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AR-5s heading for a rebuild


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For the first time ever since I have been watching the auction site for ARs a pair of 5s turns up - in mahogany

 

AR5s full front.JPG

 

AR5s profile.JPG

 a bit bumped around here and there, but nothing tragic, Grilles a bit grubby, but pretty intact. Nicely consecutive numbers.....

AR5 paper 22018.jpgAR5 paper 22039.jpg

 

....the first time I have bought any ARs in the UK without speckled backs...

 

AR5 timber backs.JPG

 

Alnico woofers with flat caps.....

 

...

AR5s fronts off.jpg

....both cones of which move freely. Boston FFs on order. I noted as per previous threads.....

 

AR5 under woofer.jpg

 

......fibreglass between Kimpac and woofer. First time I've seen that.

 

Woofers have very, very faint dates, in red, on the actual metal....AR5 woofer close.JPG

 

which seems to be Sep 23 1971. Crossover is all wax caps, and the later coils #10 and #11;

 

AR5 crossover.jpg

 

....with an immense amount of degraded rubber foam (the other one is worse). MEK is the only thing that seems to shift that stuff...

 

Pots range from the usable to the wretched

 

AR5 good control.jpgAR5 bad control.jpgAR5 control silver gone.jpg

 

and includes a melter...

 

AR5 control melt.jpg

 

I think I will have two good ones for the mid units, and will just put a jumper across the bad ones to max out the tweeters. I can't imagine they will be too bright.

 

One 4uf cap seems to have survived quite well

 

AR5 ESR yellow.jpg

 

and one not so much....but still not too bad...

AR5 ESR red.jpg

 

But I'll be replacing those I think. I will test the double tomorrow; I'd be interested to know what anyone thinks the ESR should be, either on the double or the 4uf. If I change the double, which I expect to have to do, I will be preserving the old case, I hope, as per Roger's AR-5 resto of a few years back, and stuffing it full of paralleled caps. (Although the writing on his was very nicely preserved, whereas mine is wrecked by gloop.)

Both tweeters measure 5.6 ohms, so I'm hoping they're OK. 

Chuffed to bits with these; but working in a 10" hole is a bit of a test.....I thought the AR-3a was tough....

Tim

 

 

 

 

 

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MEK is really nasty stuff. I think I used odorless mineral spirits.

Nice unmolested pair of Loverly's ;)

I can measure some old caps if you are really interested. The esr will vary and so will dielectric loss on these old caps.

You can probably get a date off one of the other drivers by putting a mirror and torch inside the cabinet.

My AR-5 project got waylayed this year but you may inspire me to hook one up and take a listen again.

The only sequentially numbered 5's I've seen to date were Unfinished Pine and yours are close but no exception.

I have seen pots with internal jumpers soldered in at the factory white dot setting or slightly advanced rather than bypassed. You could do that with the fried midrange pots and put the good ones back into the tweeter circuit.

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Lakecat; you are right in that the finish seems much harder than the other finishes I have on other models. I wonder why the mahogany got a layer of varnish/laquer (?) when the teak, walnut etc seems not to have.

Roger, if I am to replace the existing caps with film I would need to know what value series resistance I would need to put in place  , and I can't seem to find this info in previous threads. Anything you have on this would be very welcome. 

Your comment on the internal jumpers is very interesting. If you or anyone else has any photos of this I would be glad to see them.

regards/Tim

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1 hour ago, TimmyTonga said:

... Roger, if I am to replace the existing caps with film I would need to know what value series resistance I would need to put in place  , and I can't seem to find this info in previous threads. Anything you have on this would be very welcome. 

Your comment on the internal jumpers is very interesting. If you or anyone else has any photos of this I would be glad to see them.

I think consensus on series resistance would be that it reduces output in these drivers that are already suffering from age-related output loss due to stiffening of their suspensions.

Personally I would just replace the pots but the one I remember seeing had a wire soldered from the center rivet to the resistance wire. You can also just substitute fixed resistors in place of the pots. The later AR speakers utilized this technique with switchable resistance values. Not sure AR made any crossovers that actually used L-pads.

Roger

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