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Incoming AR-7's


owlsplace

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Well, since I liked the 6's so much I couldn't resist these consecutively numbered AR-7's that were languishing down in AZ on the auction site about to close without any bids.

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Funny part is I have a friend who lived in that area for 15-years and just happens to be there currently for a few weeks. She graciously agreed to pick them up and bring them back for me so I don't have to worry about shipping damage.

Having fun in the AR diaspora.

:rolleyes:

Roger

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Roger, there is a set (I suspect you already know) on the bay. Local pickup in Kentucky! Currently at $400. No reserve noted! 34 hours left in auction.

Those are LST-2's... he offered those before I think last year as I recognize the wall decor...

Update: they sold for $420 but it is a long drive to Kentucky for me and he works for the post office and refused to ship via any carrier so I'm sure that affected the sell price.

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  • 2 months later...

Well, the AR-7s finally arrived yesterday by slow-boat from China. Hey, they were picked up by a friend who decided to extend her stay.

Usual auction site issues:

1} I noticed on the woofer with the lighter cone (1974) the dust cap glue had deteriorated to the point where it could be lifted so I'm thinking I have another fried voice coil. Nope, no signs of heat damage. It seems to hang up though and the gap doesn't look centered. Turns out someone decided to drive these without any suspension and deformed the voice coils by bottoming them out. Oh, big do-do, hate the outcome of those impulse buys :) This pair has sequential serial numbers and I was hoping they were veneer. Turns out AR-7 sets have sequential numbers since they shipped as pairs in one box unlike ARs larger offerings which rarely have sequential numbers. The serial numbers on this pair are 16K+.

2) They are vinyl-coated and will need a veneer job should I decide I like them.

3) One knurled nut was missing.

Couldn't tell the date by cursory examination so I pulled the tweets -- April 1973. There are shades of Norwood even though the labels say Cambridge -- Sprague npe caps, 16AWG-105C wiring. Both woofers appear to have been replaced -- one in '74 and the other in the mid-80s.

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What to do? I doubt the seller would be willing to comp me for the woofers at this late date.

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Well, as they say, necessity is the mother of invention. The spiders were forgiving enough and the cones were strong enough to allow me to lift the vc's high enough to reshape the bottom of the formers. After about an hour or so of fiddling around they looked like they would fly so I foamed them.

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I found some interesting sealer at the bargain bin so I gave it a whirl. It is much softer than duct seal.

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Some measurements:

Spragues were 6.8 and 7.1MFD so I left them in -- didn't have any 6MFDs on hand and the AR-6's used tens anyway, besides npe's seem to read high on standard meters. ESR appears to be irrelevant in this application.

The stuffing weighed in at 8-ounces\per speaker.

DCR on these is around five ohms -- must have been ARs trick to coax a little more power out of the under-powered amps these were more than likely expected to run on.

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So I put them back together this morning and fired them up -- wow -- I'm impressed -- big sound, little speaker. I think they are keepers. The Adcom 555II is giving them a good workout at the moment.

I was also impressed by the difference in sound between the two woofers. The later iteration with the stiffer cone has a much more pronounced mid-range which could almost be balanced using the flat/normal switch which I believe knocks down the highs by 3db.

The label mentions using them in a "quad" system :)

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Very nice little speakers, and somewhat similar to my pair of 7's - - - my tweeters are dated June '73 and have s/n's of 20XXX, but the woofers are Tonegen replacements :( and I also have the unattractive vinyl :angry: which significantly reduces their LQ (love quotient).

The light colored woofer certainly looks early and original, and even if dated '74, may have been paired up with '73 tweeters. The dark cone woof also looks original but a slightly different iteration - - is it stamped with a date?

Tried to follow your diagnosis, but how can you be so sure that both woofers have been abused? And the Sprague caps? - - like yourself, I am often inlined to want to keep the originals but both of your measured values have already drifted beyond 10% of original crossover design, which would make me consider replacement.

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Very nice little speakers, and somewhat similar to my pair of 7's - - - my tweeters are dated June '73 and have s/n's of 20XXX, but the woofers are Tonegen replacements :( and I also have the unattractive vinyl :angry: which significantly reduces their LQ (love quotient).

The light colored woofer certainly looks early and original, and even if dated '74, may have been paired up with '73 tweeters. The dark cone woof also looks original but a slightly different iteration - - is it stamped with a date?

Tried to follow your diagnosis, but how can you be so sure that both woofers have been abused? And the Sprague caps? - - like yourself, I am often inlined to want to keep the originals but both of your measured values have already drifted beyond 10% of original crossover design, which would make me consider replacement.

The date on the darker woofer is smudged and my best guess is '85.

A visual on the voice coil formers revealed the damage first discovered when I was trying to shim the coil and the shim would not seat on one side. I was not able to photograph it without an extra pair of hands. Removing the spider was not an option.

The recent capacitor thread leads me to believe all measurements made on npe's will be higher than actual. The AR-6 uses the same drivers and has a 10MFD cap so I wasn't too concerned about the tolerance at any rate.

They are still cranking. I blew two fuses so I had to turn the volume down :)

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Roger ...Who's the vendor you used for those Foam surrounds? Nice job

McPeak at MSound is usually recommended on this forum but he didn't have the preferred BA FF foams the last time I checked with him. These came from a lot that I got off the auction site from someone in Templeton, MA. Not as compliant as the BA's but they are not bad.

It seems one of the frequent issues with the smaller AR speakers is people trying to drive them at high volumes with the bass control maxed out so using the less-compliant foams on these may actually add to their longevity. The spiders on the original drivers may not be quite as resilient as they were originally.

Some of the later iterations of the 8" driver had gasket/spacers under the spider and basket rim. RoyC pointed me to the JBL foams for those to get a proper fit. It appears that was AR's fix for bottomed out voice coils as the additional thickness of the gaskets prevent this problem -- not sure how that affected overall performance.

I haven't used a BA foam on an 8" driver but like them very much on the 10" drivers.

Roger

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  • 3 weeks later...

....

Some measurements:

Spragues were 6.8 and 7.1MFD so I left them in -- didn't have any 6MFDs on hand and the AR-6's used tens anyway, besides npe's seem to read high on standard meters. ESR appears to be irrelevant in this application.

.....

Well, surprised no one challenged me on the esr statement since additional cap esr in series with a tweeter voice coil will reduce tweeter output. I think I will recap these one at a time while listening in between.

I blonded the AR-7's since the peeling vinyl was too painful to look at.

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Roger

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