Re: Why are "engineers" so poorly educated?


"John Byrns" <byrnsj@xxxxxxxxxxxxx> wrote in message
news:byrnsj-A65639.08242729102007@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <4725d70e@xxxxxxxxxxxxxxxxx>, keithr <keith@xxxxxxxxxxxxxx>
wrote:

To state the bleedin' obvious, a class AB amplifier is not a class A
amplifier. You would bias it rather differently to a pure class A job.
Class AB is a clever hack or kludge to get over the deficiencies of both
class A (dreadful efficiency and excess heat) and class B (crossover
distortion). Class B is the only one that scales to high power, and as
the
crossover distortion is a fixed amount, it's significance diminishes as
the
power level rises.

It is not obvious that only the class B amplifier "scales to high
power". For example the RCA 50A AM broadcast transmitter used a SE
class A modulator that I estimate was good for an audio power output of
at least 16 kW, not a lot, but not to shabby either, for a class A
amplifier.

True, but not all that strange, given the era. The 50B dates back to 1926
or 1927, which was actually before push-pull operation was generally known
to exist. People built SE amplifiers because they didn't know any better at
the time!

Also, the 50B used Heising modulation, ostensibly to avoid the use of
another high-tech innovation, being the modulation transformer.


.

Relevant Pages

  • Rebuttal to Richard Clarks comments on my Chapter 19A
    ... RF power window at the input of the pi-network, ... plate, and the slope of the load line. ... the amplifier in this condition will later be shown to be 50 ohms. ...
    (rec.radio.amateur.antenna)
  • Re: Rebuttal to Richard Clarks comments on my Chapter 19A
    ... RF power window at the input of the pi-network, resistance RLP at the ... plate, and the slope of the load line. ... the amplifier in this condition will later be shown to be 50 ohms. ...
    (rec.radio.amateur.antenna)
  • Re: Why are "engineers" so poorly educated?
    ... Class B is the only one that scales to high power, ... It is not obvious that only the class B amplifier "scales to high ... another high-tech innovation, being the modulation transformer. ... Actually the modulator in the 50B was operated at a relatively low power ...
    (rec.audio.tubes)
  • Re: why it isnt so important, but still has meaning (long!).
    ... > amp, it may in some cases lead to problems, of which some are outlined ... > Let's assume an amplifier stage with BJTs in class AB such as we find ... > Good, negative loop feedback linearizes the amplifier's properties, so ... > Then we have the physical limitations of the power supply. ...
    (rec.audio.opinion)
  • DF: why it isnt so important, but still has meaning (long!).
    ... we have an ideal voltage ... amp, it may in some cases lead to problems, of which some are outlined ... Let's assume an amplifier stage with BJTs in class AB such as we find ... Then we have the physical limitations of the power supply. ...
    (rec.audio.opinion)