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Old 3rd April 2009, 04:10 PM   #1
cchean is offline cchean  United States
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Default Mcintosh amps transformer rewinding, help needed please!

Hello,

My brother in law has a pair of McIntosh MI-75 monoblock amps and he asked me for help. One of them is blowing fuses and his technician said the output transformer is shorted. OK, I called Audio Classics in NYC and another McIntosh authorized service center and they told me they charge $600 to rebuilt the damaged transformer. They also said this part is no longer available. Any other options? Do you know anyone outside the Mcintosh network that perform this kind of service? I guess McIntosh Service Centers or dealers charge a flat fee of $600 for this kind of service. Any advice will be appreciated. Thanks.
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Old 3rd April 2009, 04:17 PM   #2
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hey-Hey!!!,
See Heyboer TX in Grand Haven MI. They've got great skill at rewinding vintage output TX's. They've done some very complex Peerless designs for me( reverse engineering to make copies of a single sample ). With a rebuild like you propose, you'll probably use the original cores( C's IIRC), and re-pot them in its original can. Very reasonable prices too.

With the McIntosh multi-filar primaries, wire insulation is important; maximum thickness is required.
Cheers,
Douglas
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Old 3rd April 2009, 11:13 PM   #3
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If you go this route, please, ask Heyboer to document the winding process for future rebuilds!
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Old 3rd April 2009, 11:57 PM   #4
llwhtt is offline llwhtt  United States
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I had Mercury Magnetics rewind a MI-200 OPT a few years ago, they charged $750 for that job. The MI-200 OPT has 3 separate C-cores on one bobbin and runs at approx. 1000VDC. They had to order special mag wire and such for the high voltage. I would think the MI-75 would be less of a job.

Craig
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Old 4th April 2009, 11:03 PM   #5
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Quote:
Originally posted by llwhtt
I had Mercury Magnetics rewind a MI-200 OPT a few years ago, they charged $750 for that job. The MI-200 OPT has 3 separate C-cores on one bobbin and runs at approx. 1000VDC. They had to order special mag wire and such for the high voltage. I would think the MI-75 would be less of a job.

Craig

hey Craig,
Your core description makes me curious. I can see a single pair of C's arranged to approximate a torroid, or two pairs like an E-I...but three pairs makes no sense at all to me. Care to elaborate?
cheers,
Douglas
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Old 4th April 2009, 11:28 PM   #6
Apex Jr is offline Apex Jr  United States
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I had bought a McIntosh MI 350 and found it had a
blown output transformer.
I had brought it over to Bob Hovland to check it out.
He recommended me to go to a guy in Wisconsin.
I can't remember who it was...You might try a google search.
It cost me 1000.00 to have it redone.

Steve @ Apex Jr
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Old 5th April 2009, 03:37 AM   #7
llwhtt is offline llwhtt  United States
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Douglas,

I'll try to explain it, if you were to look down on the square paper bobbin from above (windings horizontal) there would be a complete core on the left, on the right and one perpendicular to the first two, top or bottom. I saw it with my own eyes, even hooked it up to check it out before they potted it. The can(box) it goes into must be at least 7" on all sides. We think they just used cores they had on hand and used as many as it took to do the job and it took three. Definitely was NOT the most elegant way to do it but you have to remember this was an industrial amplifier not high end. Hope my explanation is clear enough, if not I'll to draw some diagrams.

Craig
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Old 5th April 2009, 08:25 AM   #8
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Quote:
Originally posted by llwhtt
Douglas,

I'll try to explain it, if you were to look down on the square paper bobbin from above (windings horizontal) there would be a complete core on the left, on the right and one perpendicular to the first two, top or bottom. I saw it with my own eyes, even hooked it up to check it out before they potted it. The can(box) it goes into must be at least 7" on all sides. We think they just used cores they had on hand and used as many as it took to do the job and it took three. Definitely was NOT the most elegant way to do it but you have to remember this was an industrial amplifier not high end. Hope my explanation is clear enough, if not I'll to draw some diagrams.

Craig
Diagram please. I am curious.

Thx,
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Old 5th April 2009, 08:42 AM   #9
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Here's a picture of a three-pase C-core transformer. If the last core and bobbin are removed, you get a triple C-core transformer with primary and secondary windings in separate bobbins.

Not what you described, but I cannot picture the third "perpendicular" core...
Attached Images
File Type: png transformermodel.png (38.5 KB, 739 views)
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Old 5th April 2009, 08:46 AM   #10
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Quote:
Originally posted by Bandersnatch



hey Craig,
Your core description makes me curious. I can see a single pair of C's arranged to approximate a torroid, or two pairs like an E-I...but three pairs makes no sense at all to me. Care to elaborate?
cheers,
Douglas
I think I got it...

The cores are arranged in the form of in inverted "T" with each segment being a core. ASCII art below:

_|_

The intersection point of all three cores goes thru the center of the bobbin.
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