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DCR requirments for Chokes
DCR requirments for Chokes
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Old 15th August 2019, 04:02 PM   #11
sumotan is offline sumotan  Indonesia
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Thanks for the tutorial Keit. Learn something new everyday. At my end it's 100hz,
how do you arrive at the value of the cap to use ? Curious to try out some time.

Thank you again
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Old 15th August 2019, 04:50 PM   #12
Keit is offline Keit  Australia
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Sumotan: To calculate it is somewhat involved and depends on some uncertainties, particularly for low values of the first filter cap.

The best approach is C = 1 / (4 L pi-squared f-squared)
where C is the shunt capacitor in farads, L is the choke rated inductance in henries, f is the ripple frequency in Hz, pi is 3.14... .
Try that value as a starting point, and then go down in 5% increments until you spot the optimum ripple reduction.

Note that the cap may operate under some stress if the initial ripple is quite high in a high power amplifier. This is about spending money on a capacitor to save money in the choke. It's not particularly recommended. Just another option. These days, if you have got a bit too much ripple, just put in a bigger second electrolytic. There's no limit other than your wallet. (Don't increase the size of the first electrolytic beyond the rectifier tube ratings - all tube rectifiers have a maximum allowed first filter capacitance. If this capacitance is exceeded, they can arc over internally, with dramatic results.) When tubes were king, you couldn't get electrolytics in decent sizes.
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Old 15th August 2019, 05:40 PM   #13
sumotan is offline sumotan  Indonesia
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Thank you again Keit for the advice.

Cheers.
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Old 15th August 2019, 05:40 PM   #14
cerrem is offline cerrem  United States
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To answer your question, The DC resistance is basically a loss.... You try to keep it minimized else the inductor would be HUGE to accommodate to large of a wire gauge... The DC resistance and Inductive reactance are added vectorially ..... The DC resistance in some cases decrease the Q of the LC resonant tank circuit.... ie it can help "dampen" the resonant frequency peak in circuits that could otherwise ring, which can be a good thing, due to the fast change in phase angle..
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Old 15th August 2019, 05:51 PM   #15
sumotan is offline sumotan  Indonesia
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Thank you kindly Cerrem. The reason that I put forth this question was while surfing I came across an article saying LC inductors should have dcr of no more then 200 ohm while CLC can be higher. I've never come across such recommendations when I was reading up of tube articles, hence.
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Old 15th August 2019, 09:37 PM   #16
claudiomas is offline claudiomas  France
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in practice for LC filter swinging choke higher DCR means higher noise so the best compromise is a low DCR especially for high voltages while in CLC smoothing choke the noise is minimal so DCR can be high if you want so I agree with the article
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Old 16th August 2019, 07:12 AM   #17
6A3sUMMER is offline 6A3sUMMER  United States
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For a true choke input filter, you need to meet the rule for critical inductance:
Critical Inductance = 350/(current in mA)

A choke input filter for an amplifier that needs 80mA DC will need an inductor of:
350/80mA = 4.375 Henry. Use a 5 Henry inductor.

A choke input filter gives DC volts that is 0.9 x rms Volts. A full wave 400-0-400 VAC primary is rectified by low voltage drop Schottky diodes. The DC voltage out is 400 x 0.9 = 360VDC. As stated earlier, you need a choke that is rated for choke input service application. Otherwise, stick to capacitor input supplies.

Last edited by 6A3sUMMER; 16th August 2019 at 07:15 AM.
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Old 16th August 2019, 07:51 AM   #18
claudiomas is offline claudiomas  France
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the question was about DCR between swinging and smooting choke DCR and 6A3summer you do not consider coil res DCR and for HV valve psu consider 10H racomanded value in real world swinging choke DCR should be as low its possible for low noise and better regulation i think Schottky diodes rectifiers etc good only for heather and smps
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Last edited by claudiomas; 16th August 2019 at 07:54 AM.
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Old 16th August 2019, 09:46 AM   #19
6A3sUMMER is offline 6A3sUMMER  United States
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claudiomas,

I mentioned some facts, in case the original poster might be interested in using a choke input power supply.

As was already said, low DCR is important. I was not going to repeat what had already been said.

Failure to follow the critical inductance rule is allowed. But if you do, the power supply is not a true 'choke input' power supply. It will not output 0.9 x the rms volts, but will in fact be more toward a cap input filter supply (outputs up to 1.414 x rms volts). If you observe Both critical inductance, And low DCR, you will get good power supply regulation versus load current.

There are HV Schottky diodes (or even if there are not any), then . . . Whatever reasonable solid state HV diodes you use, they have lower impedance and voltage drops than tube rectifiers that are commonly used in the same circuits. As such, the solid state diodes also give better voltage regulation versus current when the filter is a true choke input.
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Old 16th August 2019, 01:37 PM   #20
claudiomas is offline claudiomas  France
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thanks 6A3summer for the point valves in psu are most protecting the DUT or OPT or amplifier wathsoever also sometime look great if any problem the valve will not over destroy and short anything, with diodes if any moskito fly in the wrong way the diode go short and your opt tamura tango etc bye bye many time i get amplifier on the repair bench with power transformer and one OPT dead @ the same time killeds by one small cheap diode, so if somebody really want use diode rectification way not insert one valve just to protect and give the other tubes the time to be ready to draw current before HT come on

cheers
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