How The SRPP Works
In a nutshell, one triode stands on top of another with a resistor spanning cathode and plate. First, the bottom tube receives the input signal; second, by reacting to that signal, it gives the top tube its drive signal. While this circuit has several topological variations, in all cases the output is taken at the top triode's cathode.
This circuit constitutes a push-pull output stage that happens to comprise its own phase splitter. Consequently, unlike most push-pull circuits, Class A operation is necessary to the SRPP's functioning. As the current flowing through the bottom tube varies, the resistor Rak sees a varying voltage develop across its resistance in response. This variation in voltage is then given either through a capacitor or directly to the top triode's grid, which will conduct a varying amount of current as a result.  Since the load resistance connects in between the top and bottom tubes and ground, it provides a path to absorb the change in current.

Although at idle both triodes draw an equal current flow, in the presence of an input signal the triodes conduct in anti-phase. How is this possible with two tubes in series? Relative to the top tube's cathode, the signal developed across resistor Rak is in anti-phase to the input signal given to the bottom tube's grid. For example, a positive pulse at the bottom tube's grid results in a negative pulse at the top tube's grid. Therefore, the top triode's change in current conduction will be in anti-phase to the bottom triode's change in current conduction; thus, the pulling and the pushing. As the bottom triode pulls the output voltage down, because it is experiencing a greater conduction, the top triode let's go, as it is conducting less. Conversely, as the top triode pulls the output voltage up by conducting more, the bottom triode let's go by conducting less. The load then sees the delta, the difference, in conduction between top and bottom tube.
At idle we know there is zero difference between top and bottom tube current flow, thus no current is delivered into the load resistance. But if a positive pulse is applied to the bottom tube's grid, its current conduction might increase from 10 mA to 15 mA, while the top triode's current conduction decreases from 10 mA to 5 mA because of the bottom tube's greater conduction through resistor Rak, which forces the top tube's grid negative. The difference between these two currents is 10 mA, which is delivered into the load resistance.
What if there is no load resistor? In this case, there will be voltage amplification at the output, but no current variation between tubes, for
there can be no difference in current draw between top and bottom tubes, as there is only one current path through both tubes. The load resistance defines a second current path, which is available to both tubes.
When the top tube conducts more current than the bottom tube, the difference in current flows through the load resistance into the cathode of the top tube.

 SRPP functions like a push-pull amplifier

Push-Pull One More Time
We have just described the push-pull nature of the circuit, but at the risk of boring some readers, let's cover this action one more time in greater detail, as a solid grasp of the push-pull functioning of  the SRPP is needed to make sense of what will follow later.

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