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Old 29th June 2012, 10:10 PM   #1
Einric is online now Einric  United States
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Default Simple P-P Capacitors

Looking to order my simple pp parts.
C3 calls for a .47uf 100V mylar capacitor.

Would a Film & Foil 400V be acceptable?
Is there any difference pro or con?

Like this maybe?

Thanks
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Old 29th June 2012, 11:58 PM   #2
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You can always use a higher voltage rated cap in place of a lower voltage rated cap no problem, just be aware the the higher voltage rated caps are physically larger, so convince yourself that they will fit before pulling the trigger.

The size thing gets really different when trying to substitute a film cap in place of an electrolytic, not the case here, but for fun compare a 22uf electro vs a 22uf film.

The Daytons also come in 250V rating; they will be smaller than the 400V parts and more likely to fit.
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Old 30th June 2012, 05:51 AM   #3
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This is what you want & is what George includes in the kit;

ECQ-E1474KF Panasonic Electronic Components | EF1474-ND | DigiKey

The lead spacing on the board is only 7.5mm so a higher voltage axial cap would be tough to fit.
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Old 30th June 2012, 02:20 PM   #4
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What about the square package MKT caps?
CAP FILM 0.47UF 100VDC RADIAL
They are in stock and have a 7.5mm spacing.
I am planning on doing all of my parts on the bottom with only the small resistors on top.
This may give me a little more flexibility with physical part sizes.
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Old 30th June 2012, 02:23 PM   #5
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C101 and C201 values are stated as "depends on OPT".
I will be using the CXPP25-MS-7.6K so what should I use?
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Old 30th June 2012, 08:13 PM   #6
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Default Does Tubelab give you nominal cap values in the parts list?

Quote:
Originally Posted by Einric View Post
C101 and C201 values are stated as "depends on OPT".
I will be using the CXPP25-MS-7.6K so what should I use?
Those are feedback compensation caps for the feedback resistors. They are typically dialed in by installing the nominal value to start, getting the amp functional, then looking at a square wave (typically 10Khz) with a scope. The cap values can be tweaked a bit to get the cleanest looking square wave under test. The final cap value is dependent on a few circuit parameters, specifically the output transformer.

You could pick up a couple of caps a little larger and smaller than the nominal values so you are ready to go once the amp is up and running, or just install the nominal values if you don't have access to a scope.

You want to end up with the leading edge of the square wave to be fairly sharp, with no ringing/overshoot. Typically, when you get the cap value dialed in for no ringing/overshoot, the leading edge will be slightly rounded; that's about the best you can do. A rounded leading edge shows that the high frequency response is lacking, and overshoot/ringing can sound sub-optimal (sometimes "harsh" highs) as well. So you can play with these cap values and let your ears decide what's best.

Last edited by boywonder; 30th June 2012 at 08:18 PM.
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Old 30th June 2012, 09:19 PM   #7
Einric is online now Einric  United States
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There is no stated nominal value on the parts list.
Where should I begin?
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Old 1st July 2012, 12:18 AM   #8
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Quote:
Originally Posted by Einric View Post
There is no stated nominal value on the parts list.
Where should I begin?

Read this thread:

feedback compensation capacitor on the Tubelab SPP

I think that the builder in the thread above used your exact transformers, so you are in luck!
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Old 1st July 2012, 12:21 AM   #9
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Cool, Thanks, I'll check it out.
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Old 1st July 2012, 12:52 AM   #10
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So it looks like 270pf is a good place to start.

Would 500V be sufficient or would I be better off going with the 1KV?
I can get tighter tolerances in the 500V so I don't have to order a pile of them to match up.
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