Chris Morriss said:

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?

Miller effect.


Of course, and the Miller effect has an effect because of............?
(Here's a clue, the words negative, feed and back may just come into it)


;-))))))))))))))

--
Sander de Waal
" SOA of a KT88? Sufficient. "