Hi Piotr,

In an old tube book I found an equation or
rather inequality - upper limit for the
amplification factor allowing to work
without oscillations caused by C(ag) in a
triode (CC) amp:

[...]

Is the equation correct and is the above
really the case, or am I taking something wrong?

I doubt that this formula given is correct for
a single gain stage under consideration and I am
quite sure that when you breadboard your example
(simulating estimated Miller capacitance somehow)
you will find so. Just try it :-)

Tom

--
The large print giveth, the small print taketh away.
- Tom Waits