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Old 27th May 2006, 06:56 PM   #1
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Default Volts AC rating in power supply caps

How many volts AC rating in the caps are sufficient for a power supply caps?
Iím building my first amp, Gordon Rankinís Bugle. www.wavelengthaudio.com/bugle.pdf

The Bugle schematic says PS caps: 2 * 100 uF, on a 330 VDC B+ line.
To convert to VAC, is it: 330 DC * square root of 2 = 467 AC??

And are there other factors apart from the formula, to adjust the needed VAC up or down?

Reason for asking:
While the formula yields 467, Iím wondering if I can use oil run caps rated 370 VAC, in lieu of the Rankin specced, but now n.a. Elna Cerafine caps, or better electolytics (Panasonic TSHA rated 450 VAC).

Thanks
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Old 27th May 2006, 07:38 PM   #2
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You got it backwards. The peak voltage of a sine wave = VRMS X 2^1/2. Divide 330 VDC by 2^1/2. Motor run caps. rated for 240 VAC or higher will do nicely.

In the 'lytic dept., use polarized Black Gates in place of the no longer available Cerafines.
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Old 27th May 2006, 08:17 PM   #3
knubie is offline knubie  Norway
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Yeah, all is well as far as most capacitors are concerned but exceptions exists, motor runs, for example ASC motor run caps are 440AC but 800 DC, almost twice the DC rating......
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Old 28th May 2006, 01:45 AM   #4
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(I had it the wrong way around, ok) but motor runs are an exception, mmm . .

Any views on polarized Black Gates v ASC motor run v better Panasonic (TSHA)?

Thanks
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Old 28th May 2006, 01:48 AM   #5
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Quote:
Originally posted by rick57
(I had it the wrong way around, ok) but motor runs are an exception, mmm . .
No, they follow the same rule.
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Old 28th May 2006, 01:53 AM   #6
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I've read two others at AA Tube-DIY say similar to knubie . .?

Hereís one:
http://www.audioasylum.com/forums/tu...es/100947.html

Maybe the different construction ďallows themĒ to have different electrical characteristics?
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Old 28th May 2006, 01:59 AM   #7
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Quote:
Originally posted by rick57
I've read two others at AA Tube-DIY say similar to knubie . .?
No, you just linked to the rule I'm referring to. I didn't say knubie's calculation was wrong - I didn't check. It is wrong to consider motor run caps exceptional to any other AC rated cap.
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