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AR9LS 3/4" Tweeter restoration


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Sorry for my bad English i am from Denmark.

I have restored my old AR9LS from 1983. Rebuilding the crossover to AR9LSi with new capacitors and re foaming the 10" 12" 8" speakers.

Now I've discovered that the 3/4" tweeter are blown in both speakers and no one on E bay for sale.

I bought some 0,12 mm. copper wire and i will try to make a new coil at 4 ohm.

Has anyone tried it?. Or someone who knows if you can take a coil and dome from another AR 3/4" tweeter that fits in the original?.

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I'm on my tablet, and I can't 100% verify this comment, as my tablet can't open the .Tif files.  But, double check the Library, in the AR Drawings section, for exact part tweeter numbers, as that looks like the standard 0.75" tweeter diaphragm.  It's used across many AR speakers, including AR9s, AR90s, AR91s, AR92s, AR38Bs, AR48Bs, AR58Bs, and AR1MS speakers.  The mid-tweeter plate, as used on the 38s, 48s, and 58s can be found fairly cheap, and those tweeters could be used for donor diaphragms, on your 9LS speakers.    

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On 6/4/2019 at 11:50 AM, BjarneAndersen said:

...if you can take a coil and dome from another AR 3/4" tweeter that fits in the original?

The Library section on this website offers some very good information regarding your dual dome driver - - I believe this is part no. 200048 that employs the singular shared magnet structure. A low-resolution copy of the drawing for this driver(s) is attached which includes detailed assembly notes, but there is also a separate document regarding performance specs not shown here. A few portion of blow-ups are shown FYI, too.

I think Stimpy makes a good suggestion here, but there are other drivers that might also be suitable parts donors. A quick look suggest that the tweeters from the AR-58s or the AR-9/90/91/92 series have similar construction - - the outer dome and underlying wood button are identical parts numbers ,but the voice coil/surround part number might be different. I suppose this might difference have an affect on performance, but it appears these parts should "fit".  

048 dual dome.jpg

048 dual front rear.jpg

048 dual section parts.jpg

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  • 3 weeks later...

@BjarneAndersen

Hello Bjarne, 

Unfortunately the coil is out of focus. It seems that you made only one layer winding covering all the former. If so, this is not correct. 1) the winding must be a two layer winding and 2) the former must not be covered completely.

In the AR Library  I've found the tweeter voice coil drawing   of the "Lamba driver" used in the AR 9 LS, 98 LS and 78 LS. It is the 241th drawing.

As regards wire, even though the drawing reports: "2 wire: 22 to 24 turns of N° 38 AWG (a diameter of about 0.1 mm) copper……….. in two layers, 11 to 12 turns per layer", actually I have usually found an inner layer of 14 turns and an outer layer of 11 turns.

Hope you removed the tweeter diaphragm only mechanically since  solvents usually  change tweeter suspension stiffness permanentely and consequentely the tweeter FS and Thiele-Small parameters. 

Luigi

 

 

 

 

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  • 2 weeks later...

I managed to make 2 new coils in two layers, first layer in 12½ turns and second layer in 11 turns.

But there is something strange for, according to the original drawing, the coil should be between 3 to 3.7 ohms.
I measured the old wire with a micrometer screw to 0.12 mm and a length of 1.65 meters and measured it to 4 ohms.

The new coil is also made of 0.12 mm. wire 1.65 meters long and measures 4 ohms.

I don't know if they just had a bad day at the factory when they made it. But I am currently satisfied with the result.

 

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