I am currently studying for the CETa exam through ETA-i. In the amplifier section Vacuum tubes are discused and so are the subsequent calculations for biasing such antiquity

I understand so far that the input signal is introduced via the grid, if I am interpreting the diagram for a VT correctly, and that the plates, I assume, are much like the collector and emitter of the BJT that I am far more familiar with.( Very easy to calculate the voltage-divider bias)

What is not clear though, is how he goes about deriving the values for the different biasing components to produce the gain he desires. For example, he is using values from a dynamic transfer graph, with curves for various loads, corresponding to a grid voltage and a plate voltage. However, his values for plate current do not seem to match the intersection of the load resistance with the plate voltage. It's quite confusing on how it's presented, and of course it's only a study guide, so the explanation is brief. Basically I can follow what he is doing, but I dont know why he is doing it that way. I looked in the different online books we have here, (very impressive by the way) but could find nothing on VT's.

If anybody would happen to have some guidance to add, or a link to a good online resource for understanding Vacuum tubes and biasing more completely I would greatly appreciate it, thank you.