LF: Re: Caps for Class-E amp

["Alan Melia" <alan.melia@btinternet.com>]

Hi Demitris, I am not sure of the types codes but I used 1000v or greater 
rating, the problem often is that the caps are not rated for high pulse 
currents. The best kind of caps that are used are rated for pulse operation 
in switch-mode power supply. Normal caps will not take the current 
pulses.....the individual plates get disconnected from the lead wires.
One of the caps I used has come to hand its a RIFA PHE428 rated 2000v. I 
used this on 36v Class E running about 300W. I believe WIMA make similar 
caps but I am not sure of their type numbers.
Alan
G3NYK

----- Original Message ----- 
From: "Dimitrios Tsifakis" <dtsifakis@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, August 08, 2012 11:03 PM
Subject: LF: Caps for Class-E amp


> 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