"Richard Harrison" bravely wrote to "All" (01 Mar 05 08:29:27)
--- on the heady topic of " Say what you mean."

RH From: (Richard Harrison)
RH Xref: aeinews rec.radio.amateur.antenna:26189

RH The Class A amplifier gets all its power from the d-c supply and it is
RH constant, signal or no signal. With signal power output, some of the
RH power in exits to the load.

Let's look at it from the dynamic point of view. When there is no
signal the circumstances are as you describe. When the signal swing
turns the device nearly OFF there is a maximum voltage across the
device but the current is a minimum or close to zero.

Conversely when the signal swings in the opposite polarity the device
turns ON hard but the voltage is at a minimum or near zero too. In
either case the "ideal" device dissipates no extra power because the
two products are always zero. In fact the power difference is
always zero, so there is no reason for the device to cool.

However, no device is ideal, it has losses, and generates harmonics.
If the rectification is such that the average current decreases then
the device will cool. There is a gotcha however, because the harmonics
rob power from the desired output.


RH I`ll use Cecil, W5DXP`s argument. Energy must be conserved. Energy in
RH equals energy out. If some goes to a load it does not stay within the
RH amplifier to make feat.

As you said, if the amplifier dissipates 100W when idle and it can
drive 100W into a load then the power source will still supply 100W
when so doing, of course being an ideal device and neglecting all
other losses. It is easy to test by paralleling a substantial
capacitance and measuring the supply current before the cap. The
current should remain the same or rise only very slightly.


RH Asimov also wrote:
RH "---linear source not operating Class A?"

RH I`ll give an example. The Class B amplifier is biased near current
RH cut-off. Current is near zero when the signal is. Yet, output can
RH favorably vie with that from a Class A amplifier for purity. I learned
RH that nearly 60 years ago when I built my first 6N7 phonograph
RH amplifier.

Class B is hardly linear if it only amplifies 1/2 of the sinewave.
Time for our periodic 10 year review. g

A*s*i*m*o*v

.... That's a cute trick.