Tom W8JI wrote:
>>OK, probably a stupid question. Are we sure that the
>>tuning point with minimum input capacitance is actually
>>tuned to 50MHz, and not 100MHz, with the stage acting as a
> A doubler with that conduction angle should have well under
> 10% efficiency, but I suppose it is possible the 6 meter
> tank is hitting two or more frequencies at once. That was
> one thing that crossed my mind.
That was my thought at first - harmonic load phase angles (or a load
line if one exists) could have a big effect in a hard driven amplifier.
Another thought (much easier in a picture). Plot a grph of Po/Pi for the
high efficiency/high load resistance case. The line goes up, then bends
over and the gradient decreases with increasing Pi. Superimpose a plot
for the low efficiency tuning point - the line goes up at a lower angle,
but is straighter and goes on for longer. There will be a point where
the two lines cross, same Pi, same Po, one gives better linearity, the
other better efficiency.
Doug - can you run some numbers for the low anode/high grid current
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