>One further clarification, in grid driven configuration: yes, the screen is
>grounded for r.f. but so is the cathode (less so if a degeneration
>resistor is
>used), so the drive is still applied between the grid and cathode.
>
>If the peak drive voltage exceeds the bias voltage, grid current will flow.
>If not, then grid current will not flow. This happens in grid driven or
>cathode
>driven service. The grid current curves for a TH347 (the tube I have most
>tested) , in cathode driven service, seem to be independent of actual screen
>voltage and plate voltage.
>
** When no drive potential exists between the screen and the grid, the
tetrode acts as a triode. This is why applying DC screen potential to a
g-g tetrode does not increase amplification or reduce the drive
requirement.
>...
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