LF: Caps for Class-E amp

[Dimitrios Tsifakis <dtsifakis@gmail.com>]

Hello LF group,

I am building a 200 W Class-E transmitter for LF but keep killing the
capacitors in the output circuit (both C1 and C2 according to the
schematic in  Sokal's QST article). I have used a mixture WIMA
polypropylene MKP10, MKP4 and  FKP1 caps and I haven't damaged any FKP
ones so far. Should I not bother with MKP and use only FKP caps or is
there any other type of capacitor what will do the job? I need a
couple of hundred of nanofarads. The voltage rating of the caps I
destroyed was 400 VDC or 250 VAC. I can see that these caps have a
decreasing AC rating as the frequency goes up, but that's what I had
in the junk box at the time...

The mode of failure of these MKP10 0.1 400 VDC caps is interesting
too, they seem to go down in capacitance as the damage progresses.

Any advice is appreciated.

73, Dimitris VK1SV/SV1DET