Thanks Stefan, I will buy a few  using FKP1 caps, hopefully that will
do the trick.

> After all tests i have done with high RF power and caps, i can say that the
> FKP-1 caps perform excellent. They are cheap and easy available, at least
> here. I heared much about the silver mica caps but can't find them anywhere.
>
> I'm using FKP-1 caps in a 1 kW clöass E PA running at 80V DC, without any
> problems!

What is the VDC rating of the FKP1 caps in your 1 kW PA?

>>   I need a
>> couple of hundred of nanofarads.
>
> So the supply voltage is 12V?

Output impedance is about 1.4 ohm. I have designed it to produce 50 W
at 12 V and of course 200 W at 24V.  I work in multiples of 12 V as I
normally use big SLA batteries to power my equipment. The FET is a
monster IXYS 500V/55A FET which should be bombproof. In theory I
should get ~800 W from a 48 V supply but unless I solve that capacitor
problem, I won't even try to test it at that voltage.

I do know that things are probably simpler if I select a higher
voltage supply as that will increase the output impedance and make
life a bit easier on the poor capacitors. But I do want to be able to
operate it out in the field and not carry half a truck worth of
batteries :-)

 In any case, I don't want to go more than 200 W as I am scared of the
voltage developed across my loading coil (currently about 12 mH or ~10
kohm XL).

73, Dimitris VK1SV/SV1DET