On Fri, 06 Jun 2008 20:58:13 -0500, Cecil Moore wrote:

Antonio Vernucci wrote:
Usually, when a transmitter is tuned for maximum output power,
efficiency results to be higher than 50% (typically 60% for class-B,
70% for class-C). This would seem to contradict the above cited fact
that, under maximum power transfer condition, efficiency is 50%.

The maximum power transfer theorem only applies to
linear sources. What is the linear source impedance
of a class-C amp?

The source resistance appearing at the output of either a Class B or C amplifier is R = E/I, where E is the
peak voltage at the output terminals and I is the peak current at the output. Or RMS values can also be used.
Since E/I is simply a ratio, R is also a ratio. And we know that a ratio cannot dissipate power, or turn
electrical energy into heat, thus the output resistance R is non-dissipative. I have made many measurements
that prove this. It is also the reason why reflected power does not dissipate in the tubes, because it never
reaches the tubes. The reflected power simply causes a mismatch to the source, causing the source to deliver
less power than it would if there were no mismatch. The input at the pi-network in the xmtr is non-linear, but
the fly-wheel effect of the network tank isolates the input from the output, resulting in a linear condition
appearing at the output. Except for a very slight deviation from a sine wave due to a small amount of harmonic
content, the voltage E and current I at the output are essentially a sine wave, which one can easily prove
with a good oscilloscope, proving the output to be linear. I'm speaking for tube rigs with pi-network tanks,
not for solid-state rigs.

I nearly forgot. The only dissipation in the amp tube(s) is due to the filament-to-plate current as the
electrons bombard the plate. The efficiency is determined by the ratio of the DC input power to the RF output
power. The maximum power is delivered when the load resistance equals the output resistance R of the source.
But since resistance R is non-dissipative it is not a factor in determining efficiency. The only factors in
determining efficiency are the RF output power and the dissipation in the tube caused by the electrons
striking the plate. The non-dissipative output resistance is the reason Class B and C amps can have an
efficiency greater than 50 percent. If the output resistance were dissipative it would be the determining
factor in efficiency, which could never be greater than 50 percent if the load resistance was equal to the the
output resistance.

A report of my measurements will soon be available in Reflections 3, from measurements taken since those
reported in Chapter 19 of Reflections 2.

Cecil, if I send you a copy of the new chapter that has the report of my newer measurements do you have any
way to make it available to the guys on this thread?

Walt, W2DU