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tbonesullivan

Amplifier Transformer Core Surface Rust

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Like all gear junkies, I'm a member of various amp groups on Facebook and elsewhere, and yesterday someone posted an amp for sale, and someone was a little down on it due to some surface rust on the output transformer core. It was a Mesa MkIIC+ with an Export Transformer, so people were worried about that, considering it's a major selling point of the amplifier.  I've never really considered thinking about it before, as most amps I have seen that are 20+ years old have some level of rust on the core, which forms when the original paint or lacquer degrades, if they had that at all. A lot of smaller transformers also have a covered core, so you can't really see it anyway.

So, I looked around, and found a Mercury Magnetics blurb about it, saying it was essentially no big deal: https://www.mercurymagnetics.com/transformer-rust-friend-or-foe/

But, this was after reading another guy say: "well it's not horrible, but it means that eventually your transformer will rust through and die".

Then I went through a bunch of Hi-Fi forums where people had various opinions, some who had tried to remedy the rust due to appearance, and others who said "just put some rustoleum over the rust and call it done.", while others were all about the WD-40.  Anyone have any thoughts on this?

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I would think that Mercury Magnetics would know a little bit more than "another guy" who thinks your transformer is going to rust through and die, like a '57 Plymouth.   Unless you are seeing rust flake off in chunks,   and you're going to be playing in rainstorms,  I doubt you have anything to worry about for at least the next 50 years or so.

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Yeah. It's only on one amp I have, which was bought used, so it probably was in a basement for a while. It's only a little bit, and the amp sounds fine, so I'm not going to mess with it.  It does seem though that over time the Electrical varnish they coat them in will start to flake off due to the heating/cooling cycles. You can see a bit of the orange varnish lifting up on the transformers in my Rivera R55:

rivera04.jpg

 

Also at this time I have noticed that the 50 Watt transformers Rivera uses are definitely significantly bigger than the ones that Mesa Uses. See.. now this makes me want to go get insulating varnish and touch up my transformers. UGH. Stupid OCD.

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Posted (edited)

I asked Chris Merren about this ( he makes top quality transformers for Neve consoles, Marshall amps, McIntosh audio gear, and is a huge vintage Marshall enthusiast )

surface rust isn't a big deal, since everything happens inside the windings & near the core. But you can use a treatment called "Mar Hide one step" that the navy used on their battleships vs rust: it actually reacts with rust to form a plastic & also seals

I used this on a '65 JTM100 power transformer about 15 years ago, it is still going strong & there has been no rust, ever since

Edited by bolero
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yeah, I had seen some suggest similar products on their transformers. I've really only got one amplifier that has any noticeable rust, my carvin x-100b. I might think about getting some of that stuff, as I also need some to use on the undercarriage of my car, and motorcycle.

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