Message-ID: <4B0D312E.5080203@sighthound.demon.co.uk>
Date: Wed, 25 Nov 2009 13:29:18 +0000
From: John P-G <gm4slv@sighthound.demon.co.uk>
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Subject: Re: LF: Class E pa
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LF, Roger,

Mal gave some insightful comments re: Class-E

I have also used a class-E amp on 500kHz,and I echo all the comments 
about careful choice of FET and of the output tuning/loading to get the 
correct drain waveform.

My usual contraption uses a single IRF150 (a TO3 cased 100V/18A SMPSU 
device) at 100W output. I've never had any trouble with this device 
expiring, even when running on a 30V PSU, with the peak drain/source 
volts flirting dangereously close to the 100V device limit.

I've run a beacon occasionally overnight, at 100W (200mW ERP from my 
small vertical) and come down in the morning to find the antenna in 
disarray, capacity wires flapping in the wind, SWR sky high, and the 
IRF150 still going strong (if a little warm!)

For antenna adjustment I wind the variac down to get 10W output and can 
happily keep a carrier on while I visit the antenna field and adjust the 
atu (including disconnecting the feeder to insert a reflected power meter).

I did try a pair of IRF640 in parallel in Class-E and acheived 200W. 
They weren't quite so forgiving though, and expired in a shower of 
sparks when I accidentally removed the antenna connection....


John
GM4SLV