[TowerTalk] silver mica power capacity

[Grant Saviers]

I built the "Field Day Special" (by W7EL) 20m antenna which uses 330pf 
500vdc silver mica capacitors in each lead at the feedpoint to match 
50ohm coax.  It seems to work fine, so now I'd like to upgrade the power 
handling to full limit.    How do I size silver micas for the voltage, 
current and power dissipation for full power?  I've got the 500vdc rated 
CDE CM/CD series in most values at 500v rating (new 1kv ones are 
pricey)  so some sort of series/parallel arrangement is what I expect is 
needed.

20m and 40m versions are planned.

 From various CDE pdf's it seems the ESR for <1000pf is around 0.005 
ohms at 14MHz, and DF of 0.009 at 1MHz.  Another pub has the max current 
at 5MHz 85 deg C for 330pf as 1.5a and for 680pf as 2.3a which by my 
understanding (not sure about it) is much less than pure ESR losses i.e. 
(5a^2 * 0.005ohms = .125 watts).  I would guess that a silver mica could 
dissipate 1/8 watt without distress, but don't understand what might 
limit current capacity per the CDE data.  I probably need to series caps 
for 1000vdc to provide some SWR margin at full power.

Insight and advice appreciated.

Grant KZ1W