Hi guys!
In the 1950s and 1960s, an electrostatic copper foil shield between the transformer sections was widely used in output transformers. Now do not apply. And the geometry of sectioning has not changed much. I propose to discuss, is there benefit from this screen in the output transformers?
In the 1950s and 1960s, an electrostatic copper foil shield between the transformer sections was widely used in output transformers. Now do not apply. And the geometry of sectioning has not changed much. I propose to discuss, is there benefit from this screen in the output transformers?
It is unusual to use a screen unless in a mains transformer and the sole benefit of an electrostatic screen, in a mains transformer, is obvious.
Yes. This article is from the journal for 1958. It has an amplifier on 807 tubes. The author is an old Jew from Odessa, a very authoritative author. A bit later, I am modifying the US patent from 1954 where also electrostatic screens are used in the output transformer. And the author is an American of Russian origin.
Unfortunately they both wrote and did not specify why the electrostatic screens in the output transformer, only mentioned that they are.
pa_g807
Audio amplifier system
US 2924780 A
Priority Date
Jun 30, 1954
The inventors of the invention
Bereskin Alexander B
The original patent owner
Baldwin Piano Co
https://www.google.com/patents/US2924780
Not sure this implies "widely used" as your original post suggests. Might there be a few out there? Sure.
Nevertheless, they used to be used and probably not from the whims or whims of the authors. In both these old transformers there are electrostatic screens, without mentioning the destination, as if this goes without saying. The power transformer also has a screen. I doubt to filter this interference from the network out again.
Although I read the patent carefully, maybe I missed something, in the description of the details, because I'm not a native speaker of English.
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Some years ago i disassembled an old Siemens OPT used in a 100 watt power amp with 4 EL34 , and there was inside at least 10 electrostatic copper foil between all the sections of this OPT connected to ground.
You can find and show here the circuit of this amplifier in order to better understand its features and why they used these electrostatic screen in OPT?
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. Plus adding to the insulation to avoid flash over, very rare on output transformers.
As, and judging by the dates from 1927, there has been ample time to develop this, if it was indeed, successful.
I would say that it was not as good as described, much like the majority of patents, as if it were, it would be widely used and is not.
As, and judging by the dates from 1927, there has been ample time to develop this, if it was indeed, successful.
I would say that it was not as good as described, much like the majority of patents, as if it were, it would be widely used and is not.
So far, I can see for sure that all these schemes unite, the presence of deep feedback and tetrodes or pentodes, that is, also of shielded tubes in the output stage. Perhaps this is due to the stability of the amplifiers in the presence of deep feedback and screening of the signal in the transformer passing through parasitic capacitances, which are difficult to control but which can cause instability and generation.
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We should not discuss irrelevant topics here.
Faraday shields may be useful in audio transformers because they disrupt capacitive coupling between windings. All high end interstage transformers that I had a chance to use had Faraday shields.
Capacitive coupling in an output transformer may be quite significant at high frequencies. I once measured it by applying input signal between one primary lead and transformer body. At 10 Khz, about 60% of normal secondary output was obtained. Capacitive coupling increases as interleaving increases. So, those state-of-the art transformers with 10 interleaves are one sure way to maximize capacitive coupling.
Capacitive coupling in transformers is bad because transformer's intrinsic capacitance is of poor quality. In addition, capacitive coupling disrupts transformer's symmetry at high frequencies.
Faraday shields may be useful in audio transformers because they disrupt capacitive coupling between windings. All high end interstage transformers that I had a chance to use had Faraday shields.
Capacitive coupling in an output transformer may be quite significant at high frequencies. I once measured it by applying input signal between one primary lead and transformer body. At 10 Khz, about 60% of normal secondary output was obtained. Capacitive coupling increases as interleaving increases. So, those state-of-the art transformers with 10 interleaves are one sure way to maximize capacitive coupling.
Capacitive coupling in transformers is bad because transformer's intrinsic capacitance is of poor quality. In addition, capacitive coupling disrupts transformer's symmetry at high frequencies.
About high end interstage transformers using shields: it depends if it is useful or not.
For example a 1:1 interstage transformer can perfectly do without a shield: here we want to maximize capacitive coupling by very close primary to secondary coupling, or even bifilar winding. A shield would not work good as we don't want to disrupt the capacitive coupling.
Interstage transformers with other winding ratios "might" benefit from shielding, but it depends on winding technique if it does or not; there is no golden rule.
About output transformers: for frequencies above some 5 kHz the transfer is capacitive. You can check this by measuring an output transformer with and without core (easily to do with c-cores). The influence of the core at high frequencies is approaching zero: you would measure the same HF bandwidth of the transformer with and without core. At lower frequencies the transfer is inductive; you need the core.
It depends on the properties of the core where and how the transfer switches from inductive to capacitive. For "good"capacitive HF transfer the winding technique is important (sectionizing; interleaving).
OT posts deleted. Please read the rules.
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?
At high frequencies, power transfer does not occur through the capacitance. Even if there is no core or it even air power transmission occurs through mutual induction of turns located very close due to partitioning or bifilar winding as in Berezkin. That part of the signal that goes through the capacitance in the bifilar winding becomes in-phase with the main current but still does not participate in the power transfer, since such a small capacitor will not be able to transmit any significant power to the load at 20kHz. But it is already possible to cause problems in the case of incorrect sectioning or non-bifilar winding, since signals from transmission by a parasitic capacitor and mutual inductance can become antiphase.
CORRECT!
In attach the figure already sent in another thread where is show the characteristic of the primary of two trafo when the load is not connected.
After the resonace the andament is capacitive but it doesn't means that the L disappaer!!!!!
Then there is a picture from Radiotron with a scheme of the equivalent trafo at high frequency; I hope this is clear for everyone
Walter
In attach the figure already sent in another thread where is show the characteristic of the primary of two trafo when the load is not connected.
After the resonace the andament is capacitive but it doesn't means that the L disappaer!!!!!
Then there is a picture from Radiotron with a scheme of the equivalent trafo at high frequency; I hope this is clear for everyone
Walter
Attachments
Walter, in your picture, it's clear that Litz has a thicker outer insulation!
It seems that with Litz-Q, on the contrary, it is even smaller and no more, as expected earlier.
And the second picture shows that at high frequencies the replacement circuit is much more accurate than that of MENNO VAN DER VEEN. http://www.next-tube.com/articles/Veen/VeenEN.pdf http://www.diyaudio.com/forums/tubes-valves/309086-amorphous-not-traffo-discussions.html
It seems that with Litz-Q, on the contrary, it is even smaller and no more, as expected earlier.
And the second picture shows that at high frequencies the replacement circuit is much more accurate than that of MENNO VAN DER VEEN. http://www.next-tube.com/articles/Veen/VeenEN.pdf http://www.diyaudio.com/forums/tubes-valves/309086-amorphous-not-traffo-discussions.html
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