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Old 2nd April 2011, 12:03 AM   #21
dobias is offline dobias  United States
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Gentlemen,
My transformer has a 436-0-436vac output.
Using a CL filter the rectified output would be 1.4 x 436 = 610vdc.
Using an LC or LCLC filter the rectified output would be 0.9 x 436 = 392vdc.
The 2A3 output tubes are rated at 350vdc.
Please keep the discussion on LC filters.
Frank
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Old 2nd April 2011, 05:11 AM   #22
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PSUD is a lovely power supply simulator. That's all it does, and it does the job brilliantly, with traces for looking at voltage or current through any element of the supply. The parts list even contains the exact rectifier you want.

PSUD2

Geek-Bob says two solder-burned thumbs way up!

Last edited by DSP_Geek; 2nd April 2011 at 05:13 AM.
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Old 2nd April 2011, 03:31 PM   #23
dobias is offline dobias  United States
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Geek-Bob,
Thanks to your suggestion, I tried it one more time & this time I managed to make it work!
The trouble I have now, as a newby, is information overload with that program.
Frank
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Old 2nd April 2011, 05:54 PM   #24
jdg123 is offline jdg123  United States
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I have been watching with keen interest a few people debate cap size in power supplies. One fair observance is that large caps when depleted call for gobs of current to replenish. If you have accommodated that lust for current with sufficient L so that that L can supply the demand for current through its collapsing field, then large C is good. Further, diode isolation of large C can assist in gaining from large C's low resistance and grand ability to filter ripple without discharging them so their hunger for current comes into play.

Lundahl is trying to sell you transformers but that's OK. They have been poo pooed for being expensive and heavy but dang, they do good things when properly applied. I'd follow their (Lundahl's) advice and stay away from very large caps with the above/given caveats.
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Old 3rd April 2011, 02:22 PM   #25
dobias is offline dobias  United States
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jdg123,
Unfortuneately, I can't afford Lundahl. I'm just trying to pick their brains. The "mystery" power supply I picked up for a song had a Merit 436-0-436 vac PT, a large Thordarson swinging choke 5-20H 300mA, & two smaller Stancor 4.5H 200mA chokes.

I'm very interested in more explanation of applying "diode isolation". Can you point me in the right direction ? Is this similar to having a tuned resonance choke with a small bypass cap?
Frank
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Old 3rd April 2011, 09:53 PM   #26
jdg123 is offline jdg123  United States
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I am told it was covered in the radiotron handbook in '64 but I only had a few weeks with one I got from the library and never did find the section (It was sort of like the fog that descends at a video store-forgot about any subject of interest as it was soon displaced by another!)

My experience with diode isolation is through a fellow SET12 on the audiokarma site. I have heard his rig using 811-10 triodes and diode isolation with very low DCR. It rocks! Superbdynamics!

Basically after each C in a CLCLC C power supply the last C something around (40uF) can only be recharged by current passing through the chokes and not by the large caps that are doing the filtering because after each C (save the last) there is a diode preventing the discharge from going "forward" to the next cap. The first cap is chosen by rectifier choice, the next two are very large, 1000uF and then the last "reserve" resistor about 40uF.

The tuned resonance, if I catch your meaning, is about the nature of power supplies that begin with a choke. Read some good stuff on that today under a google search of SEAmplifiertheory and Resonant-choke Power Supply. For cap size choice, in the end, you are going to have to feed the cap that feeds the plate. Caps eat current, not milliamps but Amps! Managing that cycle of discharge and charge is a trick. I'd love to see it broken down by the nanosecond but I've not met the man or the program that explains it so.

I invite you to explore SET12 threads on power supply as well as the ones mentioned above. Don't worry about finding THE answer. I've been convinced that low DCR and diode isolation is a great combination for a SET. I decided by listening and logic. Good luck!
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Old 4th April 2011, 09:43 AM   #27
DF96 is offline DF96  England
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If I understand correctly you are saying that diodes are inserted in series with each smoothing choke. Why? It is hard to think of a scenario in which these diodes will do anything other than forward conduction under 'normal' conditions. Are they intended to suppress subsonic ringing caused by using caps which are far too big?

Quote:
Caps eat current, not milliamps but Amps! Managing that cycle of discharge and charge is a trick. I'd love to see it broken down by the nanosecond but I've not met the man or the program that explains it so.
I'm not sure I know what this means. Maybe that is why nobody has explained it?
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Old 4th April 2011, 12:57 PM   #28
jdg123 is offline jdg123  United States
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If the caps you use are all linked, like soldiers, when one, say the last in the series just before the plate of the output tube, discharges even a little bit, the others will lend current. Mind you I am not an EE. I am relaying to you what has been told to me...These others, the big ones, will then, due to their very low resistance call for all the current there is in your power supply until they are fully charged. It would be better to only have that last cap to charge rather than have the big ones lend it current but you need the big ones for their filtering duties. The solution is to keep them from lending their voltage by isolating them from the ones forward through diodes.

As far as looking at the rush of electrons in terms of nanoseconds it makes sense to me! They travel (even having to accelerate across free space of the vacuum tube) at 200 million miles an hour, they get around. If you want to look at the cycling of those caps you are wondering about then you'd need to know how much charge is moving and how fast (it accumulates), the when and where of the needs of each device, through the whole amplifier! Everything is linked, not at the speed of thinking or even the human heart but at the speed of (nearly) light (and of course at one end it all changes direction at approximately every 60th of a second,) everything effects everything else. Hopefully, every part is needed.

Truly, there has been little spoken about the amplifier as a complete unit save some sonic reviews... All of us on this site and others seem to be slightly confused about some little aspect of how the thing works, we follow those before us and make a few stabs and changing values or arrangements based on again, those who came before us...much, much before us.

Don't get me wrong, I am impressed how much the good men and women of science and industry have learned to manipulate electrons and chemistry but I don't think we have it all down. If we did there would have been established by now the "right" way to build...well, anything! I'd just love to see one devoted scientist develop a comprehensive series of events for a simple system like an SET as has been done for the human genome project. It may not be that complex or important but I can't help but want what I want :-)

Cheers!
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Old 4th April 2011, 01:22 PM   #29
DF96 is offline DF96  England
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If the diodes are in series with the chokes then they won't do what you seem to be describing. If they are in series with the caps then they might do what you are describing but this seems to me to be a bad idea. Why include big fat smoothing caps, then stop them from doing their job by isolating them with diodes? The caps would simply charge up to the highest voltage ever applied, then the diodes switch off and you might as well remove the caps altogether as they no longer do anything. I hesitate to dismiss an idea without investigating it, but it sounds completely daft to me. Maybe I have misunderstood your description, or maybe you have been sold snake oil. Perhaps you could post a diagram or a link to where this idea is discussed?

Talk of nanoseconds is merely adding confusion. Components isolated behind diodes clearly are not needed. Plenty of science has been applied to audio, but some people either don't understand it or don't believe it. More science would help, but mostly would still be misunderstood or ignored.
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Old 4th April 2011, 02:26 PM   #30
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I'm not an expert on this subject, but I would say that there are three key concerns to sizing an LC, CLC, etc. power supply filter.

1. Desired input ripple (120Hz or 100Hz for a full-wave rectified supply) attenuation level. The inductor(s) and the capacitor(s) of the main supply filtering form an A.C. voltage-divider network. Having both Ls and Cs makes a resonant multi-pole filter. Multi-pole filters are more effective, but the resonant nature of a LC type filter needs to be accounted for as mentioned in the next concern.

2. The characteristic impedance of a resonant LC type filter should be determined, as you will need to ensure that there is enough series resistance within the filter so that the capacitors and inductors don't have undamped ringing at their resonant frequency, and potential low impedance loading of the power transformer. Or, ensure that their resonant frequency is below any which the filter might be presented with. Usually, but not always, the series inductor has enough winding resistance to satisfy this concern.

3. Desired maximum A.C. output impedance of the supply at the lowest frequency which the load might demand current, usually taken to be 20Hz for audio applications. Remember, the D.C. output impedance of the supply will include the series inductor's winding resistance, while the shunt capacitor will present an infinite impedance. As the frequency of the load's current demand rises the inductor presents an increasing output impedance while the shunt capacitor presents a decreasing one. In effect, the audio band output impedance is the parallel combination of those two impedances at a given frequency.

Said another way, the A.C. output impedance at a given frequency, along with the current demanded by the load at that frequency, will determine the ripple voltage on the D.C. supply rail. So, you would want to set a maximum D.C. supply rail ripple voltage depending on the power-supply rejection ratio of of any following regulator and of the amplification circuit itself.

There are any number of resources for the relevant formulas which to calculate such values . Here's one that google found right off.

Elliott Sound Products - Linear Power Supply Design
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Last edited by Ken Newton; 4th April 2011 at 02:49 PM.
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