Rusted transformers?? Are they a problem?

War_in_D

War_in_D

Well-known member
Picked up another Mesa Multi-watt yesterday, mainly to get the cabinet but got a decent deal for the entire half stack to I grabbed it all. When I went over to the seller's place to check it out I didn't really look into the back of it and there is way more rust on the transformers that I had anticipated. It was in a shop building that was particularly well lit. The guy had just moved up from Louisiana, and I guess the humidity had done a number on the trannies. I did some looking online, and the general consensus is that as long as the transformer isn't oozing anything indicating that they got really hot (melting the resin between the plates) then just leave it alone. A couple of places said that if you remove the rust it could be more detrimental than just leaving it there as it provides a bit of insulation against "eddy currents" if you expose bare metal. I've not a clue about any of this, so I'm asking the experts here.. Does that sound right?

Other than the rusted trannies, it's pretty stinking clean and sounds good but needs some power tubes. I can tell they have rode pretty hard.
 
Are both rusted equally? Usually the problem is when the OT is rusted and the PT is not. That indicates excessive heat melting plate laminations exposing raw ferrous alloy which then rusts.

If both are rusty then it’s likely a case of just not storing it correctly or salt water corrosion causing rust.

Removing the rust won’t do anything as it will just rust over again. You have to actually treat it to prevent it from reoccuring. If that’s the route you want to go, I recommend clear high temp enamel. Grab some at your nearest auto parts store. Remove the rust with 0000 steel wool, Tape off the whole chassis/end bells/remove glass/etc/etc, then coat with enamel.

Eddy currents are loops of current caught in perpetual motion around the core which interrupt the flow of flux from primary to secondary. Surface rust isn’t going to do jack fuck for that problem.
 
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Thanks! They are both rusted equally, looks like they spent their entire life outside at a seaside bar.. LOL

When you say "treat" them, do I need to try to use any rust converter type stuff on it before coating it with enamel?
 
War_in_D said:
Thanks! They are both rusted equally, looks like they spent their entire life outside at a seaside bar.. LOL

When you say "treat" them, do I need to try to use any rust converter type stuff on it before coating it with enamel?
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Clean it up and seal the plates with enamel. Won’t have a problem afterwards and it will look stock since it’s clear enamel.
 
Thanks again. I've got the chassis out right now. so it looks like I'm off to the parts store tomorrow.
 
311splawndude said:
Do you think that works better than .0000 steel wool? I've never tried foil.

Warren D - did you get this fixed. Would be neat to see before and after pics as my Rectoverb is slowly going in this direction. I can always google it too tho bro.
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Aluminum foil does work great but it gets clogged quickly and takes a lot to physically hold onto. Either will work. AF is less clean up.
 
311splawndude said:
Do you think that works better than .0000 steel wool? I've never tried foil.

Warren D - did you get this fixed. Would be neat to see before and after pics as my Rectoverb is slowly going in this direction. I can always google it too tho bro.
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Actually just brushed off the worst of it, and left it alone. I did some Google searching on it and the general consensus from places like MM are that rust on a transformer is a sign that they used good metal, and that it insulates better with the rust than without it. Most of it was on the bell housing anyway, so probably mostly cosmetic if anything.
 
311splawndude said:
Do you think that works better than .0000 steel wool? I've never tried foil.

Warren D - did you get this fixed. Would be neat to see before and after pics as my Rectoverb is slowly going in this direction. I can always google it too tho bro.
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I've used it pretty extensively over the years on hotrod and motorcycle projects to clean up rust. It's a chemical reaction so it's less elbow grease and mess, ime. I think anyone who hasn't tried it would be surprised if they did. Still recommended to coat or rust will come back fairly quick.
 
7704A said:
This sounds suspiciously like thermite.
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Guess that explains what happened to my hand
1705787911850.png
 
Transformers can be brought back with cleanings as mentioned but if you have deep pit rust in there they die typically with enough cycles
 
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