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AR-5 ?


owlsplace

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Back to the 1970 AR-5's that I put aside last year after grabbing them on the auction site initially for spare parts. Prepping the woofers for new foams yielded a little surprise. One of the cones didn't compress when pushed in, oops...

attachicon.gifDSC03729.jpgattachicon.gifDSC03731.jpg

Now you know what a fried voice coil looks like. The other vc shows some discoloration from heat damage. There was enough current flowing to melt the adhesive around the lead in wires and around the dust caps.

Anyway, the challenge: I have a spare vc from a woofer with a bad cone so will see if I can make one out of the two. May need to tap RoyC's brain power on how to line up all the parts :)

Meanwhile back to getting the adhesive off the good vc without damaging anything ... glutton for punishment.

Roger

When you see a voice coil in this condition (from your pictures of the AR-5 woofer), the condition is immediately identifiable: the amplifier self-destructed and passed full-current rail-voltage dc into the voice coil. Huge abuse, "accidental or otherwise," as AR used to say. So therefore, the voice coil was probably briefly set ablaze before the amplifier likely blew its main power-supply fuse during self-destruction. This is all the more reason to protect your speakers against this lethal form of damage caused by poorly designed/protected amplifiers that are unstable or potentially likely to self-destruct. In many instances, the speakers ignite and can cause a house fire in the process.

You would probably be better off trying to find another complete AR-5 woofer rather than attempt to install a new voice coil and spider assembly. The glue used to hold the voice coil in place is a tough, high-temp epoxy-resin material, and it's very difficult to remove without big-time damage to everything around it, but it can be done if someone is skillful and patient.

—Tom

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When you see a voice coil in this condition (from your pictures of the AR-5 woofer), the condition is immediately identifiable: the amplifier self-destructed and passed full-current rail-voltage dc into the voice coil. Huge abuse, "accidental or otherwise," as AR used to say. So therefore, the voice coil was probably briefly set ablaze before the amplifier likely blew its main power-supply fuse during self-destruction. This is all the more reason to protect your speakers against this lethal form of damage caused by poorly designed/protected amplifiers that are unstable or potentially likely to self-destruct. In many instances, the speakers ignite and can cause a house fire in the process.

You would probably be better off trying to find another complete AR-5 woofer rather than attempt to install a new voice coil and spider assembly. The glue used to hold the voice coil in place is a tough, high-temp epoxy-resin material, and it's very difficult to remove without big-time damage to everything around it, but it can be done if someone is skillful and patient.

—Tom

Good synopsis, Tom.

I had to break from this for awhile due to other demands being made on my time. I'm already taking stock of fall projects to determine priorities.

I would still like to take a shot at transferring the voice coil just to see if I can do it. The epoxy comes off slowly with a hot knife. I'll probably have to make a jig to hold everything in place while the epoxy sets.

You are right though, if I had to pay labor it would not be practical :)

Roger

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Crossover caps do block DC flow to mid and tweeter. This may be reason to use something beefier than 50V NPE´s...power rails may exceed 80V DC.

Even then... pulse during big bang can destroy mid or tweeter.

Best Regards

Kimmo

PS capacitor coupled and transformer (not auto transformer) coupled amplifiers as much nicer to speakers when something unexpected happens...

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Crossover caps do block DC flow to mid and tweeter. This may be reason to use something beefier than 50V NPE´s...power rails may exceed 80V DC.

Even then... pulse during big bang can destroy mid or tweeter.

Best Regards

Kimmo

PS capacitor coupled and transformer (not auto transformer) coupled amplifiers as much nicer to speakers when something unexpected happens...

Yup, but I think the 50V caps would hold up long enough for the power supply to blow its primary winding fuse. Then again, that is why I was toying with the idea of copying the original LST blocking caps. Not sure how the sound would change by adding 5000MFD on the common leg. Which brings up another question -- perhaps picking nits but AR was ambivalent about putting the fuse on either the common or plus connections. Seems preferable to put it on the common leg.

Anyway, all my speakers are also fused.

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22000 or 68000 UF capacitor charged at 80V will deliver considerable amount of energy for few seconds in to resistive load after mains fuse has blown. You can use faster blowing fuses in power rails. Amp is also unstable after one phase of output devices have short circuited and the load does have quite often also other than resistive elements... So pulse after big bang can be quite large... fusing or other sort of protection is not too bad idea.

Best Regards

Kimmo

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Sounds like I need to do some testing here using sacrifical drivers :) I think you are correct Kimmo on the need to use 100VDC caps.

Just noticed a pair of 5's on the auction site and the tweeters caught my eye. Seller makes the following statement:

THE TWEETERS HAVE THE ORIGINAL MAGNET DRIVERS, BUT HAVE NEW VOICE COILS INSTALLED. THE ORIGINALS WERE WEAK, AND THE OVERALL BALANCE OF HI END, MIDS, AND LOWS DIDNT BALANCE. NOW EVERYTHING MATCHES BEAUTIFULLY. YOU WILL REALLY NOTICE THE HI END IMPROVEMENT IN THESE SPEAKERS.

Anyone up on this rebuild technique? Here is the listing number: 121686254396

Roger

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Are those AR-5 tweeters?

Looks like a new dome, vc and anti-diffraction/reflection foam. Inquiring minds want to know :)

Can't tell what the suspension is.

post-173498-0-43051900-1435117589_thumb.

Update, seller's response 6/24/15: "hello, same exact size, but not the paper dome construction as original. seller of these says they are silk. and have a 50 watt rating at roughly 8 ohms. they have a very smooth response up to 20khz. ive sold maybe 5 dozen of these to ar owners, and their feedback was all 100% positive. most adjustments these days are done with the amp/receiver tone controls anyways. I think you will be very impressed with these. the balance of hi's to lows, and excellent mids in between compares with the best speakers out there."

Hmmmm, need to find out who is making these tweeters up.

Roger

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  • 2 weeks later...

seen these "replacement" tweeters. I am very interested in what these are and who is selling them. As with all AR owners my tweeters are getting "old" (same with myself).

Would really like to know who this guy is and what he is putting out there. I am bumping this thread so maybe it can get some attention.

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If you make jig that fits in the magnetic gap and extends over front plate of tweeter, you can drill two alignment holes in tweeter front plate. If tweeter cone and VC assembly do have alignment holes in in same positions VC can be aligned using alignment holes. Lot of work, but may pay off if you find suitable recone kit with AR tweeter dimensions. Rebuilt tweeter may be OK, but very unlikely similar to original AR one.

Kimmo

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  • 3 weeks later...
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You may be able to coax more output from your AR-5 tweeters by very carefully scraping away the butyl rubber coating over the voice coil gap.

Roy

I wouldn't recommend removing the gap sealant unless you are ready to replace your tweeters. I tried it yesterday and the butyl rubber was the only thing holding the dome in place. The urethane suspension was totally degraded and I ended up with a detached dome. I dabbed a little Goop on to hold it in place until I decide what direction to take on these old tweeters.

Roger

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I have successfully done this a number of times, but I do not remove the sealant covering the foam suspension.

Otoh, if the foam is that degraded, then it is time to replace the tweeters anyway.

Roy

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I have successfully done this a number of times, but I do not remove the sealant covering the foam suspension.

Otoh, if the foam is that degraded, then it is time to replace the tweeters anyway.

Roy

I think you are right, Roy. That is why I decided to dig in to them.

I guess I'll have to get some HiVi's at this point but I sure would like to hack those old tweeters. The only thing wrong with them is the butyl rubber sealant and the urethane suspension. I am assuming the urethane was used to set the gap and the butyl was used to seal it. Since the butyl is contacting the dome it would also be part of the suspension. Once again I'm assuming it has hardened with age causing a drop off in response.

I'm definitely going to try something with these since I have six of them to play with B)

Looks like it may be next year before I finish the AR-5 triumvirate. I'm working on the unfinished pine cabs at the moment and the remaining original surround is now showing a break so it is time to replace that as well -- past time actually but I wanted to see how long it would go.

Roger

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  • 2 weeks later...

post-173498-0-15262300-1438573967_thumb.

Working on my shellac skills on the Ponderosa Pine boxes. They are still going to look like plywood to me but it will be a nice base for the color coat if I manage to get to it.

I have a built in resistance to using this finish since the first time I did as a child it didn't harden because it was old shellac. It is a nice finish when done well though.

Oh, and they used to tell me when I was growing up if I didn't behave I was going to get a good shellacking :)

Roger

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Looks good to me. If oiled walnut is standard finish, there is room for other finishes too.

It is most depressing to see how some "unnecessary" standards will become very hard to break. Say... 99% all new cars do have same grayish dashboard and trunk lining. Floor carpet of 95% new car is also grayish... It is true that dirt is grayish colored, but why only oriental rugs and wallpaper can use much nicer colors?

Best Regards

Kimmo

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Yeah, Kimmo, these pine boxes were made to be finished by the users anyway which most of them were wherein lies the dilemma since few exist unfinished. I'm still torn whether I should put a color coat on these but they needed something. The unfinished 6's I also have developed craze cracks from drying out. You would have to get up close to see it though. They are getting a good shellacking also. At least one person who has seen them says they like them blonde. I'm not entirely opposed to that. There are plenty of old beat up oiled walnut cabs around if you want to play with colors.

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So as I sat watching the paint dry on this old woofer I wondered how many drivers I would have to refoam before it felt like second-nature -- this one was it, number sixteen from the set that started my personal AR revival was refoamed at Happy Hour today. It lost its virginity at age 43 ;) The only reason it has the JBL foam is because the other woofer of this set does. It will end up partners with two sets of BA foamed AR5's.

Looking at the woofer above my mind wandered back to my original 5's that I bought in Germany while stationed there with the Air Force. I was located on a small site surrounded by farmland. The flight didn't fly in planes. We were forward air control with radar, cryptographic and long range communications capability. I was communications. I believe we were the only unit that had fixed orders if war broke out with the East Block. Not something to brag about -- we were first in and last out types and more likely to get your a$$ blown away :) Anyway, they decided we should run 24/7 so we did shift work. If you were doing swings or mids you had a hard time listening to music during the day with the radar on -- radar only did day shift fortunately because every time the radar swept the barracks it would induce a loud ping into the audio.

Roger

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