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Electrostatic screen in OPT. Is there any benefit?

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#22
JonSnell Electronic said:
The patent speaks of a novel negative feedback system, which is common knowledge but the use of the screen, acts as a shorted turn, reducing the need for an air gap to allow the field to collapse easier than if there was no air gap.
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trobbins said:
Is this a comment on Bereskin's US2924780 ? I don't see any comment about applying the inter-winding screen to act as a shorted turn?
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I don't see any benefit from a short turn in any transformer, it even seems to be disadvantageous instead, preventing power from being transformed from the primary to the secondary and converting it into heat. Perhaps there's been a mix up with a belly copper foil?

Later this day I hope to find an advice for a PP output transformer, designed and published by TELEFUNKEN in the 1950ies, which features electrostatic shield windings beneath and in top of the galvanically isolated NFB winding.

Best regards!
 
#23
There are drawings in Bereskin patent. https://www.google.com/patents/US2924780
One of the shows a diagram with tubes in another drawing of the transformer. The diagram with tubes shows in general form that the feedback winding is surrounded on all sides by a screen. In the transformer drawing, it is clear that there are no short circuits in this circuit, because otherwise the transformer would be disturbed due to a short circuit. In general, I still expect from English speakers the most accurate translation of the explanatory part of his patent.
Thankee!
 
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#25
Dr. Bereskin provided me with some materials not long before he died, that I have posted on my books web site (near the bottom of the page) here:

Vintage data

One of the papers gives detailed construction notes about this OPT and the amplifier it is used in, but I didn't see a concise description of why the ES shield is in there. But I didn't read it all carefully.

Pete
 
#28
pmillett said:
In one of the other papers, it's clear that the purpose of the ES shield is to reduce capacitance from primary to the dedicated feedback winding. He said that this allowed much more NFB to be used.

Intuitively it sort of makes sense...

Pete
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I don't see that pri-sec parasitic C has to degrade phase margin - seems like you could make add phase lead

a shield typically has as much or more parasitic C to each winding

with a grounded shield then you definitely getting a roll off on both windings
 
#29
pmillett said:
Dr. Bereskin provided me with some materials not long before he died, that I have posted on my books web site (near the bottom of the page) here:
Vintage data
One of the papers gives detailed construction notes about this OPT and the amplifier it is used in, but I didn't see a concise description of why the ES shield is in there. But I didn't read it all carefully.
Pete
Click to expand...
Thank you so much! I was just looking for a biography of Bereskin. You are very fortunate that you knew him, and touched the engineers of the old school. It is very interesting that he was born in the US in 1912, most likely his parents brought him to Vladivostok five-year-old child. Yes, then this city was Russian but not Soviet and not Siberian as it is written there. This region is called the Far East. This is not Siberia. I've been there many times, about him they say it's Russian San Francisco. It became Soviet only in 1922.
Here on the forum wrote that he worked for Phillips, and there he studied litz. But the biography of this is not an exact mention, although it is indirectly seen that he engaged in similar studies all his life.
I noticed that in the secondary winding of his output transformer there is a thick wire. Apparently, he ignored the possible skin effect in this winding.
 
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#31
In the next branch we discussed the application of Litz and the skin effect. You quite rightly wrote that the sound frequency range is not very wide, but this frequency range in the output transformer is the same for both the primary and secondary windings. However, the diameters of the wires in the primary and secondary windings are different, hence the skin effect can be manifested more strongly in the thick wire of the secondary winding. Nevertheless, Bereskin ignored this effect even in the thickest wire. However, it should be noted that the insulation of the enameled wires in its primary winding is reinforced with cotton to reduce the capacitance between the wires in its bifilar winding and to increase the electrical strength. Information about this combined isolation with cotton in the secondary winding, I did not see.
 
#33
This is achieved by minimizing both winding capacitances and stray inductance. If you observe a higher resonance frequency on a tranny that features litz wire, I suspect this results from just smaller winding capacitance, due to more isolating material (enamel plus cotton) in comparison with solid magnet wire.

Best regards!
 
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