If you were looking top down at a typical "classic" transformer or a choke... Is the emitted magnetic flux energy greatest out the sides with the winding or the sides with the laminations? Also I have some ferrous metal transformer covers on order, does a ferrous amp cover help much with flux or are they just pretty?
I'm laying out my first tube amp build since I was a teenager, as I now resume that lost hobby in retirement 50 years later!
I'm laying out my first tube amp build since I was a teenager, as I now resume that lost hobby in retirement 50 years later!
If you are looking 'top down' - do you mean 'vertical mount style' as shown in linked page?
https://dalmura.com.au/static/Page%2018%20from%20Hum%20article.pdf
Leakage flux egresses out the winding sides.
By ferrous, do you mean steel, rather than say aluminium bell-ends?
https://dalmura.com.au/static/Page%2018%20from%20Hum%20article.pdf
Leakage flux egresses out the winding sides.
By ferrous, do you mean steel, rather than say aluminium bell-ends?
Covers are there for safety and to pretty things up. Their influence on magnetic flux is minimal, if at all.
The most significant magnetic flux will be in the direction perpendicular to the direction of the windings on "classically" wound transformers. It is a very good idea to account for this in layout.
For toroid transformers, the most significant flux is in the direction perpendicular to the core opening. Woe is the builder who attempts to stack toroid transformers....
The most significant magnetic flux will be in the direction perpendicular to the direction of the windings on "classically" wound transformers. It is a very good idea to account for this in layout.
For toroid transformers, the most significant flux is in the direction perpendicular to the core opening. Woe is the builder who attempts to stack toroid transformers....
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I don't know for aluminium covers but it works for steel covers.
A simple test can be done, that's what I do when building a new amplifier..
1) connect the primary PT to the mains, nothing else.
2) connect a pair of headphones at secondary OPT, nothing else.
3) listen.. then move the PT/OPT.
A few millimeters can change A LOT the result (noise).
Now put a steel cover, lower noise. Insert a steel "sheet" or two (1mm) between covered PT and OPT and listen.
From my "experimentations", it is better to shield the PT than the OPT.
When using EI transformers, I turn them 90° in two axis.
In this diagram I'm thinking the typical horizontal wound transformer where the whole coil is above the chassis with no need to make a large rectangular hole in the chassis, that type. By ferrous I mean a transformer cover alloy containing iron. So looking top down it appears I can assume I have a longer arc of energy coming out of the tape covered coils than the iron laminate/bracket sides, logical. Because it's elliptical not a circle, aiming the flux is possible instead of sending it right through the first preamp tube. Since I'm using covers it may even be possible to mount the X former 45 degrees sending the flux harmlessly off the corner of the chassis, then cover it so it looks like a 90 degree mount.
Try it some day with a large piece of Perspex and some iron filings. Its a nice kid's physics experiment! I had fun doing it some years ago with my daughters.
Also, the covers are typically on the wrong end of the primary flux direction, aren't they? The primary flux on EI transformers typically flows out from the direction of the laminations. I will look for a picture and post it..
Ian
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I should append my answer, since Steel covers also help reduce transformer noise too. Steel is more rigid than aluminium and can definitely reduce transformer vibrations, especially for Power and chokes I suppose.
Yes, Steel can also shield a little bit, but its density is also not really enough for "real" shielding in my opinion. That is why I noted it has "minimal" effect in my post above. Also, if you want to use steel as a shield, I am pretty sure that the effects will diminish over time. Perhaps stainless steel would be a better choice. Or better yet, employing a better layout
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An EI transformer's flux looks much like that of a horseshoe magnet. This picture is very similar to what my daughters observed:
There is of course flux from the sides, but consider much of this is actually caught up in the thickness of the windings of your transformer. Yes, some spacing is wise here too. But consider that the the flux at the ends will be very significant, and there is no covers or extra space (the windings proper) there...
Magnetic flux is a property of any correct functioning transformer. Best is to work on a proper layout and avoid overlapping magnetic flux.
Ian
An externally hosted image should be here but it was not working when we last tested it.
There is of course flux from the sides, but consider much of this is actually caught up in the thickness of the windings of your transformer. Yes, some spacing is wise here too. But consider that the the flux at the ends will be very significant, and there is no covers or extra space (the windings proper) there...
Magnetic flux is a property of any correct functioning transformer. Best is to work on a proper layout and avoid overlapping magnetic flux.
Ian
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Also better than Steel alone... Mu-metal, a nickel–iron soft ferromagnetic alloy with very high permeability. It is most often used in shielding of microphone and phono step-up transformers for audio, but has many other applications.
I quote Wikipedia:
Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area.
Also: The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.
I quote Wikipedia:
Magnetic shielding made with high-permeability alloys like mu-metal works not by blocking magnetic fields but by providing a path for the magnetic field lines around the shielded area.
Also: The effectiveness of mu-metal shielding decreases with the alloy's permeability, which drops off at both low field strengths and, due to saturation, at high field strengths. Thus, mu-metal shields are often made of several enclosures one inside the other, each of which successively reduces the field inside it. Because mu-metal saturates at such low fields, sometimes the outer layer in such multilayer shields is made of ordinary steel. Its higher saturation value allows it to handle stronger magnetic fields, reducing them to a lower level that can be shielded effectively by the inner mu-metal layers.
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