In message , Nick Gorham
writes
Chris Morriss wrote:

In message , Nick
Gorham writes

Stewart Pinkerton wrote:

*All* amps use feedback, but some don't use *global* feedback, leading
to a common claim about 'zero feedback' valve amps.


Been thinking about this, where is the feedback in a triode, with a
NiCad between its cathode and ground ?

I use this in my phono stage, and I can't for the life of me, see
any feedback.

-- Nick

The low internal impedance in a triode is because of the internal
feedback between the anode and the grid. Although the feedback
mechanism is obvious at high frequencies (Miller effect) the varying
voltage on the anode couples to the grid as an NFB mechanism even at LF.

Yes I can see that, didn't think of it a feedback, but you are right.
Don't quite see how that leads to Miller, but thats probably my lack of
understanding. Should be able to fix that given time :-)


The A-G capacitance, together with the source impedance of the signal
feeding the grid create a Miller (or Blumlein) integrator.

--
Chris Morriss