Re: Pentode gm wired as a triode



Ian Iveson wrote:

Flipper said:

The inputs to a tube are voltages and the output is current. This is
why it's called a transconductance device.

For a triode the first voltage input is the grid, the second voltage
input is the plate, the summing junction is the cathode, and one can
find the transfer characteristics for each input in the tube's
data*** with the first, and most popular, being a set of curves
showing the effect of the plate input voltage on output current when
the grid input voltage is held constant with the second being a set
of
curves showing the effect of grid input voltage on output current
when
the plate input voltage is held constant.

If we then run the current output through a resistor so that it
generates a voltage signal in phase opposition to the grid, and if
that phase opposite signal, representing a portion of the output, is
then applied to the plate input, it sums at the cathode negatively
with the grid signal and, so, is referred to as negative feedback.

"Finally, it is possible by contrivance and notional reconfiguration
of inputs and outputs to get *anything* to fit the canonical
diagram. This is true not only of triodes but also of resistors,
ducks, the colour blue and the man in the moon. In these cases the
feedback is a function of the contrivance, and not a property of the
duck or the triode. No real property applies equally to all things,
obviously. All cows are black at night.

"I am serious about looking at a book, honestly. It would be a
revelation for anyone able to follow the maths."


ipso facto, case closed.

Hardly. Your argument equally applies to a resistor, or anything else
in the universe. And you haven't closed a loop anyway...you need to
reduce your logic such that your system has only one input (hence the
"back" in "feedback"). Patrick has realised that, hence the
blah-de-blah about stuff like field effects.

What I have made very clear is that I am using the term feedback in
the strict, engineering sense. Some know what I mean, and others can't
be bothered to find out. There is no shortage of elementary texts on
the subject of control systems engineering. Seriously, check one out.

No reason for me to think you or Patrick ever will.

Once again, this internal feedback mumbo jumbo confuses an issue that
is otherwise quite straightforward. We got the answer right without
it. Engineering theory is intended to be useful, not to mystify.

Ian

If ya can't see the difference between a resistor and a triode
your'e a real fuckin dumb fuck for sure.

Patrick Turner.
.

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