The ac resistance, rp , of the tube describes the opposition the
tube presents to small changes in plate current.
offered by this tube to small changes around point Q is approximately
NOTE: Use the changes
shown in figure 3-4.
If the tube is operating at point Q, (fig. 3-4) and no signal
is applied to the grid, what is the voltage drop across the load
If the grid-bias voltage, Ecc increases to a value so that the
tube is cut off, the voltage drop across RL will be equal to
If you draw the circuit load line on the plate characteristics
graph, at what point will it intersect the plate voltage axis?
Assume that you do not have the characteristic curves for a
certain tube but you know that is has an rp of 9,000 ohms and a gm of
You can calculate that this tube's amplification