Quote:
Originally Posted by Synchrodyne
Another way of looking at this is, since the current through both valves is the same, to neglect for the time being the non-vacuum interface between the two and to see the grid of the upper valve as an earthed screen (and one that does not partition the electron flow) between the lower valve grid and the upper valve anode. Now we have a pentode-like situation where the output swing is determined by the combination of the mutual conductance of the lower valve and the load resistance of the upper valve.
Cheers,
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I agree with this entirely and for the valve case it is a pretty good way to look at it, as it is very much like a screen grid pentode but partitioned into two vacuum spaces (if separate triodes) with two sources of electron emission with plate currents that are equal.
In the same way you can inject a signal into the screen grid of a pentode you can also do this with the grid of the upper valve in cascode which can make a handy "port" for some applications.