The proportional difference is greater because the saturation voltage of
the PA transistors is probably 2.5 volts. That reduces the swing
available. So the swing with 14 supply is only 10.5. With 12 volt supply
its only 8.5 so the available swing is down to 81%, and since the load
impedance is fixed that means power is down to 65% and that's driving
the PA precisely to clipping. The low voltage PA is really voltage
sensitive!
73, Jerry, K0CQ
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