Rust removal and painting transformers

[LeapFrog]

I have a single tube amplifier, the transformer was rusty so I sanded down all the outside edges I could access
(used a file and sand paper) then I painted it with black enamel.

The transformer seems to run hot?
It didn't occur to me at the time that maybe the stack of plates could be different kinds of metal alternating??? Is that how it is made?
And that by sanding the edges of the plates to a continuous shiny metal surface I could impact the transformer's characteristics?? By creating conductivity across the plates??
Is this even a thing, also can the enamel be causing the transformer to run hotter? Do the plates need to "breathe"?
I can rest my hand on it, but barely... it is hot.

"If you are still bothered by the cosmetic aspect of rust, never scrape off the rust to the point of exposing bare metal because you will bring back those nasty eddy currents. Instead, brush off the loose particles and re-paint the area with varnish. If you want to send your transformer to Mercury, we can re-dip it in varnish and bake it for a small fee. Transformer evaluations are always no charge providing you cover the shipping costs to and from Mercury."

I don't know what kind of transformer they are talking about in that quote.
Did I damage the vintage amplifier with my vigorous sanding?
Thank You

 

[Tallman]

Laminated cores is what they are talking about. The eddy currents are dissipated as heat in the plates of the core. I don't know if this will work for your application but one company I worked for had battery chargers that put out 400 amps to charge electrical forklifts. They complained the manufacturer about heat and a buzzing sound and they sent out a technician to fix it. He got one of our arc welders and ran a weld across both sides of the transformer. That fixed it for us, but like I said I don't know if it will work for your application.

 

[LeapFrog]

Laminated cores is what they are talking about. The eddy currents are dissipated as heat in the plates of the core. I don't know if this will work for your application but one company I worked for had battery chargers that put out 400 amps to charge electrical forklifts. They complained the manufacturer about heat and a buzzing sound and they sent out a technician to fix it. He got one of our arc welders and ran a weld across both sides of the transformer. That fixed it for us, but like I said I don't know if it will work for your application.

Okay, so I have a laminated core tansformer, I am no longer concerned about the fact that I have sanded the laminations together and created a smooth surface that could be possibly conducting easily across all the laminations. &
I appreciate your story about the tech who welded the plates on either side.

My next concern is heat.
Are these type of transformers supposed to run kina-hot, and did the enamel seal off the laminations to a point where they cannot "breathe" (dissipate heat) as effectively anymore? Thereby creating more heat, possibly affecting Eddy currents?

I am imagining the laminations could somehow "breathe" easier before I started sanding down all the edges. I could use somebody's honest opinion. Am I being overly worried and paranoid?

Thank You

 

[kopcicle]

Breathe? Most high end power transformers are potted. Meaning dipped in varnish/goo and vacuum bagged or just immersed and allowed to drain excess before a light baking .
So breathe ? No , not so much.

Welding the laminations. Yup, simple fix.

Search Heathkit HA-10 choke noise . Interesting results and fixes.

Rust removal . https://www.walmart.com/ip/OSPHO-Ru...7459&wl11=online&wl12=155312117&wl13=&veh=sem
Yeah well that link was huge . Shop around because some will gouge the hell out of you for the HazMat shipping. I get mine from the local Ace Hardware.

Heat . Its rare for a transformer to run cool to the touch. Nature of the beast is to heat as it works. Now hot to the touch and you need to examine the KVA of the transformer and what you are asking of it .
[rant] The iron itself was the most expensive part of an old sweep tube amplifier when it was built. I can't think of one manufacturer in the CB market that supplied any more iron than was actually needed. In most cases the transformer was marginal, fed a doubler, just enough diode, into far more capacitor filter than needed, with curious bleed resistor values, into nearly twice the load the transformer was designed for .I have had a few and you could cook breakfast on all of them . [/rant]

After filling the house with the acrid smoke from a couple of these burn downs I got better at the engineering side of these things. I over build but not to the point of necessary excess (or weight) . I will never under spec a transformer again .

Questions ?

 

[nomadradio]

Does it get hot with no load?

What kind of load is on it?

Has a lot to do with the heat it should produce.

73

 

[LeapFrog]

Does it get hot with no load?

What kind of load is on it?

Has a lot to do with the heat it should produce.

73

It is a Wawasee JB-150 (1x 8417) If I recall correctly it was getting a little hot just letting it "idle" in standby mode or maybe just when "on"; I haven't ran the unit in over a week, my memory fails me. I can plug it in and take some type of heat measurement, but I do not have a clamp-on style ammeter at this time.

The tube is very close to the transformer (about an inch away)
I have decided to use a 2 Amp fuse, instead of the 3 Amp listed in the schematic, so far it hasn't popped so that must be a good sign!

@kopcicle How can I spec a transformer for any applications, do I use Ohm's Law?
~Edit: found some basic info here!

For 208 volt primary to 480 volt secondary, 150 degree temperature rise units are on page 5.4.

Thank You

 

[Beetle]

How can I spec a transformer for any applications, do I use Ohm's Law?
Thank You

Not exactly Ohm's Law: use power in = power out Primary voltage times primary current under load and unloaded must equal the total secondary voltage/current on each secondary winding.

 

[giboni]

Hmm. Personally I would not sand. Have a bunch of Rust Buckets.

I use this. Rust Reformer

 

[LeapFrog]

Thank You, phosphoric acid!

 

[giboni]

Hold on......Ponder first what a concentrated form of phosphoric acid can do to the Iron.

The transformer.

Remember. Inside are copper wires wound around the core. These thin wires have a

very thin layer of insulation.

Check these pics. Before & after. With Prep and Etch sold at HD.

RUST Reformer has other ingredient's. No need to even paint.

 

[Onelasttime]

I would not worry too much about some surface rust. Burnishing it with a wire wheel or brush then if you want paint it with something like POR15 or Rustomlem etc.... Banding helps with the buzz or welding but it will not eliminate it. The wire in the unit is copper and is pottered in varnish, wax, tar or epoxy so it is all a non-issue. It is likely not high silicone steel hyper-sil if it is insanely rusted. You could even just spray some clear on it.

The power supply creates a lot of heat not as much as the tube but a lot. In fact I have often thought it is idiotic to put the power-supply in the same box as the tube and tuning circuits. People always want legal limit in a small table top foot print in spite of it being dumber than dirt to do so!

You know they heat steel with electromagnetic induction passing power through coils. Anytime you deal with electromagnetic or dielectric forces transforming energy stepping up or down or doing any form of work you will always have heat. Same thing applies to mechanical transformation of energy again heat is always a product.

In fact even something simple like a transistor turning on and off one of the by products of that is heat. In fact high voltage railroad tracks bend slightly due to dielectric forces. You will not see it with the naked eye mind you. If it is not smoking it is probably fine. Have you considered using a $29 non-contact thermometer to take the temp under load with no contact?

Always good to exercise caution and use all of your senses but with out something more empirical than "it is getting hot" hard to say if it is serious or normal!

 

[LeapFrog]

I would not worry too much about some surface rust. Burnishing it with a wire wheel or brush then if you want paint it with something like POR15 or Rustomlem etc.... Banding helps with the buzz or welding but it will not eliminate it. The wire in the unit is copper and is pottered in varnish, wax, tar or epoxy so it is all a non-issue. It is likely not high silicone steel hyper-sil if it is insanely rusted. You could even just spray some clear on it.

The power supply creates a lot of heat not as much as the tube but a lot. In fact I have often thought it is idiotic to put the power-supply in the same box as the tube and tuning circuits. People always want legal limit in a small table top foot print in spite of it being dumber than dirt to do so!

You know they heat steel with electromagnetic induction passing power through coils. Anytime you deal with electromagnetic or dielectric forces transforming energy stepping up or down or doing any form of work you will always have heat. Same thing applies to mechanical transformation of energy again heat is always a product.

In fact even something simple like a transistor turning on and off one of the by products of that is heat. In fact high voltage railroad tracks bend slightly due to dielectric forces. You will not see it with the naked eye mind you. If it is not smoking it is probably fine. Have you considered using a $29 non-contact thermometer to take the temp under load with no contact?

Always good to exercise caution and use all of your senses but with out something more empirical than "it is getting hot" hard to say if it is serious or normal!

Thank you OneLastTime, yes I didn't know at the time, but the amount of heat is not an issue, just was my first amplifier that ran on a vacuum tube!

Now that I have another to compare against, I think it is A-okay and not scorching. Just gets almost hot to the touch after being on for a few hours, but nothing smells funny like varnish cooking off! But it does get warmer than I expected!

The black enamel hasn't burned off or smelled, if anything I helped it cure faster.