In article .com,
Peter Wieck wrote:
On Oct 23, 8:51 pm, John Byrns wrote:
In article . com,
Multi-grid wrote:
***Class A operating conditions do not permit the output device to
cease conducting.***
Precisely, that is why when the operating conditions of a class AB
amplifier are restricted by limiting the applied input voltage the
amplifier is able to put out class A power at a level that is lower than
the maximum available class AB power.
John, with respect:
Andre is out of his depth on this one.
Peter, I know you are obsessed with Andre, but this is not about Andre,
it is about Multi-grid's silly statement that a class AB amplifier can't
put out a limited amount of "class A power". Multi-grid is confusing
the definition of a PP amplifier's class with it's ability to deliver
some amount of power, less than rated output, without either output tube
cutting off. It has been common usage for as long as I can remember to
call this "class A power" because at this power level both output tubes
are conducting over the full 360 degree cycle, as in a class A
amplifier. An amplifiers class is determined by the operation of the
tubes at the rated power output, however in the case of a class AB
amplifier, a lesser amount of "class A power" is available.
To illustrate how silly Multigrid's claim is, consider a class AB
amplifier with a rated output of 50 Watts in class AB. Further suppose
this amplifier is capable of putting out 15 Watts without either output
tube cutting off, 15 Watts of what Andre, and many other famous
amplifier designers, call "class A power". Now we all agree that this
is a class AB amplifier, but suppose we connect a suitable network of
Zener and ordinary diodes across the primary of the output transformer
which clamp the maximum output voltage at the level necessary to produce
an output of 15 Watts. Has this amplifier now become a class A
amplifier simply because we have placed this clamp circuit across the
primary of the output transformer? If we test it with our sine wave
generator and oscilloscope we are going to conclude that it is a class A
amplifier because both tubes are still conducting over the full 360
degree cycle at the point of clipping. I leave the implications of this
experiment for the student to consider.
Regards,
John Byrns
--
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