On Mon, 16 Jun 2008 03:32:23 GMT, Owen Duffy wrote:

The analysis is waiting for me to build the
analytical equations for the negative feedback due to cathode
degeneration in a grounded grid configuration.

Hi Owen,

Consult the work of H.W. Bode taken from his lectures at Bell Labs ca.
1939, and then rendered into text as:
Network Analysis and Feedback Amplifier Design,
Chapter IV Mathematical Definition of Feedback
4.2 Return Voltage and Reduction in Effect of Tube Variations p 46
It attends specifically (grounded grid triode) what you call out
above.

In a nutshell, Output (or Input) Z can be tailored by what is called
the "noise gain" of an amplifier. In today's parlance, that is that
portion of Open loop gain that is fed back to the input to create what
is called closed loop gain ("noise gain" is simply the difference when
all gains are expressed as dB). The higher the "noise gain" the lower
the output Z (or higher the input Z) compared to the native (open
loop) Z. There are a host of other characteristics improvements that
flow from this same boon offered by "noise gain" (dynamic range, noise
rejection, linearity, CMRR, PSRR, and so on).

This shorthand can be found expanded in discussion in
5.5 Effect of Feedback on Input and Output Impedances of
Amplifiers
bullets 1. through 4. but it serves the reader to really stick with
the first 4 chapters to gain the proficiency to tackle the remaining
15 as the text is heavily cross-referential.

The general formula can be found at:
5.11 Exact Formula for External Gain with Feedback (5-30)

Bode was not simply a chalk-and-talk theorist wholly ignorant of the
practical realities as are evidenced in several chapter headings:
Chapter VII Stability and Physical Realizability

Chapter IX Physical Representation of Driving Point Impedance
Functions

Chapter XI Physical Representation of transfer Impedance Functions

Chapter XIII General Restrictions on Physical Network
Characterizations

Ultimately, it takes very little reading applied to the conventional
designs found in Amateur class amplifiers to discover there is really
very, very little modification of amplifier characteristics offered
through negative feedback design (it costs too much). In fact, I
would say none whatever - hence the heavy filtering at the outputs and
the customers' universal acceptance of barely mediocre performance. It
might be said that every transmitter owned by hams is a museum of
1930s performance. And for those who mistake the feedback of
stabilization (barely found in those same cheap designs) - this is not
negative feedback, it is compensation. It too has scant effect on
tailoring (reducing/increasing) impedances.

As I am undoubtedly the only copy holder of this book in this group,
access can be obtained through:

http://books.google.com/books?client...G=Search+Books
which will provide a surplus of leads, if not the exact title. Some
links might provide a pdf, others full access, yet others limited
access, and most have links to copies in the market place.

Given the usual confusion over what constitutes a Conjugate match
(when most argue an Impedance match in its place) says discussion of
"Efficiency and maximum power transfer" without more rigorous
resources fails to even reach the level of tepid conjecture.

Bottom line is the source presents a real resistance and no appeal to
ratios, linearity, load lines, fly-wheels, or partial cycles is
necessary to arrive at a definitive value (which, to this point has
been notably absent in the face of obviously localized heat and loss).
There is plenty of discussion of what it is NOT, but none seem to know
what it IS. That the typical Amateur amplifier source Z is
demonstrable is embarrassment enough to this shortfall of expertise.
(The pile of theories, books and formulas merely support the obvious,
not replace it.)

73's
Richard Clark, KB7QHC