How much interaction accures between the two halves of a double triode?

[Tubis]

How much interaction accures between the two halves of a double triode?
For an example:

In the left circuit, the amplitude generated from the second half of the triode
is much greater than from the first half. Will this greater amplitude create an internal negative feedback within the tube and lower the amplitude generated from the first half to it reaches status quo?

In the right circuit the first half of the triod generates much greater amplitude than the second. Will the first tubes amplitude jump to the second and
lower that stages amplitude even further?
And can the jump in worst case be so great that it totaly cancels out the second stage phase and make the second
stage have a smaller copy of the first stage phase?

Is it possible to calculate the interaction if the anwers to my questions are yes?

[Steve Conner]

The main interaction is the capacitance between the two plates. This should be specified in the tube datasheet, so you can calculate its effect on your circuit.

In both the circuits you posted, the two triodes are successive stages. In other words, the plate of stage 1 is connected to the grid of stage 2, so the stray capacitance between plates just adds to the plate-to-grid capacitance of the second triode. So, it just looks like more Miller capacitance, rolling off the high end.

The real fun starts when you add another tube stage somewhere else, between two triodes in the same bottle. Then the feedback between the two sections is positive and can cause instability. As long as you stick to the rule of keeping successive stages in the same bottle, the feedback is always negative, and the worst that can happen is loss of treble.

[Tubis]

So there is only capacitance bleeding?
No electromagnetic field bleeding thru space?

[Steve Conner]

Electromagnetic field bleeding through space is the same thing as capacitance.

And mutual inductance too, of course, but due to the high impedances in tube preamp circuits, the "magnetic" part of the field, and the inductive couplings that it causes, can be ignored.