"Fred Nachbaur" wrote

...
Another notion I've intended to try out (and indeed will, one of
these
days) is to use the cathode coupling (short-tail pair) and augment
the
signal to the "off" phase with a voltage divider from plate of the
"on"
phase to grid. This would seem to give a less distorted signal
than
taking it from the screen grid.

By making this variable, the amount of asymmetry can be varied to
either
side. This might actually be useful for blues harp or acoustic
guitar
players, since it appears that acoustic feedback can be reduced
this way.

Confused Ian again...

you only identify two legs of the divider so your scheme seems
ambiguous to me.

Do you mean top to anode, bottom to same grid, and middle to
opposite grid. Or top to anode, bottom to ground, and middle to
opposite grid? Or maybe even top to anode, bottom to opposite
anode, and middle to opposite grid?

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. More interestingly
because of the difference between the series and parallel-derived
alternatives, when it comes to maintaining correct phase
relationship across the whole bandwidth.

Also wondering which sources of distortion will tend to cancel, and
which will augment. For example with the series derivation from
opposite screen, will the nonlinear blip in screen current at low Va
result in a signal that will counter or reinforce the simultaneous
drop in Ia?

Dunno if that made sense...I know what I mean...

cheers, Ian