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Old 1st March 2005, 02:03 AM   #1
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Default Power Supply Question

I'm using a modified choke input power supply with a 5U4G rectifier followed by a 1uF capacitor feeding a 10H choke followed by another capacitor then another LC section. The supply runs at about 800VDC. What voltage rating should the 1uF capacitor have? PSUD simulations show high voltages appearing at the input of the first inductor, but I'm not sure how to interpret what's happening. TIA.

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Old 1st March 2005, 02:45 AM   #2
cominup is offline cominup  Viet Nam
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Dear serengetiplains,

In my opinion, usually, voltage of cap = 1.5 times max voltage. Then, after rectifier valve, caps can be appx. 50uF for safety of rectifier valve; but, someone used 100uF for more bass. He said that cuz of slowly to search the max of valve, so there would not any damage to rec. valve. In fact, there is really more bass.

I am using in // of one pollar cap and one oil non-pollar cap rite after rec. valve. It's good and get very slow tubey sound.

In case of 800V; and you could not find some cap at 1500V; you can // a bunch of cap; it's pretty cheaper and more dynamic sound.

Good luck and keep safety; 800V it's so high voltage.
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Old 1st March 2005, 06:28 AM   #3
garbage is offline garbage  Singapore
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my experience with psud2 is that it's a very accurate tool... provided that all values are keyed in correctly, and the correct current source put in to simulate the current drawn by the load.

when the above is done, just take the highest voltage (transient) seen by that cap plus a little headroom. this value should give a comfortable working voltage for the cap.

i did the above for my psu, and i never worry when switching them on.
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Old 1st March 2005, 01:28 PM   #4
Sherman is offline Sherman  United States
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Quote:
Originally posted by cominup
Dear serengetiplains,

.... Then, after rectifier valve, caps can be appx. 50uF for safety of rectifier valve; but, someone used 100uF for more bass. ...
Good luck and keep safety; 800V it's so high voltage.

The first cap after a 5U4-G can be 40uF MAX for capacitor input. Latter caps can be larger.

As for voltage of the caps- in my new monobloc I am using a 5U4-G followed by a 40uF and 8H choke and a 100uF for a B+ of 430VDC. Putting my meter on the B+ I see the voltage go from zero to about 520 very quickly and then settle back to 430 over the next 10 or 15 seconds.

Based on that and to provide a safety margin make the caps 1.5 times your B+. Higher won't hurt.
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Old 1st March 2005, 02:34 PM   #5
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Put two 370VAC motor runs in series with balancing resistors across them. This will give you 1200VDC at 1uF. 440vac motor runs would bring you up to ~1600VDC. Cheap and good from ebay.
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Old 1st March 2005, 03:55 PM   #6
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Thanks for the advice, guys. Have a great day.
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Old 1st March 2005, 11:42 PM   #7
garbage is offline garbage  Singapore
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Quote:
Originally posted by pedroskova
440vac motor runs would bring you up to ~1600VDC. Cheap and good from ebay.
regarding motor run caps, there were extensive discussions on AA that GE dielektrol caps are the best to go.

i got mine from ebay as well. but shipping to my location killed me.
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Old 2nd March 2005, 05:23 AM   #8
cominup is offline cominup  Viet Nam
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Dear all,

one more things, when I built tube amp, I was using so much old parts to save money and turn back time also. On caps' label, we can see 400V; 400VDC; 400WV. Is there any different rite here??? May be WV means WORKING VOLTAGE? so, what is max voltage?

...
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