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How to cure buzzing chokes/transformers?
How to cure buzzing chokes/transformers?
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Old 27th August 2018, 11:17 PM   #1
maxhifi is offline maxhifi  Canada
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Default How to cure buzzing chokes/transformers?

I have some vintage iron which buzzes, and I would like to fix this issue. I've done some reading on the topic, and also received some practical advice. Some options are.

1. Spray on an alkyd conformal coating, getting it deep into the windings. I bought a can made by MG Chemicals, but I'm a bit nervous to use it, because I'm concerned that if I do, and it doesn't work, then other methods will no longer be accessible.

2. Paint on a thinned epoxy of some sort... hard to find electrical epoxies, but this seems to be another method.

3. Vacuum impregnation of said epoxy. Either by a motor rewind shop, or buy a vacuum chamber and pump, and do it at home. Need to learn more about how to do this.

Anyone on the forum have experience with coating transformers? Am I over-thinking this?
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Old 27th August 2018, 11:30 PM   #2
TonyTecson is offline TonyTecson  Philippines
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How to cure buzzing chokes/transformers?
1. tighten the bolts and nuts.
2. if this do not work, remove the endbels and, shim the laminations against the bobbin using a wooden wedge made from popsicle sticks..
3. dunk the whole thing into a vat of electrical grade polyurethane varnish, lift and let drip then dunk again for the times...
4. let the thing dry in a drying oven, reinstall the end bells a bolts and nuts..


i have encountered endbell vibrating as well, my fix was to put epoxy mix of about 4 to 6mm thick, this will damp the end bell covers...just ensure you have enough space for epoxy on the end bells...

hope this helps...
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Old 27th August 2018, 11:37 PM   #3
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by TonyTecson View Post
1. tighten the bolts and nuts.
2. if this do not work, remove the endbels and, shim the laminations against the bobbin using a wooden wedge made from popsicle sticks..
3. dunk the whole thing into a vat of electrical grade polyurethane varnish, lift and let drip then dunk again for the times...
4. let the thing dry in a drying oven, reinstall the end bells a bolts and nuts..


i have encountered endbell vibrating as well, my fix was to put epoxy mix of about 4 to 6mm thick, this will damp the end bell covers...just ensure you have enough space for epoxy on the end bells...

hope this helps...
Thank you for the input, and sharing experience.

Steps 1 and 2 are already done, and there was a minor improvement, but I need something a bit more invasive.

What specific product do you suggest for the poly varnish?
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Old 27th August 2018, 11:41 PM   #4
TonyTecson is offline TonyTecson  Philippines
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How to cure buzzing chokes/transformers?
i do not know what is available in your place, but over here i use the clear, air drying electrical grade varnish...

the thing is to be able to dip the whole thing into a vat of varnish...
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Old 28th August 2018, 04:08 PM   #5
maxhifi is offline maxhifi  Canada
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I remembered that some years ago, I bought an air operated vacuum pump at harbour freight. The cheap kind which works on the venturi principal. Anyway, I never thought it would actually work well, but I tried it, and it can completely suck the air out of a plastic bottle, for example.

I'm going to get a soup pot, at a thrift shop, and make a vacuum chamber large enough for my largest transformer. I have found electrical varnish online, but there's so many types

-air dry.
-catalyst activated
-heat cure

The research I have done says air dry will never dry properly once it's inside the transformer windings. It is sure the easiest to find in small quantities though, and doesn't involve rigging up a special oven.

The heat cured type needs 150C for four hours, and I'm slightly concerned this can harm the 60 year old transformers I'm trying to help. Maybe it's worry about nothing though. The catalyst activated type seems tough to find in small quantities.

This website seems to have many options, but is very hard to navigate.

Electrowind - Your Source for Motor and Transformer Parts & Fabrication

Last edited by maxhifi; 28th August 2018 at 04:34 PM.
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Old 28th August 2018, 04:34 PM   #6
dtossan is offline dtossan  Canada
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Default DC Blocker

Transformer buzz can be due to deteriorations/looseness in the laminations.
Or it could also be due to the presence of tiny amounts of DC in your mains supply, which is not uncommon at all due to many reasons in your neighbourhood power usage.

If the 2nd, you may wish to consider a DC Blocker.
You can check out these for ideas:
Mains DC and Transformers
DC Blocker Trap Filter – Assembled in Case | ATL Audio Ltd.
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Old 28th August 2018, 05:49 PM   #7
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by dtossan View Post
Transformer buzz can be due to deteriorations/looseness in the laminations.
Or it could also be due to the presence of tiny amounts of DC in your mains supply, which is not uncommon at all due to many reasons in your neighbourhood power usage.

If the 2nd, you may wish to consider a DC Blocker.
You can check out these for ideas:
Mains DC and Transformers
DC Blocker Trap Filter Assembled in Case | ATL Audio Ltd.
The amplifiers in question are RCA MI-12188A theater amps, from the early 1950s. The iron which is buzzing the worst, are the filter chokes. The power supply is a choke input power supply, which has a 15H choke directly off the rectifier, and it idles at about 230mADC. This is a demanding application for a choke, and after so many years, the large magnetostriction force, plus the old varnish are enough that they produce audible buzz.

I'm not sure if they were ever quiet, I wasn't there 65 years ago when the amps were new - but if they did, it wouldn't have been an issue, as the noise would have been completely swamped out by the noise of a movie projector. In a hi-fi application though, it's definitely audible.

The secondary issue, is that under full power testing, the power transformers also make some noise. I would probably leave this alone, but if I am buying a gallon of varnish and setting up a vacuum chamber, I may as well do everything.

I repair a lot of amplifiers, and it's common for transformers to grunt or hum a bit during a full power test, but for the most part transformers operate silently at my house, so I'm not too concerned that DC on the line is an issue.

One reason I am leaning toward impregnation as the solution, is if I cup my hand over the top of the choke, and block the interface between E and I, I can reduce the noise substantially - same thing for if I squeeze the end bells in. I was thinking at first that a surface coating of varnish would cure the issue, but I also think that if I did this, it would block any future attempt to impregnate the core.
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Old 28th August 2018, 07:11 PM   #8
FauxFrench is offline FauxFrench  France
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The vacuum impregnation is the best. Be generous with the varnish. If it is too difficult with the vacuum, you may lower the items in the varnish and put the container on a vibrating support. If you vary the vibration frequency you may hit a resonance frequency where small air-bubbles are released. The wetting under vibration is improved as the surface tension of the varnish is reduced.
Good luck,
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Old 28th August 2018, 07:24 PM   #9
maxhifi is offline maxhifi  Canada
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Quote:
Originally Posted by FauxFrench View Post
The vacuum impregnation is the best. Be generous with the varnish. If it is too difficult with the vacuum, you may lower the items in the varnish and put the container on a vibrating support. If you vary the vibration frequency you may hit a resonance frequency where small air-bubbles are released. The wetting under vibration is improved as the surface tension of the varnish is reduced.
Good luck,
Thank you for this response. Since you have experience with this, I will ask some specific questions about the parts which are giving me the most trouble.

What sort of varnish do you use? Air dry, or bake to dry? Does baking an old transformer have any risk associated with it, in terms of damaging existing insulation? I've noticed varnish comes in almost a bewildering variety of ratings, viscosities, etc, and I want to be sure to use the correct product.

Further to this, if I combine vacuum with vibration, maybe it's even better? It would be really easy to attach say an old 10" subwoofer to the bottom of the container, and drive it with a power amplifier and audio oscillator.

Last edited by maxhifi; 28th August 2018 at 07:27 PM.
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Old 28th August 2018, 07:36 PM   #10
russc is offline russc  England
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Warming the pot containing the varnish & Iron would expand the air and some would escape. Or even warming the Iron before dunking. Then allowing to cool while still dunked the varnish would replace the expanded air. May be useful if a vacuum is not readily available.
Not tried it but the technique was used to improve creosote absorption in preserving timber.
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