[R-390] C553

[Larry H]

Charles, I've known about the killer C553 cap for a long time and have installed high voltage reliable caps in there to hopefully save my filters from destruction.  What cap would you recommend for C553?

David,  your idea about a current limiting device in that circuit got me wondering - what about the most basic one we use all the time?  A tiny little solder in fuse of some reasonable value.  Any drawback to using a fuse?

Regards, Larry


On Tuesday, August 5, 2014 4:44 PM, David Wise <David_Wise at Phoenix.com> wrote:
 


Thanks, Charles, I stand corrected.  I totally would not have expected that, because the voltage across the cap is basically constant.  I guess even tiny changes can make a difference in some circumstances.

The only 1KV C0G part at Mouser is SV14AA103KAR, at $6.69 each.
There are several film/foil models for less.

I wouldn't be surprised if my current limiter idea had the same problem, but I don't have the wherewithal to set it up and measure it.

Best Regards,
Dave Wise

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Charles Steinmetz
Sent: Tuesday, August 05, 2014 4:29 PM
To: 390 list
Subject: Re: [R-390] C553

David wrote:

>For C553, TC, VC, DF, DA, even IR and piezoelectricity, are 
>irrelevant if held to real-world limits.

Not so.  I was easily able to see additional IMD on the spectrum 
analyzer when I replaced C553 with a Class II ceramic (e.g., Z5U or 
X7R).  A Class I ceramic (C0G/NP0) should solve that 
problem.  Film-and-foil caps also do not generate measurably 
increased distortion.  So, if one decides to use a ceramic for C553, 
one is well advised to use a C0G/NP0 type.  They're harder to find, 
but they're out there (e.g., AVX SV01AA103JAA).

Best regards,

Charles



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