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Old 22nd Aug 2019, 11:51 pm   #1
DonaldStott
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Default Acoustic Research AR28s

Not really Vintage but from the 1970s I'm now onto restoring a second pair of Acoustic Research AR28s loudspeakers.

This will involve the usual re-foaming of the main drivers and replacement of the large capacitor on the crossovers. Cabinets are in good physical condition, just need a clean and polish, while the speaker grill cloth is ok as well.

There is one small problem though and that is that at some point the speakers have been over-driven resulting in both tweeters being blown - a common occurrence! I have disassembled the tweeters and can see where the damage is - in both instances it's the section of wire that runs from the tweeter coil to the connection terminal. Only about a half inch gap where the wire has obviously been frazzled!

Suggestions please on how to bridge that gap and what sort of wire to use?
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Old 23rd Aug 2019, 5:35 am   #2
BulgingCap
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Default Re: Acoustic Research AR28s

I did a similar repair on a replacement tweeter for one of my Allison speakers. I reasoned that as the movement of the dome, or 'nipple' in this case, was so small as to be not measurable I could use thin lacquered copper. It has performed perfectly for years. Of course a bigger driver would need the braided type pigtail because of the large excursions.
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Old 23rd Aug 2019, 7:16 am   #3
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Default Re: Acoustic Research AR28s

I've pulled a turn or half tun off the coil before or just use any bit of thin wire, the wire is a royal pain in the bum to handle but it can be done, best done in the morning when your fresh and full of T/coffee.

Andy.
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Old 23rd Aug 2019, 9:19 am   #4
DonaldStott
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Default Re: Acoustic Research AR28s

Thanks to BC and Andy for your quick responses.

What gauge of wire would be appropriate - most lacquered copper wire I can find is about 36-38 AWG?
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Old 23rd Aug 2019, 10:56 am   #5
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Default Re: Acoustic Research AR28s

On closer inspection the damage seems more extensive than I first thought!

The braided wire that runs around the base of the tweeter coil is disconnected at both ends - see attached grainy picture: -

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Not sure what this type of braided wire is called or if it can be replaced?

This "repair" may be a step too far ...?
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Last edited by DonaldStott; 23rd Aug 2019 at 10:56 am. Reason: Typo
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Old 23rd Aug 2019, 1:19 pm   #6
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Default Re: Acoustic Research AR28s

It's not clear what you are referring with 'braided wire'. Maybe some more pictures of the whole unit and close-ups. I have a pair of AR speakers but not sure of the model number as there is no ID on them. Your picture shows the exposed edge of the voice coil, which will be a single layer wind of thin lacquered copper wire. The black dished material around the copper coil and bonded to the face of the tweeter is the actual flexible support for the voice coil. I suspect that there should be a dome over the end of the voice coil. This transfers the movement of the coil into movement of the air to produce sound. I cannot easily get to my tweeters as 4 sides of my ARs are covered with speaker cloth and it is a ****** to remove to see the drivers. I have several dead and dismantled tweeters that I can photograph for comparison if you like. I take it that the lead-out wire that has broken exits from the rear to the tag connector, not across the front as in the Allison type?
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Old 23rd Aug 2019, 1:22 pm   #7
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Default Re: Acoustic Research AR28s

I have just realised- is the picture of the back of the coil with the magnet removed? I can see a plastic dome down inside the coil where I would expect to see a pole of the magnet if looking from the front. Sorry for the confusion- more pics needed.
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Old 24th Aug 2019, 7:24 am   #8
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Default Re: Acoustic Research AR28s

Some better pics would help but from what I can see and if it were mine I'd strip some copper wire, get three or six strands and plait it, and use that, however any bit of thin flexible wire as long as it fits will do the job as would de-soldering braid probably.

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