AR-4 details

[ra.ra]

 

My first pair of AR-4's was documented here.

 

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7264

  

Several months ago, I acquired a second pair of AR-4 speakers (s/n 07XXX) awaiting some re-hab attention, and just recently after I had begun to de-construct them, I was coincidentally contacted by a friend and local CSP member to tell me that he had recently obtained a pair of AR-4's. We have begun to share some thoughts and observations, and that discussion has prompted me to start this thread simply to add to the information base. Inside the cabinets, nothing unusual at first glance, but a few items caught my attention:

a. capacitors - - exactly like others I have seen in AR-4's, but both of these actually have an AR4 designation in their labels. Coincidence or meaningful?....I dunno.

 

b. coils - - my multimeter is unable to measure inductance but, unlike my other pair of very early AR-4's (s/n 00105 and 00242) that have #4 coils (200 turns), these speakers appear to have coils with more wire, and I suspect they are #5 coils (225 turns). I have confirmed that they weigh very near nine ounces, which would jibe with Tom T's coil chart data.

 

c. pots - - again, they look very typical, but a few small details of note. On the outside metal, they're stamped as simply Pollak (not Aetna-Pollak); and on the ceramic, there are not any 1, 2 and B designations. On the inside, I had never encountered a situation where the mineral wool fibers had penetrated the pot enclosure, and of greater interest, each of these pots has a double pot sweeper - one has a flat tip and the other has the typical dimpled tip. The startling thing, however, was that these pots were nearly perfectly clean - - nary a hint of tarnish or corrosion on the coils, disks, or sweepers, which I found highly unusual.

 

More to come as progress ensues and I sort thru some additional pics.

 

 

[owlsplace]

Nice ... looks like the extra wiper was designed to improve contact surface tension ... probably no drop-outs even with the rock wool fibers.

Roger

[iso]

As far as I remember my euro AR2ax did also have these double sweepers or tension springs too.... I think that 2 of the pots did have similar arrangement with springs like you, but tensioning springs were not nicle plated. Other two simply did have 2 exactly similar wipers (contact tip for center and outside track) stacked one abowe other.

Ea. of my AR2ax speaker did also have different coils... difference in coil inductance and weight was considerable. I unwound maybe 25-30 turns from higher weight coil and wound this over underwound coil. Coil weights were similar after this and inductance figures did matc very well too, even absolute figure was a bit too low. Both coils did have similar colour markings... only logical assumption is that coil winding accuracy was not too good. I suppose that rev counters were used, but maybe operators had to decide when to stop winding... and when someone tells a joke, operator may underwind or overwind coil or two.

Best Regards

Kimmo

[Carlspeak]

Ra Ra, you didn't mention the woofers. I bought a pair of 4x's with similar woofers with the lines on the cones and orange surrounds. The surrounds had become petrified. I mean petrified. They crumbled when touched.

How are yours?

[ra.ra]

Oops......don't know why the text in post #1 is so large - - I don't mean to be screamin' at you!

I cannot really explain the pristine condition of these pots, but Roger's comment is accurate - - these dual-sweepers have a very satisfying contact feel when the spring is compressed after the pots are re-assembled. The sensation is not loose or wishy-washy at all, but also not so tight as if they are scraping away with every turn of the manual control.

About the woofers (and tweeters), all of the drivers are in excellent condition - - some pics attached after clean-up and re-wiring for installation. The cloth surrounds remain pliable, and I have applied one light coat of Roy's butyl sealer probably two months ago. This is a similar experience to my first pair of AR-4 woofers (dated June 1964, without cross-hatch), which were also in great shape and fully restorable.

I feel like I have heard this story of Carl's petrified surrounds, and I can only think those must have experienced some brutal exposure or storage conditions to undergo that sort of transformation. The fiber in these surrounds - - - what is it, cotton or linen? - - - didn't the Egyptians use a similar fiber for wrapping mummies? I also have a third pair of these woofers - - like Carl, from an odd version of AR-4x speakers - - which was noted in this thread where I received much help figuring out this assembly.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7798

[ra.ra]

Just a brief progress update on this project. I wanted to show a final pic of the cleaned-up pots before they went back together, as well as a couple views of the freshened cabinets which show a particularly fine range of veneer grain patterns. Crossovers are next, then testing and re-assembly.

Carl, did your pair of 4x's mentioned in post #4 have the double cap (20uF and 24uF) and the coil with 265 turns?

[iso]

Your pots must have been super clean in the first place?

Cabs look very nice too...

Best Regards

Kimmo

[ra.ra]

Just a couple brief items.

After having worked on a fair number of older AR cabinets, for the first time recently I have experienced one of the t-nuts losing its grip on the wood baffleboard (first pic), so I'd like to ask how others have solved this problem. The tweeter screw just kept spinning in place, and I had to go in through the woofer hole just to be able to get at the t-nut, and it was not easy. Re-installing the original nut will now have to rely on chemical adhesion rather than a mechanical attachment, so is some sort of epoxy the best solution? Specific product and procedure? Further, is there a type of epoxy which has enough flow that it can be daubed on the backside of existing nuts to prevent this from happening again? When these nuts do become loose, I can see it being near impossible to get inside a speaker box without damaging a driver or cabinet.

Second, a couple thoughts about unwanted dark cabinet stains. As I was working on the AR-4's of this thread, I also spent some time refreshing the cabinet finish from my first pair of 4's, which are shown below in this post. For the record, I am not one who frets about every scratch or tiny chip or blemish in 50 year-old veneer - - I don't immediately reach for the orbital or palm sander - - but I do like the speaker cabinets to be attractive within a room setting. The dark stains were lightened using a slurry paste of an everyday household product, Bar Keeper's Friend (mfr'd. since 1882), which contains a mild formulation of oxalic acid (i.e. wood bleach). It is very easy and gentle to use for this purpose.

pic 1 - cabinet top as purchased

pic 2 - two years after initial restoration (natural oil only), some new sun bleaching has shown up

pic 3 - after first application of BKF slurry

pic 4 - after second application of slurry, before wiping clean

pic 5 - after re-finish with tinted oil, shadow of dark stain far more acceptable

[JKent]

Great tip! (BKF) In fact, I have some in the house and will give it a try (too bad I just bought a 5 lb bag of oxalic acid).

For the T-nut you might use one of the epoxy sticks. They're available in Home Despot etc. http://www.sears.com/j-b-weld-8258-kwikwood-epoxy-putty-stick/p-SPM7197586503?hlSellerId=8878&sid=IDx20110310x00001i&kpid=SPM7197586503&kispla=SPM7197586503

You just cut a slice and knead it in your hands, then press it into place. Sort of like modeling clay. I think it may work in both cases mentioned. It doesn't flow--you just press it into place.

-Kent

[xmas111]

I don't remember what pair of AR speakers I was working on but the pots had the double wipers. Even with the double wiper they weren't worth even trying to repair.

Rob, your restoration is coming along nicely. Those cabinets look very professionally refinished, nice job.

I'm looking forward to see how you do with the crossovers.

Keep up the great work.

[owlsplace]

Just a couple brief items.

After having worked on a fair number of older AR cabinets, for the first time recently I have experienced one of the t-nuts losing its grip on the wood baffleboard (first pic), so I'd like to ask how others have solved this problem. The tweeter screw just kept spinning in place, and I had to go in through the woofer hole just to be able to get at the t-nut, and it was not easy. Re-installing the original nut will now have to rely on chemical adhesion rather than a mechanical attachment, so is some sort of epoxy the best solution? Specific product and procedure? Further, is there a type of epoxy which has enough flow that it can be daubed on the backside of existing nuts to prevent this from happening again? When these nuts do become loose, I can see it being near impossible to get inside a speaker box without damaging a driver or cabinet.

Second, a couple thoughts about unwanted dark cabinet stains. As I was working on the AR-4's of this thread, I also spent some time refreshing the cabinet finish from my first pair of 4's, which are shown below in this post. For the record, I am not one who frets about every scratch or tiny chip or blemish in 50 year-old veneer - - I don't immediately reach for the orbital or palm sander - - but I do like the speaker cabinets to be attractive within a room setting. The dark stains were lightened using a slurry paste of an everyday household product, Bar Keeper's Friend (mfr'd. since 1882), which contains a mild formulation of oxalic acid (i.e. wood bleach). It is very easy and gentle to use for this purpose.

pic 1 - cabinet top as purchased

pic 2 - two years after initial restoration (natural oil only), some new sun bleaching has shown up

pic 3 - after first application of BKF slurry

pic 4 - after second application of slurry, before wiping clean

pic 5 - after re-finish with tinted oil, shadow of dark stain far more acceptable

t-nut.jpg AR-4 cab bleach (orig+) 1.jpg AR-4 cab bleach 2.jpg

Nice job with BKF. The ear on the tweeter nut has been flattened. It should be perpendicular to the base.

Roger

[ra.ra]

Kent, I think you are right that some of that kneadable epoxy putty should probably do the job once it sets up, and Roger is also correct about the pointy (Spock?) ears that seem to have been flattened. I will try to bend them back to perpendicular before re-installing to maybe get some new "bite" in the wood, but I will also use an epoxy of some type. Belt and suspenders... a man can't be too careful.

As I thought about this t-nut issue, I recalled one of my very favorite speaker restoration threads for vintage New England rarities. If you have not yet fallen asleep before post #224 where I found this image, you will pick up many excellent procedural tips here. For those who enjoy attention to detail, this guy's work is superb.

http://audiokarma.org/forums/index.php?threads/klh-model-28-rare-find-restoration.577202/

And to xmas111, your gorgeous crossover creations have inspired me to do better. Pics to follow soon.

[ra.ra]

Here's hoping everyone is having a very good Thanksgiving holiday. One thing I am thankful for is that I was finally able to complete one of my many long lingering unfinished projects. The t-nut problem was successfully repaired with the two helpful suggestions in posts #9 and 11 - - the ears were straightened (perpendicular) and I also slathered a little two-part epoxy on the outer sleeve before re-inserting to the baffle back and then pulling it tight using a C-clamp.

Beyond getting the refurbished speakers' performance to sparkle again, my objectives with the crossover re-build were two-fold: to use up some available parts on-hand; and to make an attempt at a newly organized arrangement resulting in an aesthetic assembly of components. As noted in the previous post, the inspiration for this comes after seeing the fine work that xmas111 (John) showed us with his restorations of AR-4x, 2ax, and LST speaker models. Thanks, John.

This was my first time trying to do much of the preliminary crossover assembly outside of the cabinet, and I simply used a small scrap of 5/16" thick panel for layout and primary connections. I made an initial sketch to start the idea and then made minor revisions at most every step. The cap bundle is two 3.0uF 100V mylar caps (which were NOS from Boston Acoustics) with an added 0.68uF 200V Sprague HYREL. The combined measured value is precisely 6.0uF. From what I understand, the HYREL (for "high reliability") is essentially the same as the Sprague Vitamin Q cap, which remains very popular with vintage electric guitar enthusiasts. It is a paper-in-oil (PIO) cap with glass capped ends, and is purportedly lauded for its specific tone qualities.

Otherwise, the challenge was finding a neat arrangement for wire management, and I do like having these wires strapped to the cabinet back panel at various points, and before they extend to the driver terminals. Like I have done with some other projects, I simply re-used the original mineral wool stuffing, but topped it off with a thin layer of fiberfill under the woofer basket in lieu of the crumbled Kimpac (sp?).

[ra.ra]

And a handful of pics with drivers installed. My personal preference is always to refinish the walnut cabinets with a bit of "mahogany" color in the walnut, and I am also fond of using "blackboard" paint for the baffleboard panel. Also, I like to take great care in cleaning up the drivers before re-installing, and now I am tending to use very thin stainless steel washers underneath the screw heads - - not only does it look a bit more finished, but this provides a more secure attachment and keeps the turning screw away from the edge of the fabric surrounds.

[alkermes]

Nice work, ra.ra!

Thanks for detailing out your project with the photos and descriptions. You have a beautiful set of 4's.

[owlsplace]

Yes, nice piece of work ...

[DavidDru]

Great stuff RaRa! Looks fun with great results.

I especially liked the images of the cabinet tops using the Bar Keepers Friend. I picked up a can of it the other day at Ace after seeing so many having put it to good use over on AudioKarma. (Damn water stains) Those L1590's I recently got has a stain on the top of one of them.

Nice crossover too. Never even thought about if you could use a Pio and Mylar together like that. Clean looking. I was able to remove the crossover board on a pair of EPI M150's a couple weeks ago to work on it outside the cabinet and that was nice.

Good call on the blackboard paint. Good color and finish for this application. Has just a little old world feel to it as it should be. Plus you can write yourself a note!

One tnut gave me fits too the first time I removed the woofer on one of my AR3's. What a pain that was. Did the same thing with the epoxy. Glue and hope.

Grilles?

[ra.ra]

Yeah, the BKF is a great product around the house - - dirt cheap and very gentle. Also, try it for cleaning your best cookware or metal surfaces. It's been around for over 100 years, hails from my home state (IN), and was developed after a serendipitous kitchen experience cooking rhubarb, which contains oxalic acid. Not sure how the active concentration in BKF compares with hardware store wood bleach, but it has been surprisingly effective at minimizing the ugly dark water stains on several speaker cabinets for me.

The blackboard paint is the flattest finish I have found, and for a slight bit of contrast, I use a different black paint (satin, usually) with just a bit more sheen when touching up the driver surfaces. Speaking of chalk messages, it looks like I already have one from the original installers on the woofer cone!

IMO, the inclusion of t-nuts is the one small detail that make these early AR cabinets stand out, but once they lose their grip it can cause you fits trying to remove the drivers without causing damage. From here on, I'll try to remember to dab a smear of epoxy over the nut flanges when I have cabinets opened up.

There is no hard science involved with my cap choices here, but these are all high quality components. My hearing is probably not as keen as it once was and I have no sophisticated measuring tools or procedures, but this cap bundle was test-driven for a week (with no driver gasket and no cab stuffing) before committing to hardwire and solder. The cosmos will forever be divided on the theories and practicalities of "cascading" or "bypass" caps - - which was not necessarily an objective here - - I'm just using up some available parts and having a little fun with the re-build. These old speakers now look very good and sound terrific.

[ar_pro]

They look great - very well done!

The photo details of your work are also appreciated, and they will be an excellent resource for future restorers.

[iso]

Also, I like to take great care in cleaning up the drivers before re-installing, and now I am tending to use very thin stainless steel washers underneath the screw heads - - not only does it look a bit more finished, but this provides a more secure attachment and keeps the turning screw away from the edge of the fabric surrounds.

Truly nice speakers ra.ra

I have tried to find washers that do not turn when the screws are tightened, as they will be more gentle to surrounds than ordinary round washers. Square or oval washer may be what I have been looking for... but not found yet... any ideas?

Best Regards

Kimmo

[ra.ra]

Kimmo, nothing special about the washers, but I like these stainless steel ones because they are very thin, and you can see in the detail pics how they just cover the outer perimeter of the cloth surround, and it gives me a bit more confidence when tightening up these screws. By the way, I've used the pliable grey duct sealer (similar to original) to seal these drivers until it squishes out, and then neatly trim off the excess with an x-acto or very small screwdriver.

David, I just noticed you asked about the grilles. Two pics below show my temporary set-up for a test drive - - there is another stack spaced about 6 feet from these. I have these hooked up to an Adcom speaker selector (GFS-6) which is alternately connected to either a modest NAD receiver or a Scott solid state tuner and AR integrated amplifier. With the selector, I can easily conduct A-B (and C-D-E-F) comparisons from a single source. Here I am listening to the AR-4's noted in this thread (lower left); the very early s/n AR-4's shown in post #8 (lower right); and a fine pair of restored 4x's from 1970 (on top).

On the grilles, it may be a little difficult to see, but the lower right AR-4's have their original cloth which has a slightly more open weave (this issue has been discussed in these pages before). The 4x speakers (top) have very good original grilles, while the grilles on the 4's (lower left) of this thread have been replaced - - the originals were not salvageable.

[xmas111]

You did a beautiful job on those babies!

Your hard work certainly paid off on these. The cabinets look brand new and will look beautiful where ever you decide to place them.

Congratulations on rebuilding the crossovers. Very neat and professional looking. I especially like the layout/schematic you created. You have some great draftsmanship talent too.

I hope you've been able to take some time to sit and listen to them.......if so I'm sure it was quite enjoyable.

You should be very proud of your craftsmanship!

John

[VintageMan]

Nice job, great result!

Enjoy!