I don't see any indication for the pentode amplification factor?
I am curious how the pentode amplification ... compares to a 12AX7?
mu = gm * rp
Therefore:
mu = 0.001 * 2000000 = 2000
As you can see, pentodes have colossal mu! It's also very difficult to determine accurately, so it's not a very useful metric which is why datasheets don't quote it.
Further, the formula we use to determine in-circuit gain recognizes that the external plate load resistor forms a voltage-divider with the internal plate resistance of the tube. Amplification = Mu x [Rl / (Ra + Rl)]
For a Triode "Rl" (the external plate load resistor) is usually bigger than the internal plate resistance of the tube. But the pentode's internal resistance is almost always higher than the plate load resistor, so we don't use that formula to estimate in-circuit gain of a pentode. That's because if you put 100kΩ in parallel with a 2MΩ internal plate resistance, the total resistance is "nearly 100kΩ."
So as
Merlin noted here, we calculate Pentode Gain as "Gm x Plate-Load." Within this framework, there are approaches that seek to maximize Gm and different-approaches that use lower-Gm and a larger plate load resistor. Gm for the tube is controlled by choice of screen & bias voltages, with higher idle current leading to higher Gm for the tube.
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