Rewinding a transformer......

[dread1]

Hello,
I have a 69 50 watt marshall transformer that is in need of rewiring.Has anybody had Mercury Magnetics rewind a transformer for them, or any other company? If so, what were the results? Is this really possible?

[mark norwine]

I'll catch hell for this, but I worked at a transformer manufacturing facility for 6 years:

With this size transformer, there's no such thing as a "re-wind".

1.) remove the bells. They can be reused.

2.) the lams get cut off with a bandsaw because they're either welded or glued (or just plain rusted) together. Can't re-use those!

3.) the 10 cent bobbin (if bobbin wound) or the former (if paper) is "chucked"...i.e. mounted on a freely-rotating arbor.

4.) the wire......miles of it......thin & intertwined, is pulled off. It is virtually impossible to salvage it, and even if you could get it off in one continuous length, you'd never get it back on. Not happening. I call BS to anyone who says otherwise. It goes out for recycling. And remember: it's bad to begin with! That's why you're having it "re-wound" in the first place.

After disassembly, what are you left with? 75 cent end bells & a 10 cent bobbin.

No, folks, there's no such thing as a "re-wind". There's only "Make a new transformer using old end-bells"

[jay42]

2.) the lams get cut off with a bandsaw because they're either welded or glued (or just plain rusted) together. Can't re-use those!I can't speak to a 40 year old british piece, but I've taken a Fender PT apart just for fun. I only destroyed the outside laminations.

[mark norwine]

But did you comprimise the coating on the others? Not even a little? Maybe only a wee bit on the edges?

No right-minded transformer manufacturer would re-use lams for just that reason. Harm the coating & eddy currents can occur.

[dread1]

When I called Mercury Magnets I spoke with a guy for a half hour on how they do it. He said that it takes about three months for the whole process.They soak the tranny and get the varnish off. Then the unwind, keeping notes on every wind , and then they rewind it exactly the way it was unwound. Just sounds too good to be true.

[jay42]

But did you comprimise the coating on the others? Not even a little? Maybe only a wee bit on the edges?Good question. They're all sitting in a box somewhere...I mean to give them the heave-ho next time I see them. What's the coating made of - lacquer?

[Nolatone Ampworks]

When I called Mercury Magnets I spoke with a guy for a half hour on how they do it. He said that it takes about three months for the whole process.They soak the tranny and get the varnish off. Then the unwind, keeping notes on every wind , and then they rewind it exactly the way it was unwound. Just sounds too good to be true.

Seems crazy that they could document every single wind during the unwind!

That said, Mercury Magnetics know their stuff and have cloned a TON of classic trannys, so I'd look to them over most others for this sort of thing.

[mark norwine]

He said that it takes about three months for the whole process.They soak the tranny and get the varnish off. Then the unwind, keeping notes on every wind , and then they rewind it exactly the way it was unwound. Just sounds too good to be true.


Performing an exacting autopsy to obtain the design specs......sure, this makes sense.

But would you even want them to re-use the old wire? It's absurd.

I would hope that MM would have by now already done a "reverse engineering study" (that's what it's called) on a 50W Marshall transformer and would already know the specs. As such, they should be able to sell you a replacement with no screwing around whatsoever.

I could see them, for an up-charge, re-installing your old end bells....if that's important to you.

But a "3 month re-wind". I'm calling BS on that......

[dread1]

The guy from MMag I was talking to said that they do use new wire.
Believe me, I'm very skeptical myself. I have it in a box with their address on it, but I've yet to send it. I wish I could find someone selling a 50 watt drake out of a 69 marshall but that would probably be impossible.

[dread1]

As for the three month turn around, he said that was for soaking and getting all of the varnish off.

[jay42]

I'm no collector, so I would think in terms of getting it back up running and sounding as good, or better than ever. What is the difference in value if the amp appears to have the original iron, vs. having one of the transformers replaced?

btw, you didn't say which transformer. I'd be less concerned about a PT, but what do I know?

[dread1]

It's the output transformer that's bad. 784-139

[Nolatone Ampworks]

The guy from MMag I was talking to said that they do use new wire.
Believe me, I'm very skeptical myself. I have it in a box with their address on it, but I've yet to send it. I wish I could find someone selling a 50 watt drake out of a 69 marshall but that would probably be impossible.

You should be fine sending it to Mercury. They are not in the business of being schiesters.

The long time soak time makes sense enough. Many many folks have trusted them and I personally wouldn't hesitate to have them do the work they describe.

[WaltC]

The MM re-wind process tends to be more expensive than just buying a Tone Clone reproduction of the original tranny and I doubt that the end result would justify the time and expense. I'd get a new one from MM and if you're concerned about the appearance slap the old end bells on the new one (or send them to MM and have them put them on).

My 2 cents.

[jay42]

It's the output transformer that's bad. 784-139Marstrans carries that, but it look like he's out of stock. You should email Mr. Wallace.
http://marstran.com/InStock.htm

[mark norwine]

But what could MM hope to learn from dissecting *your* OT? Haven't they already reverse engineered a 50W Marshall OT?

- If they have, there should be zero need to "do it again" on yours.
- If they haven't, then how did they design their existing product offerings?

I'm just sayin'...

[johnny_duke]

+1 on Marstran. I would use them over MM any day. Mr. Wallace knows his stuff. I have heard his tranny's in operation and they have accounted for some of the sweetest jtm 45 + 50 watt plexis that i have ever heard.

[dread1]

Mark you're right. The things that you're saying are all the things that I've been thinking. The reason I'm looking for an original drake is that my father bought this, along with an 8x10 cabinet that I still have. Other than the trans being changed it's bone stock. Maybe I'm better off looking for a 69 basket case that had every mod under the sun but kept the original trannies. I have an orange OR80 M that is also bone stock in black tolex that I'd be willing to trade.