Cleaning Power Transformer Bell Out Of Strange Dirt

[sarakisof]

Hello everyone, i found a Farfisa Compact organ (uses 2xECC83s for spring rvrb and preamp) that needs recap and some electronics troubleshoot. But before going so, i want to clean the PT first. I opened it and found this situation inside. The previous owner was a painter and seems something like a paint or similar was spilled because i found some paint stains on the top cover above the PT too. It is a weird material though, like an old sticky dried powder dirt. Like wall plaster or smthng. And a bit rusty. Found that the long screw that holds the two bells together and gets inside the laminations hole, has also some of that white plaster stuck. Do you thing it could damage the laminations inside, as it is passes and get screwed through them? The organ plays perfect in terms of PT and voltages are all fine.

Mostly i wonder how i can get this plaster dirt out of the bell, as you can see in the pic is like a mess. I don't want to unsolder PT so to extract bells and do a total job.
What do you guys would do if you were in my place. It doesn't affect smthng obviously, but you know, i d like to clean it a bit. Maybe cover top chassis and try brass wire brush or sandpaper and then paint clear with clear rustoleum varnish as long as the laminations too?

[GibsonGM]

It really looks like a drink spill, to my eye.  Not a paint substance (I'm a painter...), tho it could certainly be joint compound/plaster.  It could be anything! lol     I'd remove what I easily could...wouldn't dig too much into the trafo guts, not at all.   

Just, a toothbrush (nylon etc - non metallic!), maybe evaporative solvent on a rag, just get it off the bell.   Water & rag alone would clean it if it's joint compound. And I'd leave it at that, wouldn't introduce anything new like poly.    Use rags to keep the gunk out of the rest of it as you work, vacuum it up, then blow it out before power-up...

Just my 2 cents!  Nice rig.

[sarakisof]

Nice input, yeap i ve thought of all those too. I will try with a rag and isopropyl alcohol first, but from my experience isopropyl alcohol doesn't clean dirt so i maybe try some baking soda first or warm water green soap.

[GibsonGM]

IMO, you'd want to use a DAMP (not WET or dripping!) rag....then allow it to FULLY dry, of course     Even apply a hair dryer....you know the routine...

[ElectricDruid]

IMO, you'd want to use a DAMP (not WET or dripping!) rag....

...and make sure the caps are discharged at that!

[antonis]

I just wonder if it's a spill of battery leakage.. 
(in such a case, use medium copper brush & vaccum hood..)

[tubegeek]

Just a reminder - you don't necessarily want to clean all the rust off of a power transformer. The laminations are intentionally oxidized a bit to insulate them from each other and enthusiastic cleaning can introduce a short between them. This will increase eddy currents/reduce efficiency. Definitely a small effect to be sure but something to know before attacking.

What I'd do: wire brush the part of the bell that's completely outside the laminations (after borrowing Antonis' vacuum hood perhaps?) and avoid the lamination edges as much as possible.

There's a spray-can product that is meant for converting rusty metal to a paintable surface - it may be useful in this situation, I'm not sure.

Then cry cry cry now.

[antonis]

(after borrowing Antonis' vacuum hood perhaps?)

A bludged vacuum hood should be a non-negotiable spousal casus belli..!! 

[duck_arse]

(after borrowing Antonis' vacuum hood perhaps?)

.... bludged .....

sometimes you surprise me, antonis. also - transformer bells, carry on.

[sarakisof]

haha thanks guys. So i managed to remove the white material mess, it can be dissolutted and be removed with a bit hard proccess, but it had left a brown spot in underneath - probably rust from the material - that it is hard to remove. I will try though.

Also, something related, antonis and others, please have a look at this thread too: https://www.diystompboxes.com/smfforum/index.php?topic=123852.0

Most people suggest the product Fertan or any similar Rust Converter based on tannic acid, not phosphoric.
What do you think of using AmbroSol Rust Converter instead of Fertan? Talked with local dealer and told me it has no "etching/corroding warning", only the usual "danger warning". He also compared it with another can of Rust Remover and told me it has both "danger and corroding/etching warning" sign.

https://www.ambro-sol.com/wp-content/uploads//I260_EN_rev.0.pdf

[sarakisof]

And smthng more: all people mention the "appropriate" common Rustoleum for painting/coating their transfos, but heh, which one is the "appropriate" for this use? Rustoleum produces a generous number of products out there.

[GibsonGM]

I'd leave it alone.  Just my impression...thing is vintage, it's expected to have seen some use, and have some wear.  I wouldn't paint it.  I don't think it'll go thru any inspection...   

If I did paint it, I'd get a small bottle of Testor's model paint, silver, and just do that end after you clean it up.   But I wouldn't, so that's moot 

I think they mean simple "Rustoleum" spray paint.  Original...basic....nothin' fancy.  If you go to the trouble, probably should prime it first, too.  Mask everything.   I'd leave it alone tho, let its age show.

[sarakisof]

yeap i will apply rust converter first and then rustoleum. So you think smtgng simple like that woyuld be ok right?

[sarakisof]

Also look at the specs from datasheet of the AmbroSol product i m going to buy. It says "Temperature of exercise +5°C / + 75°C"

https://www.ambro-sol.com/wp-content/uploads//I260_EN_rev.0.pdf

Do you think 75°C is OK for transformer use?

[GibsonGM]

Well - in the picture, that's just clear coat.  It has no color! Only for protection as a top coat.   

I truly believe if you simply clean the bell off, and leave it alone, it will be fine!   It is a vintage piece - painting things reduces their value, EVEN if they are a little bit scarred by their 'life'.  Nobody will mind if it is not perfect!  If you do this incorrectly, you could damage it, cause it to short out and so on...ruining it!

To properly do this, you should remove the trafo from the enclosure so you can access all of it.  I don't think you should get into that.   You would need to disconnect it and that is work that seems unnecessary. 

Can you post a pic of it now that you have cleaned it off?

[Rob Strand]

I truly believe if you simply clean the bell off, and leave it alone, it will be fine!   It is a vintage piece - painting things reduces their value, EVEN if they are a little bit scarred by their 'life'.  Nobody will mind if it is not perfect!  If you do this incorrectly, you could damage it, cause it to short out and so on...ruining it!

Agreed.   There a lot of opportunity to make things look worse or even damage the transformer. 

There's guys out there that pull stuff apart, re-plate metals, and the final job looks like a million dollars.  The thing is those guys have done it all before, have had many fails, and have learnt from their mistakes.   I guess you have to ask yourself is it worth the risk of failure for a one-off.

To me it doesn't look like rust.  It looks like something has attacked the outer plating.   My guess is it's zinc and the white stuff is zinc oxide (doesn't look like cadmium plating from that era.)

[sarakisof]

It was a hard day today. I fully unsoldered it and disconnected it from chassis. Things were a bit bad there. When i unscrewed the long screws which hold laminations together the two "I"s from both side edges landed to the floor. All the other laminations seem pretty solid as they should be. So i started searching and found old videos i ve been watching in the past for glueing laminations. I saw again this video from D-lab etc etc
https://youtu.be/dtOwewfqucI
In meanwile i managed to clean all that rusty stuff out from the bell and the power enclosure chassis. Dremel wire brush could not do the job perfect, so i dipped those metals into Hydrochloric Acid for 2 minutes and job was done totally. The material was immediately disolutted. Seemed it was spilled battery leakage, as some areas and a ground bare wire had been corroded getting that "blue-green corroded salt".
Now i will Zinc plate them and see how it goes.
I was out all day searching for rust converter (non abrasive-nin phosphoric acid, but tannic acid based) , varnishes, clear coats, oil based wood paint etc but it is really hard to find those dedicated products in my area. You can only find simple acrylic varnish, strong rust removers and wood varnish water based 

So i will wait and ordered Fertan rust converter, a wood varnish oil based and rastoleum black.
Here is why.
I am planning to convert first the remaining rust from laminations, as you can see there is rust on top lamination. I want the Fertan for other transformers i have too, that have some "grey" little areas (black coat has been slightly gone off in some little areas).
Then i will glue the two "I" laminations with oil based wood varnish like in the video. I found a simple one and another that contains a bit wax. Do you think this with wax would be better?

Finally, i will apply rustoleum black paint to laminations to look like new. You will ask "why don't get an oil based wood paint black"? That's because i want to get a spray can, as i told you above i have some other transfos that i want to do a similar job, but without disconnecting them from chassis. I will cover chassis and spray them.

So rust converter(tannic), wood oil varnish to glue the two "I"s and rustoleum black paint.

Tell me what you think of.

[GibsonGM]

It looks very good.  As I said...it looks good enough for me.  (ha ha!).

If you want to paint, Rustoleum is basically oil-based.  It is close enough for your purposes.  They do add other things to make it into an aerosol, but that's probably not an issue here.   

[sarakisof]

Is it OK to use simple water based wood varnish instead of oil based PRR suggests to glue the two "I" laminations ?

https://youtu.be/dtOwewfqucI

[sarakisof]

After a loong but beautiful research journey i managed to do it guys 
As you know from previous posts i had already get all the dirt and rust (battery leakage/white strange material) off from the bell and upper chassis. After that i just coated them using 3 layers of simple acrylic metal spray varnish.

About the two de-attached laminations now, after many hours of reading, thinking and asking many people, i finally talked with a guy that makes his own tube amps and transfos from scratch. Being experienced in coils, he suggested me to call a company that sells raw materials for making transformers to customers and large companies. Coils, motors, laminations, varnishes and all that kind of stuff. The engineer guy there was kind enough saying to avoid any common wood varnishes and told me to go straight for Electrical Insulated Varnish, Polyester based. You know, industrial pro stuff like Dolph's AC-43 Varnish for insulatin and potting transfos and coils.

http://www.sinadinos.gr/pdf/ALBESIANO%20AC-43%20ing.pdf

He indroduced me immediatelly to co-operate company that repairs and makes transformers, coils and motors here in my town, i went there with an empty can and in 5 minutes the guys there offered me about 1/2 litre local Clear Air Drying Electrical Insulated Varnish for free ! The varnish is called "Elektrotek 428" and i think it's the local equivalent of AC-43. They use them in large quantities so when i went there handling two small laminations they laughted 

https://www.sinadinos.gr/pdf/Electrotek_428_en.pdf

As an answer to my question about "if this will be OK for audio transformers etc." i wa told that it would not be a problem even if i would give a bath to the whole transfo into the liquid, that's what they use for potting.

So i went home, glued the two laminations with it clamped for 12 hours,  then applied another two layers of it to the whole outside laminations and let dry for about two days. The transfo is sealed like never before, having covered any "bare lam areas etc", it is a insulated tank 

The "bad" thing is that i cannot get my hands in it any time in future as it is almost impossible to deassemble the lams anymore. I don't know if it is "bad" but i don't see any reason of doing this, even if there is some small ammount of rust already inside laminations that i cannot see, i mean i cannot do smthng for that (well except for with Fertan that it is said to can acces into lams and convert the rust anyway), this rust could maybe reach the core someday, i couldn't do many things for thisanyway. I don't know if the lams must "breath", but i don't think so, as that's the way they do it from factory, i mean, they seal them right?

In the end of the day, i re-assembled the whole thing back, bells, wires everything, soldered back to chassis underneath, fired it up and all work GREAT ! 

Measured power voltages, all perfect, i got 274-275 V. at the first filter cap and 229-230 V. in the second !
Multimeter always moving between "274 and 275" , "229 and 230", it never gets stabilised at "275" or "230", but i guess this 1 V. isn't a big deal right?
Was measuring about half an hour and exactly the same steady numbers.




What do u think guys ?