I have a model of a vacuum tube pentode. What I'd like to do is get a graph of the change in dynamic impedance looking into the anode at a constant anode voltage as the screen potential is varied. So I guess I'd ground the grid and need some way to sink the varying current as the screen potential changes. And some way to measure the dv/di at the plate.
Does anyone know a way to automate something like this in LTSpice?