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Old 30th May 2006, 03:39 PM   #1
sbelyo is offline sbelyo  United States
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Default PSU question? Going tube rectified

I'm building this amp
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The artice says the max output current is 20 ma

Here's the psu
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I'd like to use a 5U4GB retifier because I have a bunch laying around and a 235-0-235 @270ma transformer. I put some values into PSU designer but I'm not shure about the rectifiers limits? How should I change the capacitors values so that it's within the rectifiers range?
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Old 30th May 2006, 04:09 PM   #2
poobah is offline poobah  United States
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Why do you consider it out of range at the moment?

I don't believe PSU II takes tube warm up into consideration when it sims. So you could ignore excess current messages during the first few seconds anyway.

BTW, 100 uF, seems off the charts for a headphone amp.

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Old 30th May 2006, 05:29 PM   #3
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I may be wrong but i think 47uF is max for C1. C2/3 are fine.
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Old 30th May 2006, 05:37 PM   #4
SY is offline SY  United States
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You are not wrong- the 100uF cap will kill that rectifier dead. 40uF is much more reasonable.
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Old 30th May 2006, 05:41 PM   #5
poobah is offline poobah  United States
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SY,

The Cath. Fol. output has good PSRR anyway doesn't it?
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Old 30th May 2006, 06:08 PM   #6
rdf is offline rdf  Canada
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R1 and R2 are only 220 ohm. The parallel combination with the trailing 100 uF caps might make even 40uF for C1 a stretch. If you have the parts you might want to consider replacing R1 and R2 with chokes or going smaller for C1.
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Old 30th May 2006, 06:10 PM   #7
SY is offline SY  United States
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I haven't tested mu followers, but presumably...

With proper grounding and reasonable filtering, getting the supply noise down should be no trouble anyway. The nice thing about the input cap limitation is that the ripple currents will be low.
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Old 30th May 2006, 06:14 PM   #8
Merlinb is offline Merlinb  United Kingdom
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Is it the in-rush current that limits the size of a capacitor after a valve rectifier? Is there a way to calculate the in-rush current- is it related to the time constant somehow?
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Old 30th May 2006, 06:40 PM   #9
SY is offline SY  United States
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No, it's the peak ripple current that's the bad actor here.
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Old 30th May 2006, 06:47 PM   #10
sbelyo is offline sbelyo  United States
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I read on the 5U4GB data sheet that max input cap is 40uf so I'll change C1 to 40uf

Now C2, and C3 Is it okay to use say 150uf? And if I increase the value of the resistor, do I have to increase the wattage?
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