[Alex]

"Patrick Turner" wrote in message
...
It seemed to me the screen current was always only in
ONE direction, ie, electrons flowing into the positive screen supply
as is does at the anode. Conventional current flow is from positive to
negtive. A series diode in the anode circuit pointing into the anode
allows flow. allows averlam
So the diodes placed the way they are shown for g2 would just allow
screen current all the time in one direction and I cannot think why it
would want to flow the other way.

I'm very suspicious of the validity of the claims at that oestex site.

Patrick Turner.

Alex:
The only way the current n the screen grid can reverse is the secondary
emission from the screen grid. For this to happen, the tube shall be a
tetrode with VpVg2 or a pentode with Vg3 Vg2. If g2 has a pronounced and
consistent secondary emission, then Vg2 voltage will tend to rise (jump
because of the diodes) to about 20...50V below the plate (tetrode case) or
below g3 (which is nearly connected to plate in these odd circuits). Thus g2
will be tracking plate with no g2 net current!!!!!

However I do not think one can dependably rely or reliably depend on the
secondary emission from g2.

And of course, if the beamformer plates or g3 is connected to the cathode,
this will not work at all. And majority of the output tubes do have g3 or
beamformers connected to cathode.







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