The idea of push pull is that two valves are better than one if you want serious power delivery. Transformer coupling can be used - see later - but the use of a valve phase splitter is often found. In the push pull circuit the two valves must work 180 degrees out of phase with each other and to do this the input signal has to be split into two. There are a number of variations of the push-pull circuit. This is quite a common variety.

Assume a signal from an earlier AF amplifying stage has reached the grid of the triode phase splitter via C1. R2 and R4 are of equal value and so the current through the valve is divided equally between them (ignoring the presence of the low value R3, there to bias the cathode). C2 and C3 are outputs from the valve: each going to one or other of the output valve grids. Note the presence of R5 and R6 disposed across the two outputs with a centre-tapping to the cathodes of the output pair via R7. C4 is the common bypass capacitor for both cathodes. The gain of the phase splitting stage is unity, hence the need for an earlier AF amplifying stage. The outputs at cathode and anode of the phase splitter are of course approximately equal but of opposite phase to each other. A little thought shows why this is:

Imagine a positive-going signal at the grid of the phase splitter. The valve conducts harder as the signal goes more positive, resulting in a decrease of voltage at the anode but an increase in exact proportion at the cathode.