[RodB]

Now you're getting into theory. Phase inverters typically have a gain of one. This is to make the signal at the plate equal to the signal at the cathode, but 180 degrees out of phase. You'll notice the plate signal is fed to one output tube and the cathode signal (thus called cathode follower) is fed to the other output tube. This is the push and pull, one tube is conducting the other is cut off, then vice versa. Now, that said, the signal amplitude at the plate should be pretty close to the grid signal and cathode signal amplitude.