[R-390] Seeking to understand grid voltage at mixers

[Barry Scott]

Note that this is in reference to the R-390/URR but is applicable to
the R-390A/URR as well.

The manual states that when the function switch is in STAND BY, the
grids of the three mixers should have a negative voltage within a
certain range and I'm trying to understand where that voltage is
coming from.

In STAND BY, B+ is removed from the plate circuits of the mixers so
there's nothing but the 1M grid (leak?) resistors and the cathode
circuit.

Considering the case of just the third (PTO) mixer, its cathode is
tied to ground through various elements of Z702.

Given all this, for the third mixer in STAND BY, is the negative
voltage at the grid a product of electrons that are drawn to the more
positive grid due to the much higher resistance to ground than the
cathode's circuit?

Thanks,
Barry - N4BUQ