Re: qcx 40 low power high heat high current #40m

Mike Easterbrook

Had a similar experience with one of my 20m builds - I was continuing to get increased power as I removed turns from LPF but at a certain point (I don't  remember exactly where) but current increased from abt 400 to 900 mA, key shaping went awry, PA efficiency dropped  & lots of heat generated. I would look to increase LPF inductance by squeezing turns or if necessary increasing turns. I concluded that something in the PA/Q6 area was going into self-oscillation. Reducing supply volts (below 12) also helped. Never managed to pinpoint any further as didn't dare running more than a few secs under the high current condition. Sorry for the vague reporting - can't decipher my notes now!  
Hope this may help. 
Mike 9M2LXM

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