Magnet recharging centers

[Earl K]

> I'm pretty sure RobH is referring to Orange County ( OCS ) and Toddalins experiences with his alnico magneted , 2235 wannabees .

> All in all, these experiences all add up to another great reason to stick with ferrite magneted woofers.

[jw5115]

I didn't want to start thread on whether but on where.
Yes woofers are the most common. but if you have bought hundreds of compression drivers and just done the battery test;
you would have a reference for whether your old driver needs a boost. compare it to a much newer ferrite or Neo model
you will clearly hear whether your old driver is performing.
A mear 8-10% will make a big difference in an otherwise optimized system.
In over 200 - 2440,2441,2480,2482 motors that I have cannablized to make my field coil motors.
I would estimate only 10% of them were above 90% of spec.
I do have a gaussmeter with a probe thin enough for this measurement but it will not do the tweeters.
I just have to believe my ears on those
since most people do not have the advantage of testing their motors in the gap and that a slowly failing item in any system is so hard to identify.
"frog in the slowly rising temperature pan of water" If this thread is to continue along this path?? " so it shall"
But I just thought it would be a service to compile this list for the benifit of those who needed it.
jw5115

[grumpy]

It is helpful to know -both- where to go, as well as what to have explicit faith in.
The latter has been now illuminated in quite some detail. I agree it would be nice to
have several nearby options for Alnico recharging (with the proper polarity , who knew
to even ask?).

[Lee in Montreal]

A nearby source for remagging indeed greatly reduces "chances" to destroy compression drivers during shipping. Looks like I found a source less than an hour away.

[herki the cat]

I was about to delete my post #12 addressing Robh3606 to identify the Service Center of the two speakers that would not retain a full charge, but i found Earl K's link ....one example of why , " to not be blindly trusting....you will see That GPA's Bill Hanuuschak Altec's chief engineer went to great lengths to completely solve the mystery of the ages and completely rebuild those two speakers. Bill tried everything ultimately replacing the magnet with new parts and returning the defective magnet slug to the manufactuer for analysis. herki[Quote/]

[Lee in Montreal]

There was valuable info in this thread for a noob like me. Reverse polarity between Ferrite and Alnico. I am surprised though that drivers were reconed and shipped before any measurement or verification was done. And of course, all the costs associated..

Anyway, Now I know what to ask for when I bring my 2441s for demag/remag.

[Rudy Kleimann]

Lee, you missed something here. Perhaps in the translation from French to English?

The polarity is NOT different between the AlNiCo and Ferrite versions of a driver i.e. 2441 vs 2445,6,7. Or the Neodymium versions, for that matter. The same diaphragm fits all of these, and polarity has to remain the same.

The polarity reference was about North Pole/South Pole orientation when remagging an existing magnet. Mistakes can be made; it is possible to charge one the opposite direction, which would make that particular driver operate out-of-phase with normal drivers.


Hope this clears it up for you.

There was valuable info in this thread for a noob like me. Reverse polarity between Ferrite and Alnico. I am surprised though that drivers were reconed and shipped before any measurement or verification was done. And of course, all the costs associated..

Anyway, Now I know what to ask for when I bring my 2441s for demag/remag.

[Lee in Montreal]

Hope this clears it up for you.

No need to clarify. It was exctly what I understood from that post on the other forum.

[grumpy]

it is possible to charge one the opposite direction, which would make that particular driver operate out-of-phase with normal drivers.

The story wasn't entirely clear (as the units were entirely disassembled and magnets replaced, as well as setting the polarity of the
charging device properly), and it would be helpful to know... It would -seem- like the only ramification would be a reversed phase
(i.e., + to red pulls in vs. pushing out if the latter were normal) from a reverse-polarity recharge, and that the entire T/S spec would
still be measured as normal... Does anyone know for certain that charging magnetic materials in a magnetic circuit is a symmetric
property? Again, I would certainly expect so, but that is not my area of knowledge and the Altec 416 thread referenced above almost
implies that it is not... which seems weird.

[toddalin]

Yes, I took in three 2205s to OCS for conversion to 2235s and have them re-magged.

When I got them back I wasn't happy with the sound, lacking in the midrange. Grumpy came over and over a year later we tested one and came up with a BL of a bit over 18. I complained to OCS, and it was over a year later that they reshot the three woofers for no charge. We remeasured one and the BL was now about 22, which is a bit over spec. (But I still wasn't happy with the midrange so now attribute it to the 2235-design combined with room acoustics.)

When they "shoot" a speaker, they do not check it afterwards. They just figure that they've shot it to the point of saturation.

[Altec Best]

One should always excercise due diligence when dealing with GPA or any other reconer/remagnetizer ( ie; test your woofers before & after servicing ) .

Here's one example of why , to not be blindly trusting ( the story is a mammoth read ) .

<>

True Earl But as Herki the Cat has noted Bill is one of a few people who will go the extra mile to make things right.

http://www.hostboard.com/forums/f700...a-what-do.html Pano's Thread ! In which he says he was wrong, Bill still replaced the Alnico slug free of charge.

Bill's Reply
OK, here is Bill's reply to me about what he found with my drivers. Bill said OK to post this.

"When I received your speakers I found that one of them had to be reconed because the speaker was packed in a plastic bag and the edge had stuck to it damaging the cone."

(note from Pano - don't put your drivers in a plastic bag!)

"So I decided I would just tear them both down, when I did I measured the magnetic flux and it was 8.0 Tesla and the polarity was backwards, the Altec spec sheet rated it at 12.0 Tesla. So I then re magnetized it twice to reverse the polarity and bring the flux back up, however it did not, the polarity reversed but the flux stayed at 8.0. I then torn down both magnets and totally de-magnetized the parts, after re-assembling them and re magnetizing them there was still no change.
I then called my magnet vendor and spoke to their engineer, he told me that I should have no trouble magnetizing the Alnico whether I torn it down or not and that Alnico should not even loose it magnetism unless it was dropped or the plates slide."

"Next I measured and weighed your magnets and the ones I currently use and they were the same and agreed with the Altec spec 2.4 pounds. So the only thing I could think of was trying a brand new piece of Alnico in your structure from my stock and when I did the gap flux went up to 10.5 to 11.0 Tesla which is lower then what Altec states but I believe to be what it needs to be."

(note from Pano: I measure a BL of 12 on each, so right at spec).

"I am now going to send in your slug of Alnico to the magnet manufacturer to let them analyze it to see why it will not magnetize. This is for my interest."

"I did not get a chance to do the T/S parameters the guys shipped it out before I had a chance. But I think it will be ok with the higher gap flux that is matched and the coil DCR is also matched."

[tesla]

Rudy,

I havew been to OCS severtal times, and is not that big of an outfit.

Who and where was the "faulty" recharging done?

Based on their history, reputation, and personnel, I have a hard time believing Great Plains Audio would be the culprit. OCS, maybe, simply because they are a big outfit and mistakes can happen, but they've been around too long to not have heard about this before. And, as has already been pointed out, the actual flux cannot be checked with a cone and coil in place.

I have 2 pair of 12" AlNiCo that I suspect are suffering from overpowering demag and have often wondered myself about this service and if it could be done without removing the cones.

Someone with personal experience with remagged drivers, esp. with cones installed, please chime in here and lay this gossip to rest. The shop name, tech. name, and approximate date of the remag. would be appreciated. PM me if you prefer not to post on the thread.


I recall a thread post somewhere quoting G.Timbers performing a "Q modification" by briefly and intentionally overpowering a test woofer that seemed to be overdamped, saying "that's about right" after retesting, rather tongue-in-cheek. Couldn't find the post, but it was a rare moment of humor, to be sure...



Thanks,

Rudy

[herki the cat]

THE RCA MONSTER MAGNETIZER

Rudy, Originally Posted by Rudy Kleimann ....Based on their history, reputation, and personnel, I have a hard time believing Great Plains Audio would be the culprit....I recall a thread post somewhere quoting G.Timbers performing a "Q modification" by briefly and intentionally overpowering a test woofer that seemed to be over damped, saying "that's about right" after retesting, rather tongue-in-cheek. Couldn't find the post, but it was a rare moment of humor .... thanks ,Rudy. I have been to OCS several times, and is not that big of an outfit.

tesla;325969 Your post is right on! Nothing in my reply here is rebuttal what so ever. Any way I am very interested to learn about G.Timbers ...experience with Q modification. I searched the forum and came up with 75 posts, Yikes!

Strange thing about "over charging" speaker magnets. In RCA Camden we had a huge magnetizer in which i had the opportunity to recharge several RCA Photphone RCA Compression Drivers & Mi-9449 woofers, Altec 515 B Speakers, certain Microphone magnets, Disc Recording heads, & .

This RCA factory charger was a monster 6 feet tall by 7 feet wide, constructed with two huge Power Transformer "w" lamination stacks of cross section 8 inches square, assembled as you would see in a transformer. The center piece of the top "W" was cut off from the Top "W" member so it could be moved up & down by a motorized system to provide the space for the magnets being charged.

The magnetic winding dc current was ramped up and down slowly by remotely changing the Camden Plant DC Generator field current, requiring approx' 30 seconds to prevent fly back oscillation due to coil LC __L x 1/(DIxDT) surge oscillation which would otherwise discharge the magnets severely.

I know for a fact this monster was so powerful that polarity reversal was not a factor for the magnets in hand.

This suggests that a more modest charger incapable of completely discharging an existing opposite polarity or the current ramping is not adequate to prevent coil oscillations.

New Jersey people don't know where to stop. RCA Princeton Labs extremely powerful magnetizer was once improperly loaded and it let go of the work piece punching a huge hole right through the wall.

Community Light & Sound Inc., Near by, now has this babe and they refuse to work on any product except their own.

I know for a fact that Western Electric in all of their post WW-2 speakers used an extremely small permanent coil with extremely low shunting stray capacity in all of their magnetic structures which would not support a very high frequency fly back oscillation due to the magnetic iron Q.

The only problem was to disconnect the coil from the huge bank of capacitors after the zap accomplised its task; so a precision disconnect fuse was implemented to isolate the huge capacitor bank. This system typically requires a 55,000 ampere pulse.

The RCA 44-BX Broadcast studio Microphone magnetic structure also was charged with a one half cycle 60 HZ shot into three turns of 1/2 inch diameter multi-strand conductor via a huge Ignitron switching vacuum tube in a huge GE Inc. ,cabinet full of complicated control circuitry.

Here, the huge 100 pound 60 Hz transformer had a name plate rating of 55,000 amperes with a secondary three quarter turn winding, 3 inch wide by 3 inch thick stack of 0.060 inch copper foil laminated sheets.

RCA also used ramped AC current to completely demagnetize all speakers completely for any rework.herki[Quote/]

[Rudy Kleimann]

Here's a link to another thread right here on the LHS forum:

http://www.audioheritage.org/vbullet...ture&highlight=

Great pictures of a hand-built magnetizing machine for drivers at a speaker repair shop in MA.

Thanks to LHS member Pelly3S for posting the pics. Perhaps this Shop could be added to the list of remag service locations?


I found it reading the thread Earl K posted the link to on another forum.