More capacitance for tube rectified filter caps?

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honkyjonk
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More capacitance for tube rectified filter caps?

Post by honkyjonk » Mon Apr 28, 2014 8:40 am

Hey folks,

This is in regard to the 'ol RodC modification of an Akai M8 amp. I'm replacing the multicap filter cap (2X20uF 350V) What I have in the drawer is a couple 33uF 450V caps. These should be fine right?
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Darlington Pair
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Re: More capacitance for tube rectified filter caps?

Post by Darlington Pair » Mon Apr 28, 2014 9:38 am

honkyjonk wrote:Hey folks,

This is in regard to the 'ol RodC modification of an Akai M8 amp. I'm replacing the multicap filter cap (2X20uF 350V) What I have in the drawer is a couple 33uF 450V caps. These should be fine right?
That's totally fine.

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Post by ashcat_lt » Thu May 01, 2014 10:01 am

First of all, a smallish 33uF could be the same value as a big 20uF and they could both still be in tolerance.

Second, bigger capacitance means lower cutoff which means better ripple rejection.

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floid
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Post by floid » Thu May 01, 2014 6:12 pm

tube rectifier datasheets typically list a max filter cap value, determined by the cap's current draw - pull too much and you fry the tube. a maximum value's tolerance range may put a particular example beyond what the tube can handle.
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Post by Matt C. » Thu May 01, 2014 7:40 pm

floid wrote:tube rectifier datasheets typically list a max filter cap value, determined by the cap's current draw - pull too much and you fry the tube. a maximum value's tolerance range may put a particular example beyond what the tube can handle.
this is what I thought too, but now that I'm looking at a bunch of tube rectifier datasheets, they're all listing capacitor sizes for "typical operation", not maximums. so, I guess I'm not sure what the scoop is. I'd imagine a huge capacitor could cause problems but I bet increasing from 20uf to 33uf would be a big deal.

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Post by Jim Williams » Fri May 02, 2014 7:47 am

If a tube rectifier can't handle in rush current, pull it out and solder a couple of IN4007 diodes in it's place.

I would use 470 uf at 400 volts, if they would fit.
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Post by themagicmanmdt » Mon May 05, 2014 11:18 pm

hush, jim, you'll ruin the magic
Jim Williams wrote:If a tube rectifier can't handle in rush current, pull it out and solder a couple of IN4007 diodes in it's place.

I would use 470 uf at 400 volts, if they would fit.
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Post by Orpheus » Thu May 15, 2014 7:50 pm

I'm going to concur with Mr Williams. I freaking hate tube rectifiers

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