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Old 6th November 2007, 05:42 PM   #1
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Default Film capacitors for decoupling

Hi!

On schematic for preamp (EF83-ECC88) i'm making at the moment are two pairs of 10u and 0.1u (both film, non-polar) decoupling caps, connected from B+ (310V) to the ground.


I'm wondering if i can parallel 10u cap with 250V versions which are easy to get.
I know i could use lytic instead, but i want this preamp to be exactly like original so i will use film caps for decoupling.

Can anyone explain me why are film caps better for this application?
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Old 6th November 2007, 07:00 PM   #2
kmtang is offline kmtang  Canada
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Try it out and judge by yourself.

Johnny
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Old 6th November 2007, 07:12 PM   #3
SY is offline SY  United States
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A 250V cap across a 310V rail is NOT a good idea! Use a 400V or higher rating.

The advantage of film caps for decoupling is their superior high frequency performance. The frequency at which they start to look inductive is orders of magnitude higher than an electrolytic.
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Old 6th November 2007, 07:42 PM   #4
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SY is correct. If sourcing a film part of suitable value is difficult, use a 'lytic, and bypass it with a film part, whose value is 10% of the 'lytic. Bypassing 'lytics with film parts significantly reduces ESR and ESL.
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Old 6th November 2007, 08:02 PM   #5
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Quote:
Originally posted by kmtang
Try it out and judge by yourself.

Johnny

Quote:
Originally posted by SY

I wil try film vs lytic and SS vs tube regulated PSU.


A 250V cap across a 310V rail is NOT a good idea! Use a 400V or higher rating.

The advantage of film caps for decoupling is their superior high frequency performance. The frequency at which they start to look inductive is orders of magnitude higher than an electrolytic.
Ok, so i really can't cut corners here..

Thanks!
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