Fred Nachbaur wrote:

(snip)

Interesting experiments, partly because of the problem getting a low
enough source impedance for that opposite grid without causing
distortion and/or wasting too much current through the divider or
voltage across the current-sensing resistor.

My guess is that it would be just 2 Kohms, quite low enough
to drive a properly biased G1.

That's why it's nice (I think) to take it from the anode rather than the
screen. The absolute value of the divider resistors can be made quite
high, since the grid impedance will be very high in class A1. (Such
approaches would probably bomb spectacularly if grid current is drawn.)

Should work OK - I would not expect any G1 current on the
second O/P tube. But I think the B+ would have to be
decoupled to a "totally zero" impedance down to the lowest
frequency of the O/P stage, even below or you might have an
oscillator - I would not care to speculate on the frequency,
somewhere between "motor-boat" and stuck-pig squeal
perhaps!

(snip)

Cheers,

Roger

--
Roger Jones, P.Eng.
Thornhill, Ontario,
Canada.

"Friends don't let friends vote Liberal"