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In Reply to: RE: Correction posted by deafbykhorns on August 18, 2015 at 19:51:02
I recommend to use chokes in the "ground" line (C3-L4-C5, and C5-L5-C6).
Commercial chokes don't like kV voltage between coil and bondage, even the choke's bondage isolated from mounting plate.
Up to 1kV I use Tungsram PV200/1000 (200mA) dual rectifiers.
Follow Ups:
In this post from nearly ten years ago, the ARRL Handbook is quoted. Note the specific statement that chokes in the ground line are avoided in radio receivers and audio amplifiers due to excess hum.
If you click on RayP's post (to which Jimmy's is a reply) you will find a more extensive discussion. Especially note Ed Sawyer's post, where he found 1000mV hum with this topology, which was reduced to 2mV when the choke was moved back to the high-voltage side.
The ARRL often get things wrong. I'd like to see an analysis of the current path and quantities involved, not just a statement in text.
"With this connection [choke in negative side], the capacitance of the transformer secondary appears in parallel with the filter chokes tending to bypass the chokes."
How much transformer capacitance (XC) are we talking about? Is it really significant at 120Hz in terms of the output impedance of the transformer winding? I'm highly skeptical of the claim here that Ed's result (1 V ripple VS 2 mV) was due to this effect.
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Buy Chinese. Bury freedom.
To do a useful analysis, you must first determine the power transformer's winding design. When I tried to explore that last night, I came up with a very complicated circuit!
In the first analysis, the capacitance between a winding and an adjacent core (which is chassis/safety grounded) will be several hundred picofarads - not a big deal at 120Hz, but enough to pass tons of diode switching noise and other HF junk. It greatly exceeds the self-capacitance of the filter choke winding.
More realistically, consider a primary winding adjacent to the core, followed by a HV winding with the center tap in its middle. Further assume the power line neutral is adjacent to the core. Then there is a capacitance from neutral to chassis ground (the core) in parallel with the house wiring which grounds the neutral line at the power entry box. Between the hot side and neutral of the primary there is a voltage source of 120v. From the hot side to the secondary is another capacitance, followed by anther voltage source of the HV half winding, to the center tap. All of this is in parallel with the filter chokes. Lots of opportunity to induce noise bypassing the choke impedance.
At that point, realizing it was both complex and dependent on the design of the specific power transformer, I went to bed. :^)
HF noise is a different problem. I was responding to the claim regarding increased ripple ("excess hum") from this topology. I don't see any reason why that would happen, and I don't think anyone should assume it's a factual statement just because it was published by the ARRL. :)
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Buy Chinese. Bury freedom.
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Like this 850V PSU.
Output voltage significantly depends on the secondary DCR (at given output current).
Some transformer manufacturer datasheet contains output voltage at nominated current, so unloaded voltage is different, even much greater. If power transformer secondary coil is made my thicker wire (lower DCR), the voltage drop (between unloaded and loaded conditions) is smaller. This transformers are better.
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