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?
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?
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...
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?
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
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
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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.
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.
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,
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.
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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.
Not tried it but the technique was used to improve creosote absorption in preserving timber.
Thankfully, the vacuum pump I bought to install air conditioning in my Mazda Miata (a project which never got off the ground), is absolutely functional as I tested it last night. I hooked it up to a plastic bottle, and it literally sucked all the air out of it until it was completely flat.
It's just a cheap thing which uses the venturi effect to make vacuum out of compressed air, not a real vacuum pump, but it does seem to work well enough to use.
It is no trouble to pre-heat the transformer though, I think if I'm going to do this, I want to do it once, and I want to do it right. Once the varnish cures, there will be no second chances. I like that idea, because some heat will help reduce the viscosity of the varnish at the same time as expanding the air.
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My professional experience goes 30 years back and related to space equipment. We actually had a vibration board inside the vacuum chamber (with heating) but for you it is a matter of resources I assume.
The less viscosity for a start, the better. The trick is evidently to cure in part the resin (increase of viscosity) before you return the pressure such that the resin does not have time to run out afterwards.
We used some epoxy resin with nasty warning signs on the package. It was from Emerson if I recall right. Today you have other products. I once used a two component epoxy for painting my wooden stairs. It was very liquid for a start and then hardened up to be very robust. Also that was taken off the market due to health risks.
Today, I guess a good candidate would be a polyurethane. It has to start very liquid (low viscosity) and give you 10-15 minutes before starting hardening. The end product must be pretty hard but not completely rigid because else it will just crack. Avoid fillers as they just block entrance to the small cavities.
We solely used chemical hardening under raised temperature. Air-drying, where a component evaporates, leaves me the impression of a fragile result. Before the environmental days it was the two-component stuff that just worked and could probably kill the planet.
Use a protection mask (for industrial painting) when you do such work. Amble ventilation and kids + pets far away.
Take an EI-transformer from any Japanese amplifier with an age of 30-40 years and put your nail in the resin they used. Then you know the type of shore-hardness you want.
Have fun and be careful,
The less viscosity for a start, the better. The trick is evidently to cure in part the resin (increase of viscosity) before you return the pressure such that the resin does not have time to run out afterwards.
We used some epoxy resin with nasty warning signs on the package. It was from Emerson if I recall right. Today you have other products. I once used a two component epoxy for painting my wooden stairs. It was very liquid for a start and then hardened up to be very robust. Also that was taken off the market due to health risks.
Today, I guess a good candidate would be a polyurethane. It has to start very liquid (low viscosity) and give you 10-15 minutes before starting hardening. The end product must be pretty hard but not completely rigid because else it will just crack. Avoid fillers as they just block entrance to the small cavities.
We solely used chemical hardening under raised temperature. Air-drying, where a component evaporates, leaves me the impression of a fragile result. Before the environmental days it was the two-component stuff that just worked and could probably kill the planet.
Use a protection mask (for industrial painting) when you do such work. Amble ventilation and kids + pets far away.
Take an EI-transformer from any Japanese amplifier with an age of 30-40 years and put your nail in the resin they used. Then you know the type of shore-hardness you want.
Have fun and be careful,
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This gives me plenty to think about. I will be working in the detached garage, with the door open, and I do have a good respirator to wear. Resources are definitely a concern, since this is a hobby project, and likely a one off - but the amplifiers have some value to me, I've been using them for 15 years, and I don't mind to spend a bit of money to do the job properly. I think it could also be interesting from a learning perspective, and who knows, maybe I will find other applications for the equipment.
Here's one product I am considering. It is not polyurethane, but it's reasonable priced, and available in smaller than 55 gallon drum quantities
Pedigree 12-0-12 High-Temp Varnish, translucent (1GL)-Electrowind
https://www.electro-wind.ca/media/files/elantas/datasheet/pdg-12-0-12.pdf
I'm going to keep looking on that website though, and see if there's anything more suitable.
The first compound is "water-borne" and, though I am not environmently unfriendly, sound like "what you are allowed to use today, guys". The second one sounds a bit more promising.
I do not know about the status in Canada today, but if I would seek advice by someone who makes wooden furniture for a living, he could probably tell me where to get two component polyurethane intended for wood. Or, perhaps consult someone repairing/manufacturing epoxy leisure boats. They used to know "the good stuff" as well.
I guess you are not demanding particular (high stress) insulating properties?
I do not know about the status in Canada today, but if I would seek advice by someone who makes wooden furniture for a living, he could probably tell me where to get two component polyurethane intended for wood. Or, perhaps consult someone repairing/manufacturing epoxy leisure boats. They used to know "the good stuff" as well.
I guess you are not demanding particular (high stress) insulating properties?
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It is interesting to me that you are suggesting to use a varnish which is not rated specifically for electrical applications. I was looking specifically at electrical varnishes not because I know for sure it's required, but rather because I don't know what to look for, and thought this is a cautious approach.
The "primary" insulation is still the insulation which is presently on the magnet wire. The power transformer does have a 755-0-755 volt high voltage winding, so I don't want to do something which could compromise the integrity of the existing insulation, but at the same time I can't say I know for sure it needs something better or not. Basically my intention is to fill all the air space inside the transformers with "something", to eliminate any buzzing or humming under load. How to get to that end point is what I'm still trying to figure out, but I think the advice here already has me going in the right direction.
Edit- You know, it's interesting, the website says the product I linked to is waterborne, but as soon as you click on the data sheet, it says solvent borne. I'm not sure which it is, but that's a good catch. The last thing I want to do, is introduce water into a high voltage transformer.
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Unless you use a compound with a conductive filler I cannot see it can make the insulation properties worse. You already have the basic insulation (I hope). Of course, the worst would be if the resin you add has a very aggressive dissolvant in it that would attack the old enameled wire. Ask where you buy the stuff, it is not likely because then also wood would be affected.
Yes, the existing construction is enameled wire, with layers of kraft paper in between, and some existing dried out old resin, consistent with how transformers were made at the time. There's no electrical issues with the transformers, they would have been representative of high quality products when new.
I sent an email to electro wind, asking about if the product I asked about earlier is water based, or not. I am thinking that one big advantage to a one component varnish, is I can do the four transformers in batches. With a two part product, I would either have to do them all at once, or buy a lot of extra varnish and throw it away after.
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Ordered one of these on eBay:
1.5 Gal Stainless Steel (SS) Vacuum Chamber + W-SlickVacSeal | eBay
A friend has a piston style vacuum pump I'm going to borrow. Am going to figure out how to set the chamber on to a base which vibrates.. looking forward to trying it out. I think I will start with some cheap varnish, and a transformer I don't really need.
Am going to get a used toaster oven to use for heating the transformers.
1.5 Gal Stainless Steel (SS) Vacuum Chamber + W-SlickVacSeal | eBay
A friend has a piston style vacuum pump I'm going to borrow. Am going to figure out how to set the chamber on to a base which vibrates.. looking forward to trying it out. I think I will start with some cheap varnish, and a transformer I don't really need.
Am going to get a used toaster oven to use for heating the transformers.
A very reasonable price for a vacuum chamber.
The problem will be the weight of the chamber+resin+transformer. You cannot just support it on a bass speaker. I cannot recall if we had a rotation element with an eccentricity and simply regulated the rotation speed. 30 years is a long time for such details.
Do some cheap experiments for a start to get some feeling with the procedure.
Good luck,
The problem will be the weight of the chamber+resin+transformer. You cannot just support it on a bass speaker. I cannot recall if we had a rotation element with an eccentricity and simply regulated the rotation speed. 30 years is a long time for such details.
Do some cheap experiments for a start to get some feeling with the procedure.
Good luck,
I was thinking to mount it on a resonant box made out of, say, 1/2" plywood, clamp the chamber firmly to the box, and mount a 10" speaker directly under the chamber. Then just drive the speaker to maximum excursion with a powerful amplifier.
I do like the idea of a motor though, that would be a lot easier, say use a fan motor with an eccentric weight mounted on the shaft, and power it with a dimmer switch. I can probably throw something functional together out of junk parts.
Thanks for all the advice, this is the sort of thing which makes me very happy I have the internet to fall back on!
I do like the idea of a motor though, that would be a lot easier, say use a fan motor with an eccentric weight mounted on the shaft, and power it with a dimmer switch. I can probably throw something functional together out of junk parts.
Thanks for all the advice, this is the sort of thing which makes me very happy I have the internet to fall back on!
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