"Brown Stuffing" and Potentiometer Corrosion

[johnieo]

Kenyonbm's observation that the old brown stuffing looked like rock wool was right on! We shared and analyzed samples and found that the brown stuff is indeed rock wool. Rock wool contains sulfur, which corrodes the silver plating on the potentiometer's brass and bronze parts. Once the proective layer is gone, local heating and moisture take over and finish the job -- much worse on some pots than on others.

The details of this joint effort are described in an MSWord attachment.

The conclusions for me are to:

(i) refurbish / replace the offending potentiometers;

(ii) replace rock wool with fiberglass of the same weight.

This would only be a concern in early models that were designed with both potentiometers and "fiberglass" stuffing. I'll bet coffee that this corrosion will not re-appear, unless one lives downwind from a rock wool smoke stack, or near a sulfur mine!

Cheers

1678.doc

[dynaco_dan]

Hi John;

This report took my breath away it is so thorough.

Thank you very much to all three investigaters.

[charger3834]

Very interesting ! It has always been a mystery to me why AR's from the 1960's have so much more pot trouble than their 1970's counterparts.

[Carlspeak]

All readers of this post who are anxious to dive into their speakers and remove that old stuffing are cautioned to wear a face mask when handling rock wool. There are numerous medical studies on the net regarding safety issues with breathing in rock wool fibers.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[JoeB]

This paper definitively answers an important question. It belongs in the library for easy access. Awesome!

[kenyonbm]

I agree that a face mask or respirator is a good idea when handling the rock wool. I would also suggest some gloves as it is very itchy. That is the one of the properties that suggested that it was rock wool and not fiber glass. (the others are smell, coarseness and coloration)

I came across this while researching rock wool:

Tulane University Study on Rock and Slag Wool

The most comprehensive morbidity study (one that researches the causes and effects of diseases) of rock and slag wool workers was conducted by researchers at Tulane University who reported no increase in respiratory symptoms and no evidence linking respiratory symptoms to exposure to rock and slag wool fibers. A more recent update of this study again found no lung abnormalities that could be attributed to rock and slag wool fiber exposure. Evaluation of chest X-rays and lung function tests indicated a generally healthy population; any observed abnormalities were attributed to smoking habits. In summarizing the results of these studies, the researchers stated in 1992: "We have concluded that after 10 years of these investigations, we have failed to demonstrate an adverse effect of man-made vitreous fiber exposure on respiratory health. We have found workers in this industry to be generally healthy, without any detectable evidence of occupationally induced disease." Results from two European studies of rock wool workers are consistent with the Tulane study's findings.

Here is a link to this quote and other information.

http://www.naima.org/pages/resources/safety/research.html

Ken

[RoyC]

>I'll bet coffee that this corrosion will not

>re-appear, unless one lives downwind from a rock wool smoke

>stack, or near a sulfur mine!

John,

I won't be taking you up on that bet, though I would gladly buy all three of you coffee for sharing a most interesting study:-)!

I have a fair number of formerly corroded AR pots out there in restorations that were completed more than a few years ago, and have always used the later AR yellow fiberglass or new fiberglass when re-installing the stuffing...And now that you mention it, I have personally experienced no recurring problems, nor have I received any reports of pot trouble from folks for whom I have restored speakers.

I also have a large collection of uninstalled pots that were cleaned in the past two years. They are still looking good.

You guys may be on to something!

Roy

[Guest Eunomians]

Very very nice post. Thank you for the wonderful information!

Cheers

[Carlspeak]

>I agree that a face mask or respirator is a good idea when

>handling the rock wool. I would also suggest some gloves as it

>is very itchy. That is the one of the properties that

>suggested that it was rock wool and not fiber glass. (the

>others are smell, coarseness and coloration)

>

>I came across this while researching rock wool:

>

>Tulane University Study on Rock and Slag Wool

>The most comprehensive morbidity study (one that researches

>the causes and effects of diseases) of rock and slag wool

>workers was conducted by researchers at Tulane University who

>reported no increase in respiratory symptoms and no evidence

>linking respiratory symptoms to exposure to rock and slag wool

>fibers. A more recent update of this study again found no lung

>abnormalities that could be attributed to rock and slag wool

>fiber exposure. Evaluation of chest X-rays and lung function

>tests indicated a generally healthy population; any observed

>abnormalities were attributed to smoking habits. In

>summarizing the results of these studies, the researchers

>stated in 1992: "We have concluded that after 10 years of

>these investigations, we have failed to demonstrate an adverse

>effect of man-made vitreous fiber exposure on respiratory

>health. We have found workers in this industry to be generally

>healthy, without any detectable evidence of occupationally

>induced disease." Results from two European studies of

>rock wool workers are consistent with the Tulane study's

>findings.

>

>Here is a link to this quote and other information.

>

>http://www.naima.org/pages/resources/safety/research.html

>

>Ken

Studies may show rock will is not a carcinogen. Hoever, keep in mind this material is inorganic. Once you breath it into your wind pipe and lungs it's going to stay there until you die.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[johnieo]

>Once you breath it into

>your wind pipe and lungs it's going to stay there until you

>die.

Not necessarily; depends on a lot of things. See article attached by a guy I did some work with a a few years ago:

http://www.buffalo.edu/news/fast-execute.c...rticle=64090009

Obviously, we're all going to work safely with any fiber, but this material isn't asbestos.

[dynaco_dan]

Hi John;

Carl makes a very good point.

I would suggest anyone contemplating removing or working with it, treat it as if it was asbestos and use all necessary safety means.

Rubber gloves, safety googles and at least a paint mask and do it outdoors.

We must do things as safely as we can.

[Carlspeak]

>>"Once you breath it into

>>your wind pipe and lungs it's going to stay there until

>you

>>die.

>

>Not necessarily; depends on a lot of things. See article

>attached by a guy I did some work with a a few years ago:

>

>http://www.buffalo.edu/news/fast-execute.c...rticle=64090009

>

>Obviously, we're all going to work safely with any fiber, but

>this material isn't asbestos."

Below is an exerpt from the EPA web site regarding studies conducted on rock wool, fiberglass in ceramic fibers. They put rock wool into a safety classification which is more serious than fiberglass.

http://www.epa.gov/ttn/atw/hlthef/finemineral.html

"Technology Transfer Network Air Toxics Website

EPA Home > Technology Transfer Network > Air Toxics Website > Fine Mineral Fibers

Fine Mineral Fibers

Hazard Summary-Created in April 1992; Revised in January 2000

Fine mineral fibers include glasswool, rockwool, slagwool, glass filaments, and ceramic fibers. There is no information available on the acute (short-term) effects of fine mineral fibers in humans. Glasswool, rockwool, and slagwool administered by inhalation produced little pulmonary fibrosis in animals. Two epidemiological studies did not show a relationship between occupational exposure to glass mineral fibers and adverse clinical signs or mortality. Studies in humans have shown mixed results regarding exposure to glasswool, glass filaments, rockwool, and slagwool and an increase in cancer. Animal studies have not shown an increase in lung or respiratory tract tumors from exposure to glasswool, rockwool, or slagwool by inhalation, while animal studies have shown mixed results from exposure to ceramic fibers. The International Agency for Research on Cancer (IARC) has classified glasswool, rockwool, slagwool, and ceramic fibers as Group 2B,:-( possibly carcinogenic to humans, and glass filaments as Group 3, not classifiable as to their carcinogenicity to humans.

The study goes on further to say:

Cancer Risk:

Glasswool:

A study of glasswool workers in the U.S. showed a slight increase in mortality from respiratory cancer, however, this increase was not statistically significant. (2)

A European study showed no overall excess mortality from lung cancer related to glasswool exposure in humans. (2)

A study of Canadian glasswool workers showed a substantially increased mortality from lung cancer, which was statistically significant, but was not related to time since first exposure or to duration of exposure. (2)

In inhalation studies in rats, there was no significant increase in lung tumors from exposure to glasswool, however a few respiratory tract tumors occurred. (2)

EPA has not classified glasswool for carcinogenicity.

IARC has classified glasswool as Group 2B, possibly carcinogenic to humans. (2)

Glass filaments:

There was no increase in respiratory cancer among glass filament workers in the U.S. and no increase in lung cancer in the European workers. (2)

No statistically increase in tumor incidence were seen in experiments in which glass filaments of relatively large diameter (>3 µm) were administered intraperitoneally to rats. (2)

EPA has not classified glass filaments for carcinogenicity.

IARC has classified glass filaments as Group 3, not classifiable as to their carcinogenicity to humans. (2)

Rockwool and Slagwool:

A study of rockwool/slagwool workers in the U.S. indicated a statistically significant increase in mortality from respiratory cancer. (2) :-(

In a study of European workers, there was an overall, statistically nonsignificant increase in lung cancer among rockwool/slagwool workers. (2)

In two studies in which rats were exposed to rockwool by inhalation, no statistically significant increase in lung tumor incidence was seen. (2)

In an inhalation study of slagwool in rats and hamsters, no increase in the incidence of respiratory tract tumors was reported. (2)

EPA has not classified rockwool or slagwool for carcinogenicity.

IARC has classified rockwool and slagwool as Group 2B, possible carcinogenic to humans. (2)....."

The study you referenced to apparently concerns a new glass fiber reinforced with aluminum that Rockwool Corp developed. Below is an excerpt which, I believe, indicates Rockwool Corp. developed the new fiber to address safety concerns with old-style rock wool.

".........The UB researchers have found that once this glass fiber, known as RIF (HT), is inhaled, its long strong, glass fibers are broken down into smaller pieces outside of cells, apparently through the same mechanism that the body uses to break down old bone. The smaller pieces, they found, then are safely ingested and digested by cells.

"These findings violate everything that is known about the laboratory chemistry of these glass fibers," said Robert Baier, Ph.D., UB professor of oral diagnostic sciences, director of the UB Industry-University Cooperative Research Center on Biosurfaces (IUCB) and principal investigator on the study.

The finding goes a long way toward solving a puzzle that has perplexed chemists and regulators for a decade, since a Danish company, Rockwool Corp., developed RIF (HT), which is very strong, but does not persist in the lungs........."

Now, why would Rockwool Corp. devote resources to developing the RIF (HT) material?

I just wanted to add the above information in an effort to advise classic speaker enthusiasts of the potential harmful effects of handling vintage stuffing materials.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[dynaco_dan]

Hi again;

My comment for safety was regarding the Rock Wool only, or it's equivalent.

After giving more thought to it, use it for fibreglass as well.

As an apprentice, I worked quite a bit in the heating trade with asbestos, without any knowledge of it's potential danger or with safety equipment.

Knowing what we now know, use safety equipment, so that you can teach hifi to your grand children.

[pmsummer]

All the more reason to get it out of those boxes. Thanks!

But what's the best alternative? Fiberglass/ Acousta-Stuf? Something else?

[dynaco_dan]

Hi there;

If you are not removing a driver, and servicing the crossover, then there is absolutely no need to remove the insulation, assuming it is fiberglas that you are referring to.

If it is the Rock Wool and the pots are an issue then removal and replacement is a good idea.

Only will removing a driver tell you which insulation you may have inside.

TomT or others may correct me on this comment, maybe only the earliest AR's used Rock Wool as a filler.

Ending when and which models?

I see in my local lumber yard that there is now more than just bags of fibreglass bats for home insulation.

They are in different bags now, I will have to take a closer look at the ingredients next time I'm there.

They all appear to be soft bat type fibreglass, but is it?

If it is different for our application, then we will be reading more about this subject, I am sure.

I have read bits and pieces about poly material, a pound of fibreglass in not the equivalent to a pound of poly.

Of course only the bass is going to be affected by improper materials or amounts.

I don't think that there is a more than a few members that could test out a woofers influence with changing materials and quantities.

Carl's name comes to mind first.

Of course, Ken Kantor, but that would be imposing upon his valuable time and resources.

Without proper test equipment, we would, on an average, really short change ourselves, by our just guessing on amount and different materials.

Unless someone has read test reports, where speaker insulations were changed either in volume or materials.

[johnieo]

>But what's the best alternative? Fiberglass/ Acousta-Stuf?

>Something else?

If you are referring to speakers originally stuffed with rock wool, it is fiberglass. AR began with fiberglass. Tom Tyson showed me a photo of the inside of his AR-1, Serial Number 006 to illustrate that fact. For some period in the sixties AR used rock wool in some speakers, then returned to fiberglass.

One should restuff it with the same weight as the rock wool that was removed. AR-4x I have examined that used the same crossover coil had identical weights of rock wool or fiberglass. No experimentation or data taking is necessary.

You might consider searching old posts; this is a well discussed subject so will not consume more of Mark's storage in repetition. The bottom line, as Ken Kantor noted, is that there is no "drop-in" replacement for fiberglass in speakers that were designed around fiberglass. A few notes of the lowest bass will be lost if a polyester fiber is substituted in those speakers.

cheers,

[dynaco_dan]

Hi John;

Thank you for that information.

[kkantor]

Hi from China...

I'm happy to do this kind of testing, provided it doesn't duplicate much effort already done in this area over the years. Here's some food for thought:

http://auralization.blogspot.com/2006/05/c...tial-stuff.html

-k

kkantor.spaces.live.com

[dynaco_dan]

Hi Ken;

Thank you very much for posting that very informative write-up.

It certainly shows that a pound of fiberglass is not equal to a pound of any poly.

[Carlspeak]

>Hi from China...

>

>I'm happy to do this kind of testing, provided it doesn't

>duplicate much effort already done in this area over the

>years. Here's some food for thought:

>

If a study is done, I'd like to see melt blown polypropylene (MBPP) added to the list of fibers. They are smaller in diameter than most fiberglass fibers and lower in density thus yielding more surface area per lb. And, they are about 6 time smaller in diameter than conventional polyester fibers.

Glass wool and DE glass are in the 4-7 micron range. Whereas, MBPP is in the 2-6 micron range.

MBPP is used extensively in filtration applications for that very reason.

I suspect the 'tortuous path' of the fiber mass behind a woofer is key to lowering Fc. Stuffing density would be adjusted by the difference in their inherent densities (e.g. a lb. of MBPP would contain many more fibers than a lb. of glass fiber).

An added benefit of MBPP is its inherently safe polymeric nature as opposed to any type of glass.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[zcon67]

Hi all,

I'm new to this so if I am stepping toes please forgive.

Started building in the early 70's. No rock wool was being installed at the time, just fiberglass: Owens corning, pink and John Mansville, yellow. In opening 2 pr of ar5's they were vertually identical with the exception of the 4uf cap made by different companies and both filled with yellow. The serial #s are approx 4400 apart. Can I assume this fiberglass was made by John Manville since I can recall no other brands?

I did go to both sites to see if they had any real info as to the makeup of there fiberglass and came up empty. However John Mansville did have a more informative site included here:

http://www.jm.com/corporate/labs_services/2321.htm

It did have a contact and wondered if anyone with real expertise in this area had contacted them or had interest in doing so. Maybe they would be willing to convey some of their real science to compare.

PZ

[kenyonbm]

Hi PZ

Could you tell us if the rheostats in the fiberglass stuffed units were corroded?

If the source of the corrosion is the sulfur containined in the rock wool, then the fiberglass filled unit should not have the same problem unless the fiberglass also contains sulfer.

Ken

[zcon67]

Hi Ken,

I haven't completed the 4th speaker yet but the 3 that I have opened have been in very good condition as far as the corrosion. I had one other problem with one pot,a plastic key for the wiper was broken so I installed an Ohmite that was suggested here. I am going to assume the last pot will be in good condtion also. If not I'll let you know.

PZ

[Shacky]

Thank you very much Mr. O'Hanlon!

I have a project pair of 2AX's from '70's that had excellent original pots. I cleaned them up and used them in my '65 2AX's and put the rock wool back in place. Think I might open them up and change that combination.

Some folks on audiokarma found source for new 15 ohm ceramic pots. Wonder how they would hold up with the rock wool?

[johnieo]

>Some folks on audiokarma found source for new 15 ohm ceramic

>pots.

Shacky:

The Aetna-Pollak pots were wound on ceramic; that material is not the problem.

If you would, please tell us the source of the pots found on Audiokarma and their power rating.

> Wonder how they would hold up with the rock wool?

If made from silver-plated bronze/brass/copper, likely no different than original.