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DIY transformer and two-component epoxy adhesive

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This question is not really tube related, but probably most people that make their own transformers are building tube amplifiers, and probably found out how to solve it.

I just added a pair of bells to a power transformer I built last month.
Worked great, but there was a very audible buzz. With the bells in place, it is reduced, but not eliminated.

Would it be a good idea to use some two-components epoxy adehesive to apply externally? Only a small quantity is needed, and it should help reducing buzz. :yes:

The main problem I see is that it could be almost impossible to take the laminations appart if the transformer, for some reason, fails.

How do you finish your power transformers?
 
No do not glue them on.

Try thin pieces of cardboard or plastic to make spaces.
Corn Flake packets or ice cream containers like this are easy to try.
If the chassis is steel, you may also want to add soft washers under the transformer mountings.
Just make sure you ground the end bells and transformer core too.
 

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Sorry I might have not understood your original post.
Is it the transformer 'buzzing', without the end bells?
Or are the end bells buzzing when you mount them on the transformer?
A picture might help.

The red shims are plastic, by the way, and it stops the end bell buzzing on the transformer core.
 
Buzzing without bells. Quite a lot.
Then, with bells, it is very much reduced, but still there.

By the way, one secondary winding uses heavy gauge (1.5mm wire), very stiff wire, so there's space between wires. I used polyester adhesive film over it, before final isolation, to stop them from vibrating.

Also, I designed the transformer to not have a high B (~1.2T). Uses GOSS laminations.
 
Are you using half wave rectifier? Some dc voltage will build up in a half wave rect circuits and may cause buzz.
Arent you supposed to vacuum impregnate with some kind of lacquer to hold things together? Epoxy can work and since its not a ferrite core its unlikely to harm the xfrmr.
 
What harm would you expect from epoxy to a ferrite core?
Best regards!

Magnetostriction. Steel laminates can handle it, but ferrite is too brittle. The recommended fix is first a thin coat of elastic material, silicon or someting similar, before potting into something as hard as epoxy.
The magnetostriction causes very minute vibrations so just a thin layer of an elastic coat is enough.

This is at least the recommendations, certainly ferrites have been potted without this and lived happy, but if your magnetics behaves wierdly (unexplained loss of inductance etc) it may be due to the potting compound restricting free movement of the core. Worsed case it may crack.
 
I told my better half our refrigerator was broke...it wasnt...and removed the compressor and use that as a vacuum pump. Lots of diy vacuum pumps for composite layups out there (google). Still havent got the little buckets so I can vacuum impregnate transformers, but thats the plan when I ever get the time...
 
This question is not really tube related, but probably most people that make their own transformers are building tube amplifiers, and probably found out how to solve it.

I just added a pair of bells to a power transformer I built last month.
Worked great, but there was a very audible buzz. With the bells in place, it is reduced, but not eliminated.

Would it be a good idea to use some two-components epoxy adehesive to apply externally? Only a small quantity is needed, and it should help reducing buzz. :yes:

The main problem I see is that it could be almost impossible to take the laminations appart if the transformer, for some reason, fails.

How do you finish your power transformers?


Buzz in transformers is mainly due to the magnetic field, in the core is called magnetostriction, but in the windings there is also a force between wires and it causes buzz too.

The cure for both is the same, when I wind my own transformers I use long pot life epoxy, wet windings, maybe in your case is too late.

SemperFi gave you a good compromise solution with vacuum impregnation, use low viscosity transformer varnish, unlike wet winding, it never reaches all interstices, but it is better than nothing.

A well build transformer does not buzz, you need a stethoscope to hear any noise, the last step is potting the transformer with tar, or a boutique potting compound, silicone, epoxy, etc.

A well calculated/build transformer does not need to be rewinded.
 
Wet winding, vacuum impregnation,... all of this makes reopening and rewinding the transformer almost impossible, doesn't it?
So, why not use epoxy to glue the laminations as I proposed? Should be better than npthing. It just requires a brush and some easy to get two component epoxy glue.
I can't do vacuum impregnation, nor play with dangerous products.

Bee wax seems to me even better, but max temperature is just 65ºC. Maybe easy to get in summer time.
 
Oh sure epoxy may work well. (I said that in my first posting). But if you plan to disassemble it perhaps sikaflex or something similar is better? (Easier to remove I think).

If you want the epoxy to get further into the windings/laminations you should heat the transformer a little since warmth makes epoxy thinner and runnier. But then it'd be difficult to take it apart I think.
edit: In case you didnt know: Epoxy with long cure time is stronger than quick cure types.
 
I didn't know sikaflex, but it looks like a good alternative. It is flexible, able to fill gaps, not agressive and does not withstand alcohol (so maybe can be removed with some effort).

Being able to dissasemble the transformer is a plus, not only for repairing or modifications, but to reuse the laminations in the future.

An OPT is much harder and time consuming to wind. If it buzzs slightly is OK, don't you think? When that is happening, music is always at a much higher volume. I'd rather not glue the laminations. I'll try to use better bolting/fixing and use that cardboard/plastic interface Alan4411 recommended.

But a power transformer buzzing is annoying, because you're always hearing it. Also much easier to wind, and probably a better candidate to reuse laminations. I will try this sikaflex of even epoxi on it, and see if the buzz goes aways.

Also, it might be a good idea to unwind the 6.3V filament winding, and redo it.
It now uses a thick 1.4 mm wire (no CT). Very stiff. Turns are not in perfect contant at all. There's quite lot of air gap between them. That could be a source of buzz, don't you think?
Now I have 1 mm wire, and winding a pair of this wire, using CT, would do the job, and probably make tighter winding.

Does it make sense?
 
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