Re: [SPAM] Re: [BITX20] Higher voltage for Bitx40 Final

K9HZ <bill@...>
 

Did you re-bias the 510s when you changed the PA voltage?  If not, theoretically this could happen if the bias were set right on the edge of class “C” operation.

 

 

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From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Jerry Gaffke via Groups.Io
Sent: Sunday, February 04, 2018 3:22 PM
To: BITX20@groups.io
Subject: [SPAM] Re: [BITX20] Higher voltage for Bitx40 Final

 

11.5v should be fine, make sure it is still 11.5 when PTT is pressed.
Quiescent IRF510 drain current changing somewhat as they get warm is normal

The drop from 6w to 4w when V+ to the IRF510's is bumped from 12v to 24v is very weird.
Have you tried simply switching the IRF510 V+ between the two with exactly the same setup, same instrumentation?
Hate to say it, but my first guess would be pilot error.

On Sun, Feb 4, 2018 at 01:10 pm, Vic WA4THR wrote:

Just finished building my BitX40 after playing with the circuit for a few weeks. Early tests on mine suggested that using the small booster I have and raising the PA voltage from around 14 to 24 did seem to increase the power by the square of the voltage ratio, so matching these experiences. Admittedly, I was trying to read this on a 450w dummy load meter, and yelling into the mic, s not very accurate. So this past weekend I did get a QRP wattmeter that could read 30w as full scale and get a better idea of how much I am increasing.

However, now when I apply 24v to the final the power output actually drops from 6w to 4w! The only significant cuircuit difference is that I am now running the other 2 power connections (main board and Raduino) through a 7812 regulator, and since it is not getting quite enough to regulate to 12v, it is delivering about 11.5v to those boards, which I assumed was just a bit safer. The voltage booster is not dropping voltage under load, so I am befuddled as to why the power actually drops when I apply the higher voltage. I did recheck the PA bias and raised it up closer to 100ma, but I notice it slowly increases from wherever it is set if I continue to hold the PTT. Any ideas? Perhaps I should short the input to the output of the little 7812 to see if that actually had an effect.

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