How to cure buzzing chokes/transformers?

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this is how the Dynaco st70 power traffo looked like, see the wooden wedge used to ensure a tightly stacked core....
 

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I wrote to this company about obtaining a small amount, this product looks quite appealing:
http://www.crosslinktech.com/data_sheets/single_component_epoxy/CLS9310.pdf

It indeed looks good.
It is a company working with epoxies and polyurethanes. In particular polyurethanes are known to have a strong adhesion. You will need that because your primary concern is to glue the core-plates together such that they remain silent. Secondarily to fill the space in-between the windings to keep them in place. I guess you are repairing 50/60Hz items such that the dielectric properties are less important.

"Note 1" talks about fillers. It starts with "...If a filled resin,...", so I assume this to be a general note. You hardly want fillers in your resin because they tend to clog up the impregnation flow.
Fillers are very useful for embedding of circuits with really thick layers where they prevent cracking. Not suited for impregnation.

For the vibration you can eventually try both options by simply holding the bass speaker or motor with an eccentricity in your hands and feel what is the hardest to hold. The thin ply-wood support sounds like a fine idea as it is very flexible. It will make some noise.

Before impregnation, clean the items well with compressed air. After 50-60 years a lot of dust must have entered. Safety-glasses! Compressed air removes dust and eye-balls with the same enthusiasm.
 
So the response is they make product to order, and need a minimum order of 8 gallons, which have a 3 month shelf life.. not gonna work for me, unfortunately. Will keep looking for a suitable product - shame, as this one has a cure temperature of only 125C, and also, seems to have good electrical and physical properties. You are absolutely correct, strong adhesion is the highest priority. These old RCA theater amplifiers really are my favorite amplifiers, but the buzzing sound the chokes make gets in the way.

I like the idea of cleaning with compressed air, I always blow out old equipment before I bring it into the house. The old transformers also have some loose paint on the outside, I'm not entirely sure if it makes sense to just wire-brush this a bit, or use some kind of solvent. I don't want to contaminate the epoxy with residual solvent or stripper, and I also don't want to damage the coating on the laminations, so I am thinking just a quick wire brushing to get them as clean as I can before dipping.

That Dyna transformer looks pretty good! Is it original from Dynaco?
 
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I sometimes start with a brushing, using a soft painting brush, if the dust is likely to stick. I finish with the compressed air.
For the loose paint flakes, they are mainly disturbing the aesthetics and too much mechanical handling may make more damage than good. I would remove what I could get off with a dry cloth and accept it is primarily about the electrical functioning.
As you are not sure what are the initial materials used, I would use as little chemicals as possible.
 
I sometimes start with a brushing, using a soft painting brush, if the dust is likely to stick. I finish with the compressed air.
For the loose paint flakes, they are mainly disturbing the aesthetics and too much mechanical handling may make more damage than good. I would remove what I could get off with a dry cloth and accept it is primarily about the electrical functioning.
As you are not sure what are the initial materials used, I would use as little chemicals as possible.

This is very prudent advice. Function is paramount, I would way rather have ugly transformers which are silent and work perfect, than pretty ones which are compromised from a performance standpoint. I remember when I first ordered Hammond transformers, I thought they were quite ugly, all covered in thick resin. I guess I didn't appreciate at the time, now I understand this actually made them better than some of the nicely painted but not impregnated competition.
 
About a dozen years ago I tried vacuum impregnation. (I already had a lab grade vacuum pump that I had lucked into). I submerged my coils in a home made “Q-Dope”. At the time I was having hard time finding real Q-Dope so I followed a suggestion to dissolve packing peanuts (expanded polystyrene I believe) in a solvent (I used Xylene). All I can say is that it seemed to work (I don’t quite remember what coil I used this for but it was not a transformer)..In any event, I would expect an appropriate epoxy or polyurethane would have to be better than either real or clone Q-Dope.
 
1) as recommended, clean it well

2) dry it. Either in the Sun, under a spot (old style, no LED or anything modern , we want lots of infrared) or in a gas oven set to minimum and with door slightly open or an electrical oven.

3) buy a can of regular, general purpose "synthetic" wood varnish, Marine type does not hurt.
The old type which stinks for hours, seems to attract all dust in the place, remains slightly tacky for hours, the cheapest one.
Not 2 component, Polyurethane, etc.

4) put the warmed up transformer in a fitting container and slowly pour varnish to a side of it, not "on" it, you want to cover it "from below" to make it easier for air to leave.
Then let it soak for at least a couple hours or overnight.

Not as efficient as vacuum impregnation, but not far from it, you trade speed for simplicity and cost.

5) next morning you pull it by the wires, tie it to a broom handle or similar between 2 chairs and let excess drip back into the pot or can.

That general purpose varnish is not wasted, can be used on wood, furniture, whatever .
Let transformer stop dripping, even if it takes a couple hours, who´s in a hurry?

It might take 1 or 2 days for it to stop being tacky, no big deal.

You will KILL buzzing :)

EDIT: I commercially make transformers, buy specific impregnation type, both air cure and oven cure, but in a pinch wood varnish as I suggest has saved me countless times.
Only problem is that when it warms up, it stinks for the first couple days ... no big deal.
 
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+1 very good advise there...JMFahey......:checked:

i was adamant to say "wood varnish", but now that you mentioned it....:cool:
except that over here those are more expensive per liter than the electrical grade varnish being sold....

this is how i do mine....the hot manila sun raises temperatures of the traffo by as much as 50*C in summer...
 

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Looks good.

You want "old style" varnish, not "green/water based/eco friendly/low smell", its solvent should be the petroleum distillate version of turpentine (which is a vegetable extracted product), don´t know the local name but looks like "white kerosene", it´s the standard synthetic/oil pain thinner and brush cleaner.

NOT car paint type thinner either, which contains acetone and ethyl ether and will attack insulation.
You or the paint shop guy should be able to identify it with that data.

*Maybe* it´s called "mineral spirits" in English.
 
Some local home improvement warehouses include:

Lowe's Canada: Home Improvement, Appliances, Tools, Bathroom, Kitchen
www.homedepot.ca
Shop Canada’s Top Department Store Online & at 500+ Locations | Canadian Tire
Projets de rénovation, décoration et construction pour la maison | RONA

Specialty paint stores like where I found the marine varnish, include:

Varnish - BoatCraft


Specialty wood finishing:


http://www.leevalley.com/en/Wood/page.aspx?cat=1,190&p=42942

(maybe nothing useful here)


And then there's the paint stores, there might be something useful here:

https://www.cloverdalepaint.com/professionals/product-profiles/lacquers-wiping-stains

The post catalyzed varnishes above look especially interesting, but there's no info about viscosity or dielectric, as for the electrical varnish.


I think the closest to "old style" I can find above, is the marine product I linked to earlier.


Thanks everyone very much for taking the time/interest to contribute. I really want to get this right, since I don't see there being a second chance to try another product.
 
Thanks for the good links.You have products very similar to what we have here except for varnish for wooden boats. Such wooden boats are rare and expensive here.

Would include in my considerations the two following products:
Minwax Helmsman(R) 946ml Clear Spar Urethane | Lowe's Canada
Minwax Helmsman Spar Urethane | Canadian Tire
Armor Coat Exterior Spar Varnish, Gloss, 1-Gallon | Canadian Tire

Two links are the "Helmsman", one particularly for boats.
At least the Helmsman is polyurethane based which means superior adhesion and that it most likely remains flexible to some degree. Both are for outdoor use meaning sturdy and prepared for temperature variations, which you will have.

I expect the viscosity to be fine as the varnishes are else difficult to paint with.

For the electrical properties, I see little risk because you already have the insulation needed. For the dielectric properties, they are in play for high voltages and frequencies because they may add capacitance to the coils. For low frequencies (50/60Hz) and low voltages (up to 240Vac) I would expect no considerable lowering of the resonance frequency.

The advantage with a nearby warehouse is you can go there, find the can and shake it a little - does it have a viscosity like ordinary varnish?
You can read the composition and handling instructions on the can, not all Internet descriptions are elaborate. If it is a good product, you can try to find the cheapest supplier.

As you have already mentioned, find a couple of old transformers (without particular value) and test the procedure and result for a start.

I recently did some repair of old amplifier transformers. Only surface repair with a brush. I used a varnish intended for metal and based on an alkyd resin. It worked fine.
 
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PRR

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...its solvent should be the petroleum distillate version of turpentine (which is a vegetable extracted product)...*Maybe* it´s called "mineral spirits" in English.

Yes, Mineral Spirits. The cheaper fractions of petroleum less volatile than car fuel. As you say, there are stronger solvents which would be bad here.

I double-taked when you said turpentine was a vegetable. Perfectly true, except my pine trees would never fit in the salad aisle at the grocery store. But turpentine was a major reason the English colonized my area. (Masts and pine-pitch were even more valuable.)
 
I picked up a quart of the Armor Coat gloss Spar Varnish at Canadian Tire tonight. The thrift store didn't have any large sized toaster ovens I can use to dry the transformers out, so I'm going to go back in a few days.

It says it needs 12 hours to dry, so this is definitely the stuff Fahey was talking about. Since I have the vacuum chamber on the way, I'm going to wait for it to arrive before I try the varnish treatment.
 
Another vote for the varnish.

I just used some old regular varnish I had on the shelf. Leave the transformer to dry in the sun was all I did. Put the transformer in a zip lock bag, poured in the varnish, leave it sit for quite awhile, I think a couple of days in the sun so the warmth kept viscosity lower. Then take it out of the bag and leave it to dry in the sun for many days, maybe a week or more. Went from a buzzing monster to a quiet mouse.
 

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