In message , Ian Iveson
writes
"Patrick Turner" wrote

In the case of a 300B, and all triodes, there is already an
internal electrostatic NFB loop.

What you call feedback is a matter of definition, not physics or god
or nature.

The usual definition would not normally include your idea of how a
triode works. If the output is taken from the anode, then the output
is a result of a self-regulating system with the point of dynamic
equilibrium modified by the Vgk input. There is no feedback to the
*input* (Vgk), which is why it would not fall under the usual
definition of a feedback control system.

According to your thinking, a resistor, or a pot, would equally be a
feedback control system.

Until you get your head around this point, the rest is not worth
comment.

cheers, Ian



Yes there is NFB. Consider this: The grid of the triode is fed from a
non-zero source impedance. The signal at the anode is inverted. There
is capacitance between the anode and the grid.

OK?

So we have internal capacitive NFB, which rolls of the gain at high
frequencies. Typical, and expected triode behaviour.

So what would you call it?
--
Chris Morriss