Re: Why are "engineers" so poorly educated?

In article <ysCdnRxD4pBzfbjanZ2dnUVZ_oKhnZ2d@xxxxxxxxxxx>,
"Arny Krueger" <arnyk@xxxxxxxxxx> wrote:

"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.

Actually the modulator in the 50B was operated at a relatively low power
level relative to the modulator in the 50A. The 50B was modulated at a
relatively low level and used push pull class B RF power amplifiers to
boost the carrier power to the 50 kW level, while the 50A used high
level plate modulation of the final RF stage, hence considerably more
audio power was required. The 50A however was only capable of about 70%
modulation, while the 50B was designed to do 100% modulation.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/
.

Relevant Pages

  • Re: Modulation Inductor?
    ... How do you measure peak envelope power? ... power output capability of the amplifier? ... When you modulate AM with voice to 100% positive modulation, the peak ... When you modulate AM with a sine wave to 100% positive modulation, ...
    (rec.radio.amateur.homebrew)
  • 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. ...
    (rec.audio.tubes)
  • Re: Old Xmtrs, "Ancient Modulation" and Modern Amps
    ... >> Nobody used a linear amplifier for AM in amateur radio circles. ... to run the transmitter with no modulation, and run it into a ... has lower input power than a linear amplifier that is truly linear. ...
    (rec.radio.amateur.boatanchors)
  • Re: Class C engineering question
    ... to the RF amplifier increase when modulation is applied? ... Remember, too, that the half-power rule is for sinewave modulation. ... output is four times the unmodulated power, for half the time, and zero ... modulation is coming through a transformer, ...
    (rec.radio.amateur.homebrew)
  • 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)