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Old 19th September 2013, 10:06 PM   #1
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Default Rectifier and DC filtering relationship question

I tend to like low filtering for that saggier feel in guitar amps. I've been studying some tube sheets and finding various uF requirements on different rectifier tubes. If a rectifier tube requires a higher capacitance, does that mean that it's not reducing as much ripple as the rectifiers that require lower capacitance?


Or is it that the tubes rated for higher capacitance are rugged enough to handle the current demands that bigger filtering is capable of needing, and one could always use a lower rated filter than spec'd?
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Old 19th September 2013, 10:22 PM   #2
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Why don't you download PSUD2, and model tube power supplies. That way you can see first hand how different configurations reduce ripple etc.

PSUD2

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Old 19th September 2013, 10:24 PM   #3
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Quote:
Originally Posted by Sea Biscuit View Post
Or is it that the tubes rated for higher capacitance are rugged enough to handle the current demands that bigger filtering is capable of needing, and one could always use a lower rated filter than spec'd?
That is correct. The rectifier is fine if you use a lower value capacitor, but ripple increases.
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Old 19th September 2013, 10:25 PM   #4
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The first part is wrong. The second part is right. The filter caps act as a significant additional load on the rectifier and power tranny. I'd recommend rectifier and tranny current rating specs that are twice what you think the circuit alone will draw.

What I did in one of my smaller guitar amps (5 watt) was to filter the ripple out real well with large caps, and then do an R/C to design in the sag. I also rectified the 6.3VAC (or was it the 5 volt tap?) and ran at least the input tube filiment on well filtered DC for minimum hum (there isn't any). If you go the DC filiments route, my research convinced me that it's worth trying to get it to be exactly 6.3VDC, for max tube life.

By the way, rectifier tubes are obsolete. Solid state diodes are much more energy efficient (less heating of the power tranny), and just as good in any other way.

Last edited by Bob Richards; 19th September 2013 at 10:27 PM.
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Old 19th September 2013, 10:29 PM   #5
chrish is offline chrish  Australia
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You are thinking about it the wrong way. The uF stated is not a requirement as such, it is a limitation. A lower limit does not mean you need less uF for the same ripple, it is stating that the rectifier in question cannot handle the current require for increased capacitance.
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Old 19th September 2013, 10:33 PM   #6
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ok cool. got it. And I will check out PSUD2. It's already on my computer but I've never used it...
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Old 19th September 2013, 10:35 PM   #7
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No time like the present.

jeff
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Old 19th September 2013, 10:36 PM   #8
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Originally Posted by pmillett View Post
That is correct. The rectifier is fine if you use a lower value capacitor, but ripple increases.
Oh and btw, I figured out what was causing the ebay links to break. It's a setting in the USER CP of this site. Go to EDIT OPTIONS and change the MESSAGE EDITOR INTERFACE to STANDARD, and then when you post ebay links they will work.
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Old 19th September 2013, 11:23 PM   #9
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So in that program, does this mean that I would still have about .45v of A/C on the line?


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Old 19th September 2013, 11:55 PM   #10
jjman is offline jjman  United States
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I think of voltage ripple there, not current ripple. Choose the V on C1 button and re-simulate.
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