[600MRG] Capacitors

[Larry Molitor]

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