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DCR requirments for Chokes
DCR requirments for Chokes
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Old 24th August 2019, 02:01 AM   #71
jhstewart9 is offline jhstewart9  Canada
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Smile Another Resonant Filter

Long before I got myself a copy of Beitmans schematics of 1930s radios I'd tried a couple of resonant PS filter systems. It was simply a matter of connecting caps in parallel with the choke & watching the scope. This is one of those.

I'd also tried using a heater transformer secondary as a choke for a low voltage, higher current supply, the primary resonated with a cap. The cct is here somewhere, I'll try simulating that later.

There are several examples of both in Beitmans 1930s receiver ccts.

The amp I pulled off the shelf is a lot heavier than I recall, must be caused by age, mine! This amp has not been run in at least 40yrs. The caps are most likely shot.

50W Amp Pre1960 with Resonant Choke Filter PP 6550s or KT88s, Pentode Connected, 50W+
Hammond 1700 Series OPT 5K P-P
Separate Hammond Transformers for Plate & Heater Supplies
Surplus No Name Choke Regulated Screen Supply,
7AU7 both sections paralleled_6AU6 error amp_991/NE16 ref 6AU6, then 6SN7 Both Sections
Paralleled Phase Splitter AC & DC Balance Controls & Fixed Bias Adjust

The HV PT & Choke Resistance measured today. HV PT Primary R is an estimate. The actual measured HV at the first cap was 520V at the time of build. Needs some numbers for the filter cap ESRs for the simulation to have better accuracy. Estimate for the 5AR4 rp are from RDH4 p1171
Attached Images
File Type: jpg 50W Amp Using Resonant PS Filter A.jpg (97.3 KB, 73 views)
File Type: jpg 50W Amp Using Resonant PS Filter B.jpg (152.3 KB, 75 views)
File Type: jpg 50W Amp Using Resonant PS Filter C.jpg (98.2 KB, 73 views)
File Type: jpg 50W Amp Using Resonant PS Filter D.jpg (145.5 KB, 74 views)
File Type: jpg IMG_4353 50W Amp LHS E.jpg (312.4 KB, 70 views)
File Type: jpg IMG_4354 50W Amp Underside E.jpg (644.3 KB, 30 views)

Last edited by jhstewart9; 24th August 2019 at 02:04 AM. Reason: error
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Old 24th August 2019, 02:34 AM   #72
Keit is offline Keit  Australia
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Quote:
Originally Posted by jhstewart9 View Post
I'd also tried using a heater transformer secondary as a choke for a low voltage, higher current supply, the primary resonated with a cap.
That would not be efficient use of components as a heater transformer would have no air gap and so the core would saturate at quite low current. And of course the DCR is twice what it needs to be for the window size, as there are two equal volume windings instead of only one.

You may get nearly the same ripple suppression for a given degree of regulation with a resistor instead of the transformer.
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Old 24th August 2019, 11:41 PM   #73
jhstewart9 is offline jhstewart9  Canada
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Default Yet Another Resonant Power Supply Filter

This one from a 1930s Brandes Radio. With very little in electrolytics manages a very respectable reduction in PS ripple.
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Old 25th August 2019, 12:01 AM   #74
jhstewart9 is offline jhstewart9  Canada
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Quote:
Originally Posted by Keit View Post
That would not be efficient use of components as a heater transformer would have no air gap and so the core would saturate at quite low current. And of course the DCR is twice what it needs to be for the window size, as there are two equal volume windings instead of only one.

You may get nearly the same ripple suppression for a given degree of regulation with a resistor instead of the transformer.
All too true. But I guess the core saturation was not near total, still got a cap to resonate the cct. I've used many Hammond 125 PP Series over 60 years in SE ccts with no problems. The LF performance is not great but for ordinary use it is OK. There were gapped SE OPT in the Hammond line back in those daze, don't recall ever buying one.

I'm not a critical listener, I don't try to analyze whether the Flugel Horn in the Orchestra is off key. For me the challenge is in the cct design. Beyond that there are many more important things to accomplish with my time. At present that would be using a chain saw & wood splitter to demolish the dead Ash trees here on this place. 4.4 Acres takes a lot of work. Been here 50 yrs.

The image is 3W & Baxandall Tone Contriols. There is a magnetic phono preamp or mike input. The OPT is a Jensen 2430 equivalent to the H125D. Probably made for them by Hammond. Built more than 50 yrs ago, in everyday use, including today. Still sounds OK.
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File Type: jpg 3 WATT AMP RHS 9W 20C.jpg (102.0 KB, 25 views)
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