[Alex]

Hello.

This issue is slightly off-topic since it is related to tube superheterodyne
radio rather than tube amplifiers.

A known fact is that in a heptode (or pentagrid) frequency converter (mixer)
there exists a coupling between the first grid and the third grid via a so
called space charge. The space charge (electron cloud) under the third grid
(RF signal) pulsates due to the cathode current modulation by the first grid
(local oscillator).

The phenomenon depends upon which grid is used for LO, and which is for the
signal. It also depends on the rube type. It also varies with AGC negative
voltage.

Could anyone on this forum recommend a book / refer to a book where such
coupling is analysed in detail with quantative figures, maths, plots,
practical recommendations, etc.

Thanks in advance,
Alex