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AR3aImproved rebuild


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I received AR3aImproved pair in original factory shipping cartons yesterday. They seems to be fairly original and working, even LF alignment is a bit loose to my taste. Anyway, rebuild seems to be quite straight forward, but I have couple of questions.

Teak molding has some cracks near upper corner of right speaker, cracks may be visible on the pictures. Have you any experience which glue might be most suitable for repair due oily nature of teak? Even other than BLO finish on Teak is not too obvious, it would also be nice to know were other finishing methods used for Teak.

Woofer surround seems to mounted on masonite ring. What is purpose of this ring? Why woofer frame was not pressed deep enough in the first place. Or was sheet metal not flexible enough for contour needed for free movement of surround?

As 12" cone weight is considerable, some sag of spider can be expected. Is it good idea to reverse woofer mounting position? This way spider will sag towards correct shape. When new surround will be assembled, will this cause some trouble as old spider in new position will most likely flex back quite soon.

Best Regards

Kimmo

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Hi Kimmo,

Any problem with LF will be because of the perished surrounds. I would only play them very softly in that condition - if at all.

Ordinary wood glue should do the moulding if cracked right through. Scrape any excess when dry.

I have had good results with teak after sanding very lightly and applying Briwax. It can be bought with subtle colouring as well as clear.

Nice speakers ! Hope this helps.

Mike

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VERY nice specimens, Kimmo!

A good re-foam job is all the woofers need. AR woofers were intentionally built to be very compliant, which is why the cabinet seal is important. It is the basis upon which "acoustic (or "air") suspension" speakers function. Rotating the woofer in the cabinet won't hurt anything, but is not necessary.

The masonite ring provides the proper height of the surround relative to the cone. Do not remove it when cleaning off the old foam! The use of the mounting ring probably had something to do with ease of manufacturing. Later versions of the woofer, manufactured for AR by Tonegen in Japan, had a raised area stamped into the basket instead of the masonite ring for mounting the surround.

Roy

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  • 2 weeks later...

I have now removed drive units from cabs without too much trouble. Woofer and mid range backsides were coated with some white colored deposits, that you can see from the first picture. I suppose that this is some kind of oxidation. As I have not seen this kind of residue before, any ideas why this has been happened and what can be done to avoid this happening again would be appreciated.

Crossover can not be described to have tidy layout. From pics you may note attention paid to fine detail, stuffing material has been used as insulation to avoid rattles and shorts between coil wires. Bracing can not be considered too effective. Side and back panel braces are not glued to each other to reinforce back panel seam and hard wood was not used for bracing. I coated all internal seams with PVA-glue to be sure that cab will be airtight when finished.

Crushed corner and cracked front panel moldings needed some work before I was able to clean the cabs properly. I wet sanded the cabs with 400 grit paper to remove dirt and some of the BLO used in the past. It seems that there was quite thick layer of BLO on the cabs. Sanding was followed by rub with with steel wool and BLO. After this I wiped BLO and some more patina from the cabs with cotton cloth. Cabs are not finished yet and do have some patina, but look fairly clean to me.

Best Regards

Kimmo

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I have now removed drive units from cabs without too much trouble. Woofer and mid range backsides were coated with some white colored deposits, that you can see from the first picture....

Crushed corner and cracked front panel moldings needed some work before I was able to clean the cabs properly. ..

Kimmo,

Almost looks like salt corrosion but who knows. Clean it off with soap and water and put some type of anti-corrosive protection on, an anti-corrosion lube or a lacquer would probably do the trick. If it is a salt the water will neutralize it.

The coils wires are lacquer coated and do not require additional insulation unless constantly rubbing against something which is why the stuffing is used to keep it separate.

The sailing boys use epoxy to fix furniture damage. It can be mixed with sawdust or it is capable of filling gaps on its own. You may want to practice on something else if you have never used it before. Set times are variable and it can be worked while green. Definitely a challenge if you have never used it before though. You can also make fillets with it to reinforce the bracing.

Roger

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The corrosion "may" be cadmium oxide. I'm not at all sure about that but if it is it's highly toxic. Use caution removing it and don't breathe it in. Here's more: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7898&hl=cadmium

Roger's description of using epoxy is something we've discussed here. I like JB Wood Weld, dyed with Mixol #22 "tobacco". John O'Hanlon recommended the epoxy/Mixol approach and it works very well. CSP member RoyC prefers the Mohawk epoxy sticks available from good woodworking supply stores. It's very convenient. Comes in a "Tootsie Roll" shape and you just slice off a piece and knead it in your hands, then press in place. It also has the advantage of coming in a variety of colors.

The fine sawdust (like from your sander's dust bag) mixed in regular epoxy works well too. Just remember it will turn darker when mixed into the epoxy. The "2-Ton" or slow drying epoxy works better than the 5-minute kind. Your cabinets are teak (and looking really beautiful!) so the #22 would be too dark. Attached are before and after photos of a corner bash on my AR-3s, repaired with epoxy.

For more explanation of the epoxy technique, see page 9 of my KLH Model Eight booklet, attached to Post #1 here: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6387

-Kent

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The corrosion "may" be cadmium oxide. I'm not at all sure about that but if it is it's highly toxic. Use caution removing it and don't breathe it in. Here's more: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7898&hl=cadmium

Roger's description of using epoxy is something we've discussed here. I like JB Wood Weld, dyed with Mixol #22 "tobacco". John O'Hanlon recommended the epoxy/Mixol approach and it works very well. CSP member RoyC prefers the Mohawk epoxy sticks available from good woodworking supply stores. It's very convenient. Comes in a "Tootsie Roll" shape and you just slice off a piece and knead it in your hands, then press in place. It also has the advantage of coming in a variety of colors.

The fine sawdust (like from your sander's dust bag) mixed in regular epoxy works well too. Just remember it will turn darker when mixed into the epoxy. The "2-Ton" or slow drying epoxy works better than the 5-minute kind. Your cabinets are teak (and looking really beautiful!) so the #22 would be too dark. Attached are before and after photos of a corner bash on my AR-3s, repaired with epoxy.

For more explanation of the epoxy technique, see page 9 of my KLH Model Eight booklet, attached to Post #1 here: http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=6387

-Kent

Nice references, Kent. I wasn't aware of the toxic cadmium issue. I will take some time and research the best remedial treatment.

Roger

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Those are really gorgeous speakers, Kimmo - - - it appears that it is rather common for Euro-AR's to be clad in teak. I know I've personally never seen teak AR's in the U.S. - - a large majority of our cabinets are veneered in American Walnut. Further, I believe that UK manufactured AR's may indeed utilize English Walnut, which has a different appearance from our species.

This crystalline corrosive build-up on the backside of speaker drivers is somewhat worrisome, and I am surprised that I have not seen this phenomenon more thoroughly documented or corroborated. If this does indeed represent exposure to a hazardous condition, we should all become aware of how best to handle these components, learn to neutralize and remove the deposits, and maybe even figure out how best to minimize or eliminate future corrosive activity. Any chemists out there?

Not long ago, I found a similar white and dusty build-up on the backside of a 40 year-old Smaller Advent woofer magnet and basket.

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Those are really gorgeous speakers, Kimmo - - - it appears that it is rather common for Euro-AR's to be clad in teak. I know I've personally never seen teak AR's in the U.S. - - a large majority of our cabinets are veneered in American Walnut. Further, I believe that UK manufactured AR's may indeed utilize English Walnut, which has a different appearance from our species.

I agree, even both speakers do have quite similar looking veneer due close serial numbers. On www.hifiloudspeakers.info pages it was discussed how difficult it was to make specs for veneer matching of Kef Reference series speakers. Some years ago I made new cabs for 1976 Kef Cantata kits, you can see from the first picture how nicely walnut veneer can be matched. When cabs has to be made from pre veneered board, things will get more complicated. Quite many AR original models here in Finland were finished in Koto wood. Koto is quite similar to Birch, which has been popular here since 50´s.

I have now tried to find out the reason for white residue. If it is supposed to be caused by cadmium plating, then the woofers and mids must be cadmium plated, which is most unlikely. Then I figured if the cab stuffing material has been wet when installed and cabs have been in cold warehouse before sale, fungus might have grown on some surfaces. As you can see from pics, there are some white powdery deposits still on one cab inside wall. Even woofer has bee now cleaned, some deposits can be seen and area behind cone has some surface rust. One woofer cone seems also be somewhat speckled. There is also some kind of musty odor near speakers. This seemed not too obvious in the first place as there were no water marks on the speakers.

Best Regards

Kimmo

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...

I have now tried to find out the reason for white residue. If it is supposed to be caused by cadmium plating, then the woofers and mids must be cadmium plated, which is most unlikely. ..

Yes, very nice looking speakers, both pairs.

Cadmium was definitely used in the past but I'm not sure how much of a danger it is in a sealed container. If it bothers you I would just overcoat it with a paint or sealer. One of the links below mentions chromates. I haven't seen any zinc chromate primer in years though. I would probably just use Rustoleum Hi-Temp flat black and a brush to seal it. I thought I noticed a little whitish powdering on the back or a 1972 vintage woofer today. Not enough to bother me though. The fiberglass bothers me more.

These links have more info on how and when cadmium was used:

http://www.cadmium.org/pg_n.php?id_menu=11

http://www.finishing.com/176/12.shtml

Cheers,

Roger

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From the second link posted by Roger, at least these two statements should make everyone sleep a bit more soundly. :(


Cadmium is a chronic, cumulative poison like lead and mercury. It isn't safe to try to deal with these corrosion products except at a plating shop which recognizes the hazards and has the necessary protective gear and medical monitoring programs.


As mentioned, cadmium is a bio-accumulating poison. For that reason I would not use a Dremel or polishing pad or other method that might spread cadmium dust around.
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I have now tried to find out the reason for white residue. If it is supposed to be caused by cadmium plating, then the woofers and mids must be cadmium plated, which is most unlikely.

Does anybody know if AR speaker baskets and magnet assemblies were plated with zinc, nickle, cadmium or some other material in mid 70´s?

Best Regards

Kimmo

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I've seen the powder on many old drivers. Wiping with ordinary vinegar works very well to remove it. Whatever it is, don't lick it or snort it and all will be good.

The old fiberglass poses a greater hazard. I use a common disposable N95 mask, and try to handle it outdoors whenever possible.

Roy

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The veteran technician (50 years) at the shop for which I do speaker repairs http://stereowksp.com/repair.htm

just showed me an example of cadmium "whiskering" in a radio from the 40's. It does not look like the powder on the back of speaker drivers. Cadmium plating back in the 40's would sometimes result in short circuiting in radios when this occurred. Tin and zinc plating largely replaced it in the 50's.

He said the powder on the speaker baskets is not cadmium. It is more likely to be a product of zinc oxidation.

http://www.zink-nickel-kft.com/rust-corrosion.html

Roy

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the powder on the speaker baskets is not cadmium. It is more likely to be a product of zinc oxidation.

Good news! Sorry if I caused unnecessary worries :unsure:

Kent

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Phew! Household vinegar to the rescue once again! This thread was quickly about to enter The Twilight Zone, and while I can state that when I licked the "dust" off my Advent woofers I was expecting sweetness more like confectioner's sugar, my taste buds were definitely screaming "heavy metal". :P

Thanks again, Roy - - - the Hazmat teams have been sent home.

Still, inquiring minds wonder what causes this to occur in the first place - - chemicals in the wool/glass stuffing?....moisture in the presence of electricity?..... sealed boxes with no place to escape?.... volume controls set to eleven? While zinc is possibly the most common element used to inhibit corrosive action on steel fabrications, it does appear to have a somewhat symbiotic relationship to cadmium.

Cadmium occurs naturally in zinc ores and is obtained as a byproduct of zinc smelting. It is used as a component in low melting point alloys and as a corrosion-resistant coating on other metals

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.... Tin and zinc plating largely replaced it in the 50's.

He said the powder on the speaker baskets is not cadmium. It is more likely to be a product of zinc oxidation.

http://www.zink-nickel-kft.com/rust-corrosion.html

Roy

I think that is more likely and a lot less toxic. From the msds table salt (sodium chloride) is more toxic than zinc oxide so if you are into licking your drivers I don't think you have a problem...

Toxicological Data on Ingredients:
Sodium chloride: ORAL (LD50): Acute: 4000 mg/kg [Mouse].
Zinc oxide: ORAL (LD50): Acute: 7950 mg/kg [Mouse]
Cadmium: ORAL (LD50): Acute: 890 mg/kg [Mouse].
Even fiberglass doesn't seem to be a major health problem. I'm sure I've breathed my share over the years.
This from Washington State Public Health:
In 2000, the National Academy of Sciences reviewed studies of fiberglass manufacturing workers and concluded that "...glass fibers do not appear to increase the risk of respiratory system cancer." In 2001, the International Agency for Research on Cancer said that "glass wool", which is a form of fiberglass, is not classifiable as a human carcinogen. Deaths from lung diseases, including lung cancer and mesothelioma, in groups of workers involved in the manufacture of glass wool, are not consistently different from what is found in the United States general population.
So you can smile when you get the itch to open up a speaker cabinet. <_<
Roger
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This thread was quickly about to enter The Twilight Zone, and while I can state that when I licked the "dust" off my Advent woofers I was expecting sweetness more like confectioner's sugar, my taste buds were definitely screaming "heavy metal". :P

Ah, classic Spinal Tap! :) It may be tme to dust the oxide off that dvd and watch it again.

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I'm the original poster who brought up the cadmium risk.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7898&hl=cadmium

All I can tell you is that a potentiometer I had extracted from a HK speaker was covered with the white powdery subtstance. I gave it to a PhD chemist who tested it in his lab (which shall remain nameless, but I'm from Minnesota...MMM, who could it be?) with the proper instrumentation. It's cadmium. That's not speculation. Read the original post. It was a pretty concentrated dose of the stuff too, not just a white powder with "traces" of the stuff. In that era they did used cadmium as a corrosion treatment, but apparently in the intervening years, it's broken down. It's highly toxic either through skin contact or when it becomes airborne.

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I'm the original poster who brought up the cadmium risk.

http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=7898&hl=cadmium

All I can tell you is that a potentiometer I had extracted from a HK speaker was covered with the white powdery subtstance. I gave it to a PhD chemist who tested it in his lab (which shall remain nameless, but I'm from Minnesota...MMM, who could it be?) with the proper instrumentation. It's cadmium. That's not speculation. Read the original post. It was a pretty concentrated dose of the stuff too, not just a white powder with "traces" of the stuff. In that era they did used cadmium as a corrosion treatment, but apparently in the intervening years, it's broken down. It's highly toxic either through skin contact or when it becomes airborne.

I think you are overstating the hazard. Look again at the LD50 for cadmium above. Now if you were working around it in a plating operation everyday there would be cause for concern. My guess is that you are getting a higher exposure to it your food.

You can also spray suspected componenst with clear shellac to reduce exposure. The shellac would be easily removable at a later date if desired.

Roger

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What era HK speaker? There is no reason to believe the driver baskets or speaker cabinets are full of cadmium based on one experience. Still it is good to know it may be around.

Cadmium residue is well known to be associated with old electronic equipment, but I agree with Roger. Standards of this type are based on occupational exposure, and significant absorbtion through the skin is a bit of a stretch, especially in the world of a speaker hobbyist.

Roy

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Ah, classic Spinal Tap! :) It may be tme to dust the oxide off that dvd and watch it again.

When I was at BA, we did a really great subwoofer, called the PV1000. It was pretty compact (about 15" per side dim), used a 1000-watt BASH amp and BA's truly excellent Pro Series car sub driver (2" VC, cast aluminum basket, very long excursion, low FS, etc.), along with a very massive passive radiator.

It was a great sounding and great-looking sub, with a real cherry veneer cab and a nice front panel control arrangement.

We were very proud of its performance. Being both the Prod Devel director and the head of home audio Mktg, I had great lattitude in how we did things, what they sounded like and what we called them.

I knew of the Spinal Tap "11." But the PV1000 had such great output capability, that I decided it needed to go to "12."

Steve F.

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Ah, classic Spinal Tap! :) It may be tme to dust the oxide off that dvd and watch it again.

I knew of the Spinal Tap "11." But the PV1000 had such great output capability, that I decided it needed to go to "12."

Steve F.

Wow, not 1, but 2 louder...amazing! :D

What years were you with BA, Steve? My current computer speakers are A60's (Series II).

Roy

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Roy,

Yup, two full louder. That's how good it was!

I was there from '92-'03.

The A's were gone by then. The bookshelf HD5, 7, 8, 9, and 10 and floorstanding T830/930/1030 were in the line when I got there.

We replaced the HDs with the CR (Compact Reference) line, the T's with the VR (Video Reference) line and intro'd the Micro90 sub-sat family, which was an amazingly good line of product. Absolutely blew away every other sub-sat offering out there, including all the various Bose AM-3/5/7 stuff and the Cambridge Soundworks stuff at the time. The MR90 became BA's best-selling product in its history, by far. Put a lot of coin in the owner's pockets.

In mine? No. All I did was do the market research, conceive and define everything about the product, co-design it (looks and utility), define its engineering targets and specs, work with Eng to develop it, voice it, and then do all the ads, owner's manuals, packaging, dealer training guides and marketing. Other than that, I was barely involved.

We also did the very good VR960/965 and VR970/975 towers w/built-in powered subs (at that time--mid-to-late '90's, Def Tech had popularized the "Powered Tower"), and then probably the very best products BA did while I was there--the superb VR-M ("Monitor") series: the VR-M50 and 60 bookshelf spkrs, and the VR-M80 and 90 floorstanders.

I'd put the VR-M's up against anything in their size/price class, and they were the speakers that I felt unreservedly proud of having done, much the same as the AR guys undoubtedly felt about the Classic models.

But the owner of BA was an original Advent guy and he knew of my affection for AR. Like politics and money at family dinners, we always kept a polite distance on the subject of things like the 2ax/3a vs. the Large Advents, etc.

Steve F.

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