Observations on the Rebuilding of a Pair of AR-5's

[Guest baumgrenze]

I am working on a pair of AR-5's I purchased at an estate sale. They carry the serial numbers 30533 and 30543. The tweeter in the former is stamped with the date 12/13/72, so the speaker must have been assembled sometime shortly after that date.

In a previous post today I outlined by rationale for mounting the crossover network outboard on the back of the speaker cabinet. That work for this set of speakers is ongoing.

I'd like to comment on some observations I've made along the way and ask some questions about proposed solutions.

I've attached a photo of the Industrial Condenser Corp. 1307: 4uf 50V capacitor as I found it inside the cabinet. It had been placed on a small piece of what must have been urethane foam which was now a gooey black liquid. Was there a good reason for 'shock mounting' this capacitor? I'd like to suggest that a small scrap of closed cell polyethylene flooring underlayment might make a longer lasting replacement if it is really needed.

I've observed that the recess for the woofer mounting is not as carefully worked as was the mounting in my AR-2AX's, even though they were a less expensive line. I've attached 2 photos that show a large, unfilled void where there was a knot in an inner ply of the plywood. Also, the router used to make the recess must not have been freshly sharpened, or the tech sought to get the job done as quickly as possible. There are several places near mounting holes where the wood tore out and was not filled. One of the T-nuts was pulled through so that it protrudes above the surface of the mounting. I did not hear these speakers when they were new. I could not play them when I bought them; the foam suspension was rotted out. Given that a thin foam gasket was used to make the acoustic seal, I wonder just how good the acoustic suspension really was. I will fill the gaps with a good quality epoxy putty I've been using on my house, a also grind the T-nut flush. Has anyone an opinion as to whether on not replacing the original thin gasket with the Ace rope caulking is a good idea? I am leaning in that direction. See the two attached photos.

The tweeters in these speakers have proved problematic. One arrived at Millersound today for evaluation. One of the hair fine leads just outside the dome is broken. I've attached a photo of it and also of the second, which appears to be 'diseased.' The small dome is attached down by 3 small brown dots. In the case of the tweeter with the broken lead it appears to be a clear brown color. I marked it with a yellow letter V to show where the break is. In the case of the second tweeter there are whitish lumps on the brown. I took the photo of this tweeter through a multifocal magnifying glass. I hope it is not too confusing. The small circle closest to the handle is a higher magnification section of the lens. Has anyone else seen this 'disease' phenomenon? Can anyone say with certainty that it is 'trouble?' Also, what is the 'generally accepted' description of this tweeter, should I need to seek a replacement for one or both?

Thanks,

baumgrenze

[Guest Bret]

There is a really good post, somewhere, addressing the sealing of the cabinet. . . complete with all sorts of wonderful pictures and instructions and do's and don't's .

It's here, somewhere. You can try the "search" function and look for "putty" and "wood putty" and other terms until the cows come home. I couldn't narrow the search enough to find it, even though I know the author!

Rope caulk is probably too thick. The baskets will bend too easily with something that non-pliable. There is a version of putty sold at Parts Express that comes in rolls that's cheap, easy to use, and probably a better option. You don't want too much under the woofer, but you can get a better seal with that than trying to re-use those gaskets that have obviously seen better days. Just don't put down too thick of a line of caulk and then get torque-happy or you can bent the basket. (been there, done that) Yes, a seal is important. A Titanic hull "weld" really isn't necessary.

Nice photos, BTW, but I really have trouble with the close-up of the suspension foam on the tweeter. I can't really tell what I'm looking at because of the differing magnifications and there's not quite enough resolution to see a broken wire. But if I'm seeing what I think I'm seeing, I've never seen that before. Weird.

[joelongwood]

I've resealed quite a number of vintage AR speaker cabinets, and have found this stuff (Pug Duct Seal) to work extremely well. In appearance and in workability, it's just about an exact match for the stuff AR used originally. It can be rolled into a shape thinner than a pencil which is ideal for placing behind the woofer frame. It can be purchased on-line or at just about any hardware store. I got mine at Ace.......costs around $2 for enough to do about a dozen cabinets. Hope this helps.

[dynaco_dan]

>I've resealed quite a number of vintage AR speaker cabinets,

>and have found this stuff (Pug Duct Seal) to work extremely

>well. In appearance and in workability, it's just about an

>exact match for the stuff AR used originally. It can be rolled

>into a shape thinner than a pencil which is ideal for placing

>behind the woofer frame. It can be purchased on-line or at

>just about any hardware store. I got mine at Ace.......costs

>around $2 for enough to do about a dozen cabinets. Hope this

>helps.

>

>

Hi Bob;

I will agree with your sound advice regarding this particualr electrical putty.

In our Home Depot in Vancouver, it is only a few dollars for enough to do dozens of speakers.

I wrote previously of finding locally, this was confirmed by the past AR warantee depot owner last week, 3M Dum-Dum or autobody putty in pencil strip form.

It may have also been packaged as, Mortite, or other names and sold by other sources.

I bought a package back in the late '60's, from an auto supply house and still have some left, and most of it is still soft and suptle.

I say most of it, because of the exposed edges and heat from being in my office all those years caused a slight drying effect.

It is still available, or at least it's current equivalent, and I bought a new package, about $30.00 CDN and another similar material for about the same money.

This material is identical to the early AR dark putty, the other product I bought is a black shiny putty, still both in pencil in strips and appears to be the current autobody putty of choice here judging by the scarcety of the original and availablity of the newer.

My point is, each package has enough strips to supply Carl for years and it would be wasteful for the normal user and it's ten times the price.

For some on like Carl that may service a number of drivers every day, the autobody putty would be faster and more consistant for production work.

Coverage wise, they both are probably the same weight.

The electrical putty has the body and texture, slightly grey colour, only longevity is the un-known, if it should harden with age.

Being used and approved for use as an electrical sealant, I can't see it hardening, at least, crumbling and falling out, in our lifetime.

Before leaving this subject I must remind members not to use toilet or plumbers putty, I've seen the long term effect, not in our best interest.

[soundminded]

>I am working on a pair of AR-5's I purchased at an estate

>sale. They carry the serial numbers 30533 and 30543. The

>tweeter in the former is stamped with the date 12/13/72, so

>the speaker must have been assembled sometime shortly after

>that date.

>

>In a previous post today I outlined by rationale for mounting

>the crossover network outboard on the back of the speaker

>cabinet. That work for this set of speakers is ongoing.

>

>I'd like to comment on some observations I've made along the

>way and ask some questions about proposed solutions.

>

>I've attached a photo of the Industrial Condenser Corp. 1307:

>4uf 50V capacitor as I found it inside the cabinet. It had

>been placed on a small piece of what must have been urethane

>foam which was now a gooey black liquid. Was there a good

>reason for 'shock mounting' this capacitor? I'd like to

>suggest that a small scrap of closed cell polyethylene

>flooring underlayment might make a longer lasting replacement

>if it is really needed.

>

>I've observed that the recess for the woofer mounting is not

>as carefully worked as was the mounting in my AR-2AX's, even

>though they were a less expensive line. I've attached 2 photos

>that show a large, unfilled void where there was a knot in an

>inner ply of the plywood. Also, the router used to make the

>recess must not have been freshly sharpened, or the tech

>sought to get the job done as quickly as possible. There are

>several places near mounting holes where the wood tore out and

>was not filled. One of the T-nuts was pulled through so that

>it protrudes above the surface of the mounting. I did not hear

>these speakers when they were new. I could not play them when

>I bought them; the foam suspension was rotted out. Given that

>a thin foam gasket was used to make the acoustic seal, I

>wonder just how good the acoustic suspension really was. I

>will fill the gaps with a good quality epoxy putty I've been

>using on my house, a also grind the T-nut flush. Has anyone an

>opinion as to whether on not replacing the original thin

>gasket with the Ace rope caulking is a good idea? I am leaning

>in that direction. See the two attached photos.

>

>The tweeters in these speakers have proved problematic. One

>arrived at Millersound today for evaluation. One of the hair

>fine leads just outside the dome is broken. I've attached a

>photo of it and also of the second, which appears to be

>'diseased.' The small dome is attached down by 3 small brown

>dots. In the case of the tweeter with the broken lead it

>appears to be a clear brown color. I marked it with a yellow

>letter V to show where the break is. In the case of the second

>tweeter there are whitish lumps on the brown. I took the photo

>of this tweeter through a multifocal magnifying glass. I hope

>it is not too confusing. The small circle closest to the

>handle is a higher magnification section of the lens. Has

>anyone else seen this 'disease' phenomenon? Can anyone say

>with certainty that it is 'trouble?' Also, what is the

>'generally accepted' description of this tweeter, should I

>need to seek a replacement for one or both?

>

>Thanks,

>

>baumgrenze

Having removed a pair of woofers from a pair of AR2as to replace the capacitors and clean the pots, I don't think I'd ever replace the sealant with putty. The original AR putty was so tenacious that it was nearly impossible to remove. It was like glue. It took me several hours with an improvised right angle tool to scrape enough of the old putty out so that I could pry the woofers loose without damaging them. I never did manage to get the midrange sub enclosure out and I'm not even thinking about the tweeter. Putty works by forming a bonded air tight seal but has no elasticity. It undergoes plastic deformation. Foam on the other hand does have elasticity, is easy to use, inexpensive, and doesn't stick in the same way. It releases when you want it to and need it to. Here's some from Parts Express designed specifically for this job.

http://www.partsexpress.com/pe/showdetl.cf...tnumber=260-542

My AR9s came with just this type of foam sealing material on the woofers.

I agree with you about the internal crossover networks being a weak design choice. It was one of the quirks Henry Kloss incorporated in early AR speakers and like lemmings, engineers have used it as their standard method ever since. Henry Kloss was a great pioneer of audio but he was not a great manufacturing engineer. Before AR invented a speaker requiring an air tight enclosure, it was a simple matter to remove a few screws from the back of a speaker cabinet and get at the insides. But the requirement for an air tight seal changed everything. We've discussed just how air tight an acoustic suspension speaker needs to be but I recall one ad where AR engineers were testing and AR3 enclosure for air tightness so it is very important. So is the stuffing. When the fiberglass was first installed, it was undoubtedly laid in neatly before the baffleboard with the drivers were installed. The stuffing plays a critical role in the dampening of the woofer's inherent resonance, not only the amount but the way it is packed. When a sealed acoustic suspension has to be repaired, you have to work through the woofer opening in the baffleboard and you either have to push the stuffing out of the way or you have to remove it altogether. Good luck trying to get it back to where it was before you disturbed it. While the initial cost of installing an external crossover network would have been greater, this would have been offset by savings on in-warantee repairs. In fact, a defective crossover network could have been a plug out-plug affair in matter requiring a few minutes of technician labor at a dealer instead of several hours and shipping the entire speaker both ways to the factory or to an authorized service center. Furthermore, it would have facilitated later upgrade kits such as conversion of an AR3a to something akin an AR LST. That's life.

[Guest baumgrenze]

Thank you everyone for your input thus far.

I used the Ace Rope Caulk Weatherstrip product because I found it recommended in a thread here:

Sealing drivers in older AR cabinets

Topic started by johnieo, Nov 23rd 2005 (9 replies)

Last modified by tysontom, Jan 13th 2006

It seems to be a tractable enough product. It comes as a roll of 6 adjacent 1/8" ropes of a soft putty. You can see what a single rope looks like in the first photo in my 'external crossover' post:

http://www.classicspeakerpages.net/dc/dcbo...nt&file_id=2103

As I searched, I found that someone else mentioned 'plumber's putty' but seemed uncertain about what it is. It is a putty made from plaster of Paris and linseed oil. I'd not recommend using it as a long term sealant.

I used the rope caulk to remount the woofers on my AR-2AX's. I was careful where I laid it before I placed and screwed down the woofer. I have photos of how the original seal was placed. I'm not confident that it worked all that well. Because of placement, portions of it were not deformed or flattened from the original circular cross section at all. I'll bear in mind the risk of deforming the frame. With the 6 bolt 2AX's I was careful to do the tightening down after the fashion of installing the wheel on a car, criss-crossing and keeping track so that each bolt was tightened some before I started another round of tightening

Bill at Millersound did reattach the fine lead on the tweeter, but he then learned that the coil is fried. He reports that he gets a reading of 0.8 ohms across the terminals. My other tweeter reads 6.7 ohms. He reported back that he can point me to a 'replacement' but that it is one with the terminals on the back. At $35, the price is not exorbitant if, in fact, it will work with the existing crossover. Comments, anyone?

Thanks again,

baumgrenze