>
> The Collins 30S-1 (4CX1000A), and several larger commercial amps
>(4CX5000, 4cx10000) for which I have schematics, incorporate a loading
>sensor which has a (capacitive) voltage divider with one end connected
>directly to the plate. These units also all happen to connect the screen
>directly to ground.
>
> The Collins 30L-1 (811A's x4) uses the Plate-Grid capacitance of one of
>the tubes along with smaller than typical grid bypass caps plus a small
>RFC back the the grid return to implement this same type of divider.
>
> Two questions:
> Could the Plate-Screen capacitance of a Tetrode (4CX250, 4CX1000A,
>etc.) be employed in a similar fashion if the screen was bypassed with an
>appropriate value capacitor.
>
** If the screen is bypassed, there is no signal potential on the screen
- and it can not be used for such. Unless a grid-driven 4cx5k or 4cx10k
has their internal feedback-C neutralized, they will not be very stable.
I've been there, and it cost me some hair.
> and...
>
> Would the resulting signal be exactly in phase with the Plate voltage
>so it could additionally be used in a phase discriminator style tuning
>indicator?
>
** The slam-dunk tuning-indicator for an grid driven AB1-tetrode is the
screen-I meter. Once the ZSAC is adjusted, and the max grid-current is
almost zero, the Screen-I meter tells us everything we need to know.
cheerz, Marv.
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