Early AR-3a woofer voice coils locked up

RS Steve

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Found a pair of early AR-3a's that have the woofers locked up, I was wondering if anyone has found a way to salvage the cones after this. I know a more modern cone can be put in these, but I'd like to keep the originals. Maybe someone has been able to free them up and save the cones, can't blame a guy for trying. :D
 
Bummer! Someone probably tried to keep using them after the foam surrounds deteriorated and trashed the voice coils. You'd probably be better off looking for some good used ones if that's the case, I'm not sure if the voice coils can be rewound or if the formers can be rebuilt (probably pretty expensive if they can be).
 
Bummer! Someone probably tried to keep using them after the foam surrounds deteriorated and trashed the voice coils. You'd probably be better off looking for some good used ones if that's the case, I'm not sure if the voice coils can be rewound or if the formers can be rebuilt (probably pretty expensive if they can be).

The surrounds are original cloth style, and in good shape. I will pull the woofers out and see what is going on at the spiders. The spider might of come loose and the voice coil popped out of the groove. I hope that's what happened, it might be an easy fix.
 
Are you sure the magnets have not shifted?
DC

Not sure of anything other than they do not move when pushed on, could be they were dropped or something, and the magnet shifted. Seems the most logical, but I will take them out tomorrow to inspect.
 
Bummer. Hope it's repairable. Those woofers, when available, are not cheap.

Glenn
 
I have heard of the spiders coming unglued occasionally on the older cast frame woofers like you have, but I would think there would still be some kind of play (if not a little bit inward then maybe side to side or something) . If they are locked up tight it's not looking too good, and it's kind of weird that it happened on both drivers. Do you know their history at all? It's possible that a failed power amp took them both out (although even that's a little strange since amps usually fail one side at a time). Could have been someone really abusing them and they took a major hit from a bass note, although they would have to be cranked beyond belief using a pretty powerful amplifier.

You can fit truncated 11 3/4" drivers from other speakers in the AR line in there but they probably won't sound exactly the same. Might be close enough though and they aren't too hard to find.
 
Ditto what audiojones said. I've heard the spiders are the bit to keep an eye on with the early woofers. But no movement at all seems odd.

As I understand it, all the classic AR 12" woofers are interchangeable. Not identical, but can be interchanged. But the early ones are so cool with the cast frames and the extra weight added to the cone. Hope they can be fixed.
 
It almost sounds (since it is both and it is the inward movement which seems affected) that someone "overdrove them and forced the the voice coils out of "slot" (or leaks allowed the cone/coil to travel too far).
 
It almost sounds (since it is both and it is the inward movement which seems affected) that someone "overdrove them and forced the the voice coils out of "slot" (or leaks allowed the cone/coil to travel too far).

I would think this would be the best situation, going to grab the speakers now and take the woofers out today. I hope I find a fixable situation. :sigh:
 
One fixed, one to go. :thmbsp:

Wow, I think I can fix anything now. :smoke:

Turns out the magnet had shifted, and pinched the voice coil. Not fully understanding how the magnet assembly was together, I took it completely apart. :nono: It is a very strong magnet to deal with as far as having control of where it sits. But I was able to cut the dust cap off, shim the voice coil, and with a small rubber mallet tap the magnet assembly to center it. I checked the ohms, and it reads 4.3, hooked it to a stereo, and listened to some sweet sound with no rub. :thmbsp:

I'm so happy to have saved at least one, hope I have the same result with the second. :music:
 

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One fixed, one to go. :thmbsp:

Wow, I think I can fix anything now. :smoke:

Turns out the magnet had shifted, and pinched the voice coil. Not fully understanding how the magnet assembly was together, I took it completely apart. :nono: It is a very strong magnet to deal with as far as having control of where it sits. But I was able to cut the dust cap off, shim the voice coil, and with a small rubber mallet tap the magnet assembly to center it. I checked the ohms, and it reads 4.3, hooked it to a stereo, and listened to some sweet sound with no rub. :thmbsp:

I'm so happy to have saved at least one, hope I have the same result with the second. :music:
Having messed with the mids and tweeters I know from experience a good blow can jar them loose. I don't know if they used just the bolts or adhesive and bolts. If both, then you might consider (down the road some) taking them apart, cleaning, and the gluing them back together. Again, I'm assuming that they glued them (as well) like the mids and tweeters. Glad to hear you got them working.
 
Having messed with the mids and tweeters I know from experience a good blow can jar them loose. I don't know if they used just the bolts or adhesive and bolts. If both, then you might consider (down the road some) taking them apart, cleaning, and the gluing them back together. Again, I'm assuming that they glued them (as well) like the mids and tweeters. Glad to hear you got them working.

Now the second woofer is fixed also, woooohoooo! I can't help but be super relieved. Maybe even dancing bannana happy! :banana:

I used the bolts to loosen it all up, put some glue in between everything, snugged them slightly, then tapped on the outer magnet plate until I had an even slot for the voice coil. I then used shims to make sure the gap was equal, then tightened the magnet assembly. Next I reglued the original dust cap back on. I have the first one playing while the dust cap dries on the second.

These are pretty original except for the finish, someone faux finished a dark, very dark mahogany finish on them. The capacitors are still original, and the panty hose like socks for the woofers are still inside. They came with new grills and badges. :thmbsp: The one sounds pretty good, and the pots have no dead spots in them, which is amazing. Can't wait to get them both going and get an idea of how they were in their day, even though the caps are probably way off their specs.

Only one of these still has a tag attached, I'd say they are very early 3a's with a serial # of 71. :yes:
 

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Glad you got them up and running.....reminds of a story about them. I rebuilt a set about two tears back. EWverything went great on the rebuild, new finish, cleaned pots, re-cxap, etc, etc. Went to play them and they sounded very weak- almost no bass, mids. twtr fine. Long test story short, the original Alnico magnets had lost their charge!!!! Drove me real crazy figuring that one out!!!
DC
 
The magnet structure, all of it, needs to be very tightly coupled. Small magnetic gaps will increase the reluctance and thus reduce the magnetic field in the VC gap. With that in mind, I don't see how the magnetic structure can be jarred loose unless the construction was initially at fault. Bolts, not glue alone, needs to be used to keep the magnet in extremely close contact with the gap structure.

Further, the actual geometry of the magnet-gap structure should be optimized/designed to avoid magnetic saturation of any part of the structure which also reduces the efficiency of the whole structure. I've seen studies of such designed using Finite Element Method, which is possible with computer-aided design applications. Hard to believe that older speakers were designed with optimized magnetic structures. But some of them were/are durned good speakers in spite of that.
 
The magnet structure, all of it, needs to be very tightly coupled. Small magnetic gaps will increase the reluctance and thus reduce the magnetic field in the VC gap. With that in mind, I don't see how the magnetic structure can be jarred loose unless the construction was initially at fault. Bolts, not glue alone, needs to be used to keep the magnet in extremely close contact with the gap structure.

Further, the actual geometry of the magnet-gap structure should be optimized/designed to avoid magnetic saturation of any part of the structure which also reduces the efficiency of the whole structure. I've seen studies of such designed using Finite Element Method, which is possible with computer-aided design applications. Hard to believe that older speakers were designed with optimized magnetic structures. But some of them were/are durned good speakers in spite of that.

I did my best to get them lined up, and everything tight. They both sound very good for having ancient capacitors still in them. The bass is AR awesome, woofers seem to be working great.
 
Glad you got them up and running.....reminds of a story about them. I rebuilt a set about two tears back. EWverything went great on the rebuild, new finish, cleaned pots, re-cxap, etc, etc. Went to play them and they sounded very weak- almost no bass, mids. twtr fine. Long test story short, the original Alnico magnets had lost their charge!!!! Drove me real crazy figuring that one out!!!
DC

These magnets were so strong that one ripped my finger nail half way off when I was trying to slowly put it together. Ouch!
 
These magnets were so strong that one ripped my finger nail half way off when I was trying to slowly put it together. Ouch!

That sucks, but great you got them working.
These are the better woofers used in the 3a's. Great bass, better than the later foam surround, ceramic magnet woofer.

The bass from my 3's is just amazing, glad you're experiencing it too!
 
That sucks, but great you got them working.
These are the better woofers used in the 3a's. Great bass, better than the later foam surround, ceramic magnet woofer.

The bass from my 3's is just amazing, glad you're experiencing it too!

I should of taken pictures of the voice coils, man are they beefy. I wonder how many of these woofers were tossed with the problem mine had. :scratch2:

I really can't understand how they got like that, unless someone messed with them. If someone loosened the middle bolt, the magnet pole can move inside the structure.

All I know is they are playing great, even my wife likes their sound.
 
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