[600MRG] Capacitors

[david vanhorn]

Have you looked at X2Y caps from Johanson or similar parts?  Virtually no
self-inductance.  Also balancing between the sections is very close if you
choose to use them as a pair of caps rather than one high Q cap.


On Thu, Oct 5, 2017 at 1:32 PM, Larry Molitor <w7iuv at yahoo.com> wrote:

> First of all thanks to all those who responded.
> My specific application (this time) is receiver bandpass filters. So....
> Size is important.
> Cost is important. With a total cost of the receiver less than $30 it
> makes no sense at all to spend $50 for filter caps.
> Q is more important in a bandpass filter than in a typical low pass
> filter. Caps I've used successfully in TX low pass designs are not
> acceptable in these bandpass designs. The bandpass designs I'm using
> require much higher values of "C" than low pass designs for the same
> frequency. Most, if not all, of the hi-Q caps I've been using for low pass
> filters are simply not available in the higher values of "C" that I need.
> Rudy,
> The old transmit micas are too big. I have a box of them myself but it
> seems like I never bothered to pick up many of the high values. Most are
> less than 1000 pF. One of the few that was marked at 0.03 uF / 1000V, was
> measured and I saw one of the lowest ESR's of anything I have here.
> Marshall,
> ATC caps are great. I've been using them for VHF through microwave for
> decades. Unfortunately the high Q 100B's are not available in the values I
> need. Some of the bigger case sizes are on special order but they don't
> have as high Q. Even so at 4 bux a pop, I'm not going to buy any.
> Brian,
> The Vishay 715P seems to be an obsolete part. At least i cannot find any
> "new" stock. Mouser does stock a number of Vishay parts that may be
> equivalent and the catalog claims decent (but not outstanding) Q. Price and
> size are reasonable so I might be looking at getting some. If you could
> measure the Q/ESR of some of the parts you have, I'd appreciate it.
> Frank,
> Paralleling caps doesn't help the ESR. A cap with half the "C" will have
> approximately twice the ESR. What you do gain is more surface area to
> dissipate the same heat generated. The caps are then cooler to the touch
> and you feel better even though you didn't gain anything except perhaps
> reliability.
> BTW, The more or less common and not too expensive Silver Mica 500VDC caps
> (you know the "kidney bean" jobs) have very good Q/ESR. Unfortunately the
> cost goes up pretty fast with the higher values of "C". They are
> exceptional in low pass designs if you can get the right values. I even
> have a couple at the feedpoint of my 6 meter yagi and they easily handle
> 1500W of JT65 when I run EME.
> Thanks & 73,
> Larry - W7IUV / WH2XGP
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K1FZY (WA4TPW) SK  9/29/37-4/13/15