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What's involved in rewinding a Transformer?

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toddbailey

New Member
Hi All,

A output transformer recently failed (McIntosh MA-230) and so far the only shop I found who said they could rewind it wants far too much for the task.

After all it's only a few hundred feet of wire right?

I'm thinking worse case, I could carefully dissassemble the transformer, mark the parts to insure an orderly reammembly,
remove the core and unwind it until I find the failed winding, or just replace everything and start new.

I'll need to build a jig with a turn counter and secure a source for the enameled wire. Pretty simple if you ask me. So why is this guy asking $600 for the job? It's a pretty basic transformer with 4 or 5 separate windings, but nothing really special.

Is there something they didn't teach us in basic electronics?

thanks

thanks
 

MikeMl

Well-Known Member
Most Helpful Member
Baking it to reflow the Formvar insulation?
 

tcmtech

Banned
Most Helpful Member
got any actual specs to go with that transformer?

Input and output volts and what not.
I personaly have no idea what a McIntosh MA-230 is.
 

Sceadwian

Banned
Depends entirely on how the transformer is constructed todd, and how closely you need to match the old transformer. Honestly I'd find out what the specs are on the tranformer and just buy a new one.
 

toddbailey

New Member
Well, that is the $10,000 dollar question, can a live one be found?
this little jewel has several windings, a taped cathode and plate a fb winding and outputs at 4 8 and 16 ohms. I couldn't phantom a guess on all the volt or current ratings are but driving a pair of 7591 tubes maybe 500 volts plate at 250 ma? You'd think some sort of protective circuits would have been incorporated?

Anyway I hope the Mac has a replacement available, it's going to be a cold day in hell before I drop 600 to have it rewound.

BTW: the Mac ma-230 is one of mac's earlier tube amps and has the usual sound quality found on these hi spec amps.

If someone knows of any links they care to share on transformer rebuilding, I'd like to know what I am up against.

thanks
 

Sceadwian

Banned
Good luck =) Wouldn't hurt to call around to a few places or see if you can find details on exactly how it's wound. Stuff like that is very diffcult to find because they just don't make it (or very little) anymore.
 
Last edited:

toddbailey

New Member
Thanks already on the case.

One thought, If exact replacement can't be found, using the popular 7591 tubes and producing 35 watts, I could possibly rewire the amp to use say Eico's st-70 circuit design,
already found a pair of those transformers on ebay for 100,

I'd rather not butcher the amp in this manner but it is an option...
 

stevez

Active Member
Hammond makes output transformers and it seems that many of the transformer designs are relatively common. While they aren't cheap I would say they are affordable. I googled on "hammond transformer" and several sites with potentially good sources came up.
 

toddbailey

New Member
Hmmm,
Formvar insulation,
bifilar/trifilar winding methods,
flux densities

It's a variation of lions and tigers and bears, oh my.


I hope Mac Labs has something off the shelf, I just might have to take up drinking again to get through this one...
 

tcmtech

Banned
Most Helpful Member
Mouser Electronics carries some and so does Parts Express.
They both have a bunch of output transformers to chose from.
And the prices are rather reasonable too!
 

Diver300

Well-Known Member
Most Helpful Member
Transformers & Rectifiers Ltd - Design and Manufacture of Transfomers and Transormer Rectifier Equipment.

They made me a transformer a few years ago. It was 200 V ac line - neutral in and out, 3 phase in, 6 phase out, with an auxiliary 5 V 3 phase out. It was rated at about 500 W and it cost me about £200. It weighed about 15 kg, IIRC

I know it cost me a tad more than the alternative, but as the alternative was about 9 separate transformers, I consider it money well spent.

I don't know if they will be able to do anything with higher frequencies, as the custom job they did for me involved standard laminations and bobbins, just custom numbers of turns.
 

Sceadwian

Banned
todd, to make it even worse, the core material itself could be any one of hundreds of various blends of solid/structured materials.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The output transformer is probably the most critical part of the entire amplifier, and will have the most effect on the sound.

This strikes me like you've broken your favourite CD (or record), so you think you'll record it yourself, playing all the instruments and doing the singing as well.
 
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