rusty transformers

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by smolder, Feb 27, 2012.

  1. smolder

    smolder Gold Supporting Member

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    search wasn't very helpful... so does it make any sense to paint rusty transformers with rustoleum? Not just for looks but to stop additional rust?
     
  2. trobbins

    trobbins Member

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    Imho, if you're in a humid environment that enjoys rusting any bare steel part, then yes by all means follow any stop-rust products instructions to halt further rusting. Transformer cores can get warm, or even tolerably hot, so I'd suggest something like an automotive type product that gives confidence it was designed for higher temperature operation - if you know that your transformer is of the warmer variety ;-)
     
  3. efnikbug

    efnikbug Member

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    I believe I've read Gerald Weber say that painting rusty transformers is recommended. It's when he says to toss the overly-rusted ones that seems to open a can of worms.
     
  4. wyatt

    wyatt Member

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  5. smolder

    smolder Gold Supporting Member

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    thanks guys... I've been told NOT to try and remove the rust that is already there, but wasn't sure about the paint... I'm a very light coat painter.
     
  6. Mrmarshallhead

    Mrmarshallhead Member

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    I neither paint nor toss them, I just give them a light rub down with a micro fibre cloth, no chemicals or anything, just the dry cloth. It should get rid of the orange iron oxide which is powdery and leave the trannies original but looking better.
     
  7. Gnarlly

    Gnarlly Member

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    You may want to try a varnish instead. Try Googling "transformer varnish."
     
  8. teemuk

    teemuk Member

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    It's typical MM technobabble. Basically, almost BS but with some hint of truth in it. Keep in mind, it's not a peer-reviewed technical article, rather a thinly-veiled advertisement of MM.

    Yes, rust is a good insulator, hence a super thin oxide film layer makes a perfect insulator for transistor laminations. And there it stops. Rust itself has extremely weak magnetic properties so letting the laminations rust too much will actually ruin the transformer, or at least severely weaken it. You don't want those things to rust or corrode. There is tons of literature written about transformers that focuses on techniques of preventing rust and corrosion. You don't see power supply companies deliberately rusting those giant transformers you see here and there to make them run more efficiently... You'd think they try to save a buck or two if the "rust makes the transformers more efficient" -claim had even slightest truth to it.

    Yeah... what do MM exactly claim in the article. Well, they run a SINGLE test and get a 240mW difference in power dissipation of two transformers. Had they run two completely new transformers side to side they still might have arrived to similar results due to overall part variance. And 240mW is practically negligible amount in power transformers handling several watts of power. WOW! I better go on to dip all my transformers into salt water to achieve such a great performance boost!

    Shame on folks who can't read through the lines and actually end up buying all this #!#ยค%.

    No, a little surface rust does no exceptional harm, and usually trying to remove it improperly or covering the rust with paint that happens to be conductive - resulting into shorting the laminations - has actually far worse effects than a little surface rust. Add to the insult, the same MM article that teaches about magnificient wonders of rust also advises to sand off rust, which is like the last thing you should do to a transformer since it's a good recipe to short laminations and have eddy currents skyrocket. Kiss goodbye to that transformer. So much for the credibility, if there ever was any.
     
    Last edited: Feb 27, 2012
  9. Jerry Glass

    Jerry Glass Member

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    This is what I routinely do since I live in the rust belt...

    I brush a light coat of transmission fluid on the laminations and leave it at that. I don't remove any rust. I have used rustoleum in certain cases (heavy rust) but as a rule, I prefer to not put that much time into it as most of the amps I see have some degree of rust on their transformers.
     
  10. trobbins

    trobbins Member

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    If you're in a humid warm environment then the rust will continue to eat away - that's what rust does in the right environment. Often one comes across a surface rusted transformer and puts it in a new environment which has benign humidity and temperature - it is then not as issue if you remove or retain the original orange 'patina'.

    As for shorting laminations to cause some noticeable effect, I'd be guessing you'd have to be using silver laden paint!
     
  11. David Robrecht

    David Robrecht Blue Fire Silver Supporting Member

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    This! I've done this many times. Just brush of the loose rust and spray on the transformer varnish.
    Dave
     
  12. Baxtercat

    Baxtercat Member

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    As said, don't sand, scratch, or wire-brush the rust. Just wipe down and respray.
     
  13. Ben S.

    Ben S. Member

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    I have brushed the lams with a brass brush while blowing the dust off with compressed air. When finished with as much as I can get off I spray them with this: http://www.amazon.com/Mar-Hyde-One-Step-Converter-Primer-aerosol/dp/B0009LPJ0Q
    Which turns the rust parts black and they make the transformers look pretty nice.

    Here is a set that I did last year:

    [​IMG]

    I also sand blasted the bells and painted them with engine block primer and cured them, then painted them with high temperature auto paint and cured them so they would stand up to the heat.
     
  14. donnyjaguar

    donnyjaguar Member

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    What circuit did you use on the Dynaco, Ben? I see it has a pair of smaller tubes now.
     
  15. donnyjaguar

    donnyjaguar Member

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    Haha! Yeah, that's my take on it. Guessing the turns inside the transformer are corroded and have higher resistance. Thus the current is lower. Its a useless test because you can't determine the efficiency with no load on the secondaries. I think they did this because secondaries were completely whipped.
     

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