they used for schematic D and finally managed to find original Alnico Woofers to go with it. So still authentic AR3 per their own design. I did discuss with people on this forum and CSP whether there would be an audible difference compared to an AR3 mid and came to the conclusion that yes, probably it could sound different to a 'Schematic A' AR3 but 1) these speakers are all 50 years old and there are tons of reasons they may not quite sound the same as each other and their original design at this point and b) AR did this exact same design and people bought it so it can't be far off 'the sound'.

Schematic D requires the following components:

- 1 x 30uf capacitor (schematic shows 6 and 24 in parallel but I think this was a convenience thing as AR used to use 24 and 6 capacitors in other AR3 schematics)
- 1 x 6 uf capacitor
- 2 x 0.4mh inductor coil

So once again I had a blank canvas. I decided to buy the following components:

- Jantzen coil inductors from PartsExpress
- Mundorf MCap EVO Oil 3.3uf and Jantzen Silver Z-Cap 2.7uf for the 6uf
- Mundorf MCap EVO Oil 15uf and Jantzen Silver Z-Cap 15uf for the 30uf

I picked the caps based on this wonderful webpage - Humble Homemade Audio. Could I have spent less (or more)? Of course, but these were a set that worked well together per reviews and based on his ratings gave me the highest review rating per $. Yeah I know, I'm boring.

Next, I decided to build the crossover outside the speaker, glue it down, use a european style terminal for convenience and actually mainly was able to crimp rather than solder (a mix of both):



I did a few finishing touches for safety on the soldered pieces, strapped down the coils with cable wire and made use I used the appropriate glue for electronics. Left it overnight to dry to be safe, gave everything a good tug to make sure the soldering was ok, and then dropped it into the speakers. Note how I cut a hole out for the pots - the board would be too thick on top of the original board if I hadn't - again, ideally I would've maybe removed the original board. Because I crimped the wires for the pots it was easy to attach. These are new pots bought from Ebay - I read that I should make sure to buy ones that actually match the old potentiometers and not cheaper L-Pads, unless you wish to modify the crossover. Not tested that theory but went for the safer more expensive option myself.




I used the wiring colors that AR did to make life easier for someone. Also, because the drivers I had were a cross between front wired (original AR3 tweeters) and backwired (original AR3a mid) I had to quickly pop out the terminal on the front of the speaker so I could wire the tweeters. Did this by removing the staples and popping out with a screwdriver carefully, and then resealed it in once I had soldered on to the back of the terminal.




Step 5: Adding the grilles and finishing touches
I actually ended up making two grilles for these speakers. First I bought Saran and attached to the original plastic grilles that I had repaired, but I didn't like them as much as I thought I would. So I purchased 18 Count Lambswool Linen Fabric 18x27 (qty:2) from 123Stitch.com and made my own grilles and these I ended up sticking with. I bought a '3' for each speaker from Kent on the CSP forum and AR emblems from Ebay and glued on rather than using a pin.

I re-sealed the woofer and drivers as instructed by CSP, soldered the tweeter wire (I added more tape than the photo shows below to protect it) and screwed in the tweeter, mid and woofer. I added the grilles I had made with the fabric stapled on.

This is the finished speaker:






Step 6: Listen and enjoy
I have put these speakers together with my Mcintosh MC2205 and C29 preamp and although the speakers are different to any others I have owned. I am often completely blown away by the sound. Hard to describe but I would say it is live sounding, the instruments are incredibly clear and feel like someone is next to you playing. I listened to the Blue Nile - Hats album last night in the dark (don't worry, I'm fine) and it was really something:




Finally, as I said at the start, I could not and would not have even started this project without various entries on this forum and at Classic Speaker Pages. I found these two threads by Glenn (and his comments on mine) on this forum particularly helpful as I know many others have in the past (https://audiokarma.org/forums/index.php?threads/toilet-paper-stop-yields-a-pair-of-ar3s.735482/ and https://audiokarma.org/forums/index...maybe-the-best-end-of-year-score-pics.564520/). On the Classic Speaker pages are both schematics (invaluable for the crossover) and the AR3a restoration guide (invaluable in general).

I hope this has been helpful. I wanted to add one final thing - I have seen it written on here that it may be best not save these AR3s when all drivers need to be replaced due to cost. While I will acknowledge that I would have loved to have been able to get at least some drivers with my purchase I did purchase 2 woofers, 2 mids, 2 tweeters, 4 pots and 2 new crossovers (caps plus coil inductors) for this project. In effect it couldn't have been any worse. I still believe that I can sell these for a profit given the offers I have had and the sales I have seen. So while I didn't do this for money, I do believe even from this pretty dire starting point that it's not a lost cause financially.

I have a lot more photos, please feel free to ask questions, although I am by no means an expert, I will do my best to help and I am sure others will chime in.

 

[HB3]

You did a beautiful job. Something that you should be proud of.

 

[macyjrm]

An excellent report. You have preserved another set of AR3s for you and future generations to enjoy. That in itself is a wonderful accomplishment.

 

[daybreak2350]

Hi, I am new, if this is wrong thread, sorry. Am also restoring two AR-3s (not 3a) so this looks very familiar, nice work! My MIDRANGE and TWEETER drivers need rebuild (prefer to keep originals, not replacements). Two questions:
1) Is any information, articles, photos out there on how to rebuild these at home? I have skills & tools, did "ground-up" rebuild of bad woofer (10-pound magnet one) complete teardown, repair burned-out voice coil/spider/leads, cloth surround, etc. Works great! Otherwise...
2) If not against rules, can anyone advise me on who the companies are that currently restore/rebuild these vintage drivers (not replace)? I am in middle of USA and would prefer shortest shipping distance, presuming the quality of work is equal among different shops.
THANX ~ nice to jump in to this great site and forum!

 

[Corey Hagler]

Hi, I am new, if this is wrong thread, sorry. Am also restoring two AR-3s (not 3a) so this looks very familiar, nice work! My MIDRANGE and TWEETER drivers need rebuild (prefer to keep originals, not replacements). Two questions:
1) Is any information, articles, photos out there on how to rebuild these at home? I have skills & tools, did "ground-up" rebuild of bad woofer (10-pound magnet one) complete teardown, repair burned-out voice coil/spider/leads, cloth surround, etc. Works great! Otherwise...
2) If not against rules, can anyone advise me on who the companies are that currently restore/rebuild these vintage drivers (not replace)? I am in middle of USA and would prefer shortest shipping distance, presuming the quality of work is equal among different shops.
THANX ~ nice to jump in to this great site and forum!

I’m in the same spot as you. Just acquired a pair of decent AR3’s. One woofer is blown and needs replacement. This gentleman has done a fabulous job and I want to keep the drivers original also. Please keep me posted what you find to get these done right and I’ll do the same.

 

[Corey Hagler]

Step 3: Refinishing the cabinets
To finish the outside of the speakers I opted to first use a wood restorer and then a separate oil finish.
For the restorer I used a rag to apply, left to dry and used steel wool where needed. I actually only did two coats and thought it looked fine as is so stopped:

View attachment 1922668


For the oil, I used a small brush to apply, rubbed it off after a couple of hours, and left it 48h to dry to be safe. I actually only did one coat with this but I know others have done more. They didn't have this shine after I rubbed off the oil of course:

View attachment 1922669

At this point I felt like I had got a pair of speakers! Admittedly they didn't make sound, but you know, baby steps...

Step 4: Building the crossover
So here is where things got really interesting, and relatively unique based on what I have read on these forums. Hold on to your hats here as there is a lot going on:

- Per Classic Speaker Pages ("CSP"), there were 4 different crossovers used for AR3s (labeled A, B, C and D in their schematic guide). Basically they modified it over time 3 times, and then modified for a fourth time when they ran out of the original AR3 mids and had to start using the mids they were using for AR3a instead.
- My AR3 speakers are early AR3s and would have originally most likely been schematic A or B.
- When I got to them, they actually had an AR3a crossover of course. This is a little bit similar to Schematic D for an AR3 but NOT the same.
- There was a chance I could use the coil inductors I had removed but I opted to not even risk this as it was hard to tell if they were the correct values from the AR3a schematic.

So what did I do? Well because I no longer had any working drivers and it is close to impossible to purchase original AR3 mids I did what Acoustic Research did. I bought original AR3 tweeters, then the AR3a mids they used for schematic D and finally managed to find original Alnico Woofers to go with it. So still authentic AR3 per their own design. I did discuss with people on this forum and CSP whether there would be an audible difference compared to an AR3 mid and came to the conclusion that yes, probably it could sound different to a 'Schematic A' AR3 but 1) these speakers are all 50 years old and there are tons of reasons they may not quite sound the same as each other and their original design at this point and b) AR did this exact same design and people bought it so it can't be far off 'the sound'.

Schematic D requires the following components:

- 1 x 30uf capacitor (schematic shows 6 and 24 in parallel but I think this was a convenience thing as AR used to use 24 and 6 capacitors in other AR3 schematics)
- 1 x 6 uf capacitor
- 2 x 0.4mh inductor coil

So once again I had a blank canvas. I decided to buy the following components:

- Jantzen coil inductors from PartsExpress
- Mundorf MCap EVO Oil 3.3uf and Jantzen Silver Z-Cap 2.7uf for the 6uf
- Mundorf MCap EVO Oil 15uf and Jantzen Silver Z-Cap 15uf for the 30uf

I picked the caps based on this wonderful webpage - Humble Homemade Audio. Could I have spent less (or more)? Of course, but these were a set that worked well together per reviews and based on his ratings gave me the highest review rating per $. Yeah I know, I'm boring.

Next, I decided to build the crossover outside the speaker, glue it down, use a european style terminal for convenience and actually mainly was able to crimp rather than solder (a mix of both):

View attachment 1922673

I did a few finishing touches for safety on the soldered pieces, strapped down the coils with cable wire and made use I used the appropriate glue for electronics. Left it overnight to dry to be safe, gave everything a good tug to make sure the soldering was ok, and then dropped it into the speakers. Note how I cut a hole out for the pots - the board would be too thick on top of the original board if I hadn't - again, ideally I would've maybe removed the original board. Because I crimped the wires for the pots it was easy to attach. These are new pots bought from Ebay - I read that I should make sure to buy ones that actually match the old potentiometers and not cheaper L-Pads, unless you wish to modify the crossover. Not tested that theory but went for the safer more expensive option myself.

View attachment 1922676


I used the wiring colors that AR did to make life easier for someone. Also, because the drivers I had were a cross between front wired (original AR3 tweeters) and backwired (original AR3a mid) I had to quickly pop out the terminal on the front of the speaker so I could wire the tweeters. Did this by removing the staples and popping out with a screwdriver carefully, and then resealed it in once I had soldered on to the back of the terminal.

View attachment 1922696


Step 5: Adding the grilles and finishing touches
I actually ended up making two grilles for these speakers. First I bought Saran and attached to the original plastic grilles that I had repaired, but I didn't like them as much as I thought I would. So I purchased 18 Count Lambswool Linen Fabric 18x27 (qty:2) from 123Stitch.com and made my own grilles and these I ended up sticking with. I bought a '3' for each speaker from Kent on the CSP forum and AR emblems from Ebay and glued on rather than using a pin.

I re-sealed the woofer and drivers as instructed by CSP, soldered the tweeter wire (I added more tape than the photo shows below to protect it) and screwed in the tweeter, mid and woofer. I added the grilles I had made with the fabric stapled on.

This is the finished speaker:

View attachment 1922682

View attachment 1922687


Step 6: Listen and enjoy
I have put these speakers together with my Mcintosh MC2205 and C29 preamp and although the speakers are different to any others I have owned. I am often completely blown away by the sound. Hard to describe but I would say it is live sounding, the instruments are incredibly clear and feel like someone is next to you playing. I listened to the Blue Nile - Hats album last night in the dark (don't worry, I'm fine) and it was really something:

View attachment 1922688


Finally, as I said at the start, I could not and would not have even started this project without various entries on this forum and at Classic Speaker Pages. I found these two threads by Glenn (and his comments on mine) on this forum particularly helpful as I know many others have in the past (https://audiokarma.org/forums/index.php?threads/toilet-paper-stop-yields-a-pair-of-ar3s.735482/ and https://audiokarma.org/forums/index...maybe-the-best-end-of-year-score-pics.564520/). On the Classic Speaker pages are both schematics (invaluable for the crossover) and the AR3a restoration guide (invaluable in general).

I hope this has been helpful. I wanted to add one final thing - I have seen it written on here that it may be best not save these AR3s when all drivers need to be replaced due to cost. While I will acknowledge that I would have loved to have been able to get at least some drivers with my purchase I did purchase 2 woofers, 2 mids, 2 tweeters, 4 pots and 2 new crossovers (caps plus coil inductors) for this project. In effect it couldn't have been any worse. I still believe that I can sell these for a profit given the offers I have had and the sales I have seen. So while I didn't do this for money, I do believe even from this pretty dire starting point that it's not a lost cause financially.

I have a lot more photos, please feel free to ask questions, although I am by no means an expert, I will do my best to help and I am sure others will chime in.

Amazing job! I’ll be beginning the restore process on my 3’s soon. Can I bug you for direction here and there?

 

[George H]

i am a tinkerer, have had a pair of closely numbered 3's and have fussed over the wires on the mid and tweets repeatedly over the last 20 years, cobbling together strips of copper, capturing the original aluminum leads in folds of copper trace repair strip and crimping them together. Those old Al. leads break when I sneeze, and are not solderable without special flux. Aluminum is lighter and I suppose the reason it was used. So tonight after listening to them I noticed a duller left side and went in again. The tweeter was zip, and the mid came and went when i taped the cone down but wet away when I pulled the tape off. So, I looked at the little dabs of sealer at the 4 points for the old suspension and dug the old stuff out and staying clear as possible of the coils, carefully cleaned the gap and the voice coil of old what looked like varnish and foam sealer and then carefully, always carefully, removed it. Put the cleaned coil back in not forgetting the little pillow under it, and criss crossed more tape to hold it in place flush with the edge of the body. All this without breaking a wire....Then squeezed a dab of Loctite Shoe glue in the little cutouts that serve as the suspensions for these unique drivers. I let it play for a few hours to seat the coil again, and removed the tape. Plays well now and will start on the tweeter which ohmed open. So it will be my next post as soon as I can find something the right size to wind the coil one. I'll switch to copper magnet wire, a little heavier but much more workable soldering wise. The trick is shot if you break a wire on the coil when digging out old sealer, so I picked and pulled carefully with pointy tweezers and a curved dental pick tool that I use for a lot of small work and stayed clear of the coils. and removed the coil. DE soldered the leads to the tweeter knowing that the resolder will be a will be a breeze with the new wire. Got to find a socket the right size and some thin glue to hold the coils together and reglue that dome to the coil, tomorrow maybe.

 

[daybreak2350]

i am a tinkerer, have had a pair of closely numbered 3's and have fussed over the wires on the mid and tweets repeatedly over the last 20 years, cobbling together strips of copper, capturing the original aluminum leads in folds of copper trace repair strip and crimping them together. Those old Al. leads break when I sneeze, and are not solderable without special flux. Aluminum is lighter and I suppose the reason it was used. So tonight after listening to them I noticed a duller left side and went in again. The tweeter was zip, and the mid came and went when i taped the cone down but wet away when I pulled the tape off. So, I looked at the little dabs of sealer at the 4 points for the old suspension and dug the old stuff out and staying clear as possible of the coils, carefully cleaned the gap and the voice coil of old what looked like varnish and foam sealer and then carefully, always carefully, removed it. Put the cleaned coil back in not forgetting the little pillow under it, and criss crossed more tape to hold it in place flush with the edge of the body. All this without breaking a wire....Then squeezed a dab of Loctite Shoe glue in the little cutouts that serve as the suspensions for these unique drivers. I let it play for a few hours to seat the coil again, and removed the tape. Plays well now and will start on the tweeter which ohmed open. So it will be my next post as soon as I can find something the right size to wind the coil one. I'll switch to copper magnet wire, a little heavier but much more workable soldering wise. The trick is shot if you break a wire on the coil when digging out old sealer, so I picked and pulled carefully with pointy tweezers and a curved dental pick tool that I use for a lot of small work and stayed clear of the coils. and removed the coil. DE soldered the leads to the tweeter knowing that the resolder will be a will be a breeze with the new wire. Got to find a socket the right size and some thin glue to hold the coils together and reglue that dome to the coil, tomorrow maybe.

Thank you for these rare details which your fellow tinkerers greatly appreciate! Photos of coil, dome, gap would be nice but more work I understand.

 

[George H]

Thank you for these rare details which your fellow tinkerers greatly appreciate! Photos of coil, dome, gap would be nice but more work I understand.

I will try, you know how things go sideways when tryin something "new"....pics of tools used and cautions applied will follow. My target for the impedance on the wound coil was 2.1 dc ohms, the old coil was at 2.1 with loss or maybe 10 inches of old wire. The number of winds was 11 winds, first layer, and 10 top layers with the old 11 thousandths wire. The DC ohms probably was a little higher before damage and shortening due to numerous repairs in the past. The unwound resistance of the new .008 wire was 2.1 ohms also, but after winding it, the meter read 3.1 ohms ...reactive coupling? The old aluminum coil's resistance measured low. Why? I don't know. I read somewhere the tweets are supposed to be 4 ohms so I am erring on the safe side of too much reactance for the sound, not to be too bright at 3.1 ohm. Thought I had some GC TV-Radio cement coming but the supplier is out of stock, I'm waiting for Monday morning to call and see if they can supply the smaller bottles, it's perfect drying time is ideal for making the wires behave when winding. May try some wood glue or some clear instrument finishing lacquer if the order is a bust. More next week I hope.

 

[George H]

Well, no luck on the cement, Zoro said it would be 90 days? whaat? so I re-ordered from Antique Electronics Supply, and it will be a few days? Had a strange thing happen on the way to another wind up and mic'ing the I.D. of the coil, it's spot on at 1.286! But cannot duplicate the 3.1 ohm from the previous practice coil. It must have been too much flux in the room the other night. The current wind-up mimicked the very first with a 2.1-2.3 ohm reading. I think it is going to be fine as the old coil was 1.7-1.8 ohms depending on the cleaning of the varnish of the leads. I'm having to put more turns on the new coil, the old one was 2 layers, 11 and 10 turns of .0011. With with the smaller wires, I'm turning about 30 turns first layer and 25 on the second on the last layer to get the ohm values right, the depth of the gap will accept another 6 thousandth's I'm hoping so that I can go a little bit wider as viewed on the former I'm using, (a calibrated pill bottle!). Can't go thicker than 1/8" though, (the thickness of the old coil), it would scrape in the gap. Have a strand measuring 2.3 ohms waiting for some cement, I will wind it and bond the cone on with the same cement. Probably should measure the length of that next wire AND find a way to measure the resulting gap between the coil and the magnet once installed...will keep any fellow tinkerers up to date then. This reminds me of some rocket nozzles we were trying make by spinning ablative into a shell with a lathe and a trowel, measure, measure, and then measure again. I think I've fallen into that rabbit hole again.

 

[George H]

Just read the bio on Edgar Villchur, again....an interesting history, he was a curious thinker, and when he found a student who got it in one of his classes , they turned into a great complemental pair, making our music reproduction so fine. Henry Kloss helped to make the whole thing turn from a theoretical concept to a useable device, and Villchur made the drama for making it so desirable to the masses. Can't imagine music reproduction without these guys and the ideas they turned into reality......and if anyone is wondering the pot's are now lpads and the mids were rewound years ago with an acceptable, to me, outcome level wise, using copper magnet wire. Wrote it up here many years ago, but go figure, I was a newby then and again now, I just love entering my login and passwords three times ....more when the cement arrives.

 

[Scott75s1974]

Folks discussed restoring the tweeters in this thread on a pair of Heath AS-2a's (=AR2a)...but didn't share the adhesive formula. Here's a link to Vilchur's patent for the tweeters which has a cross section: #37 It also talks about their construction in some detail.

 

[George H]

Folks discussed restoring the tweeters in this thread on a pair of Heath AS-2a's (=AR2a)...but didn't share the adhesive formula. Here's a link to Vilchur's patent for the tweeters which has a cross section: #37 It also talks about their construction in some detail.

Hey, Scott, your name or quality Marque? Anyway, I am into this repair and got the link you sent to Villchur's patent's, thanks. I am sure the foams used in the suspensions way back then were leading edge, pardon pun, but chemistry and elastomers have come a long way since. I found the Loctite shoe glue( actually a Henkel/Loctite product @ Home Depot) and is a flexible and good adhering substitute for the aerated foam in these old drivers. I am thinking, to make the stuff lighter and more flexible by maybe 25%, I will mix in some Cabosil, just maybe a 50/50 mix by volume, it's a filler we used at work for de-densifying epoxy mixes, for potting electronics and bonding purposes, good old corn starch will work too! I'm agitated at myself I hadn't ordered the TV Radio Cement before this. Good stuff to have handy. It was invaluable at work for laying tiny microphone wiring down in traces where there was no room for anything else. Just waiting on the ground shipping for that flammable elixir, so I can get rolling....

 

[George H]

So a little pre paring for the coil into the gap. I read in the whitepaper on E.V.'s patents, thanks Scott75... that they were cautious about the gap maintenance in the magnet to coil gap. What makes me curious is how did they control this gap? As I was removing the coil, I noticed it was somewhat bound by what felt like a rubbery tension, but not stuck. This was after carefully removing what was left of the foamy suspension divots. I saw there was something akin to a sealer on the outside of the coil. Couldn't figure at first, why they were so sloppy with their glues. But realized there was a method to their sloppiness. Looked as if there was a .010 thick coat of something in three spots on the coil. They probably slid the coils in wet, with this gap control juice and it was their way of controlling the symmetry of the gaps all the way around the magnet. Good way to do this now would be to put thin strips of teflon tape in three spots on the the coils and inserting them carefully not rubbing off the tape into that gap. They "should" stay intact in use. I'm going to try some dry run fits first with some of the practice coils I've already wound..to see what tape thickness' work. The domes will have to wait for final bonding onto the voice coils, I don't want to do too much practicing on those irreplaceable items. And then the surround mix dabbed into the 4 v notches and allowed to cure. I may be wrong in my assumption that they did not want bonding to occur inside the magnet/ coil interface but with the limited excursion/movement in that design, they could live with a minor restriction with this liquid, whatever it was they used. Fun stuff/
Wow Antique Electronics Supply, 2 days from Arizona, awesome, the cement is as as smelly as I remembered it was, but it is a 1 coat and done. 2.3 ohms and ready for test fitting tomorrow, I couldnt't get the coil off the former I'm using for winding....I had to put a few drops of acetone on the leading edge to get it to move...that GC cement sticks to wax paper too. All good tho', going to go easier on the cement on number two.

 

[George H]

my sandbox.

 

[George H]

Me again. I tested the coil in the gap for fit last night, felt smooth going in with a bit more clearance on the outer edge, so will probably use thin strips of .005 Teflon tape, I borrowed from my old employers, to center the coil and dome. Have tried for two hours this morning to frame up the dome to the coil for bonding. Thought I had a decent alignment but when I unweighted it and removed the tape, it had moved a bit, don't think it is a major issue, yet, but the dome will not look centered quite properly. It is sealed though! I could remove it and try again but want so badly to hear this tweeter to see if all this has been worth the effort. I really have to fight my compulsive side sometimes.

 

[George H]

I have success! I give a lot of credit to Scott 75 for the white paper on the original patent by EV. Thanks again. Taped down the cone flush as possible with the frame and will pot the suspensions tomorrow, letting the driver play all night. It was a perceived fail at first, I heard nothing from the driver. Then remembered turning the pot down on the back, and when rotated full open, the magic of Mr. Villchur's invention came right to life. So it's a repeat of the process on number 2. I have missed a lot of things like the dead weighting of the cone and coil bond up, and the make do wire tensioning system, a simple friction of the wire through a piece of upside down sandpaper and taped over the feed in wire. I cut the wire to length before winding, as the spool was quite heavy, and the sandpaper backside had just enough pull on the wire to keep it in place. All things considered, easily done with with a good junk box, and readily available tapes, except for the Teflon tape, which if you check now is probably $200/ roll. I found it handy , but not necessary. It was too slippery for using as a release on the winding former pill bottle, and did not use it. And didn't shim the outer coil as i was contemplating doing, it wasn't needed, and waxed paper worked best as the release on the pill bottle. Just slid the old coil onto the tube to where it stopped on the wax paper and marked it for the build up of tape I used as a fence to hold the winding from moving as turns were applied. That pill bottle was my best find in a tool. Just tapered enough to find the right winding point to match the old coil,. If I remember I'll take pics of the tools used tomorrow and the other stuff too.. thanks for following.
specs:
#32 magnet wire .008 Formvar, former (small pill bottle, available through you local drug store)1.286 (coil ID), coil final OD 1.342/ total turns 35, with first layer of 19 and second layer of 16 plus or minus 2 turns and wire length including flying leads, 135 inches
impedance 2.2 ohms unconnected, parallel value in circuit 14.5 ohms taken at the + and - terminals. Chemicals used were GC TV and Radio cement, acetone, and Loctite shoe glue. Meter: Fluke 112.

 

[George H]

Thank you for these rare details which your fellow tinkerers greatly appreciate! Photos of coil, dome, gap would be nice but more work I understand.

I have been thinking this would be a good project for like minded AR-3 enthusiasts, I hope it was readable. I wandered a little in the discovery phase but it all turned out well. If question's arise let me know. I hope these tweeters and mids can outlive me.