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Old 14th February 2013, 07:55 PM   #1
krm76 is offline krm76  Spain
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Default Capacitors voltage rating

Hi,

I'd like to change some of the capacitors from my chinese valve phono stage and althought I have found most of them, there some that do not match the voltage rating.

My question is if the capacitors need to work close to their voltage rating level in order to be efficient.

Thank you
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Old 12th April 2013, 04:24 PM   #2
RNMarsh is offline RNMarsh  United States
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If they are not electrolytics, then the answere is No.
But for long life use a film capacitor that is rated as high voltage or higher than the power supply (B+).

If they are electrolytics then the answere is sometimes you get a little better performance running them closer to caps max Dc rating.

Thx-RNMarsh
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Old 12th April 2013, 04:39 PM   #3
jcx is online now jcx  United States
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but for safety, long life caps should be derated - operated with actual in circuit V at some fraction of their rated V

used to be that for Al electrolytics recommended factor was ~ 80%

actual circuit conditions also need allowance for AC line variations, transformer regulation - easily another 20-30%

depending on topology, a coupling cap could see full supply V if a heater dies, and amp load goes to zero too - so would have to apply all factors together
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Old 12th April 2013, 05:02 PM   #4
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When Nelson mentioned the elna silk caps i tested several -- for coupling where you have to use an electrolytic the higher voltage caps had lower THD
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Old 12th April 2013, 05:22 PM   #5
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by jackinnj View Post
When Nelson mentioned the elna silk caps i tested several -- for coupling where you have to use an electrolytic the higher voltage caps had lower THD

This has been generally true of all make and brands of electrolytics and was discussed a few decades ago.

Another maybe forgotten parameter which indirectly affects the performance is the higher temp rated electrolytics (105C) are better still over same value/voltage.

Good to keep putting this info out every so aften. Or it gets lost and has to get rediscovered/invented.

Thx-RNmarsh
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Old 13th April 2013, 11:41 AM   #6
AndrewT is offline AndrewT  Scotland
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The DC voltage PLUS the transient spikes will sometimes exceed the Voltage rating of the capacitor.
It is these excursions that exceed rating that use up the life of the capacitor.

If the cap can never have a transient spike applied to it then it can be run at 100% of voltage rating.

If a cap is regularly exposed to transient spikes then expect it to have a shorter life no matter what DC voltage is applied during normal running.

My opinion based on what I read.
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