(Primarily in tube amps) Splits the signal into two "mirror" halves to drive the power tubes in a "push-pull" configuration.
The behavior of an amplifier is defined by how it manipulates electrons through these basic components: guitar amplifier electronics basic theory pdf
But theory alone is cold. The real knowledge comes when you replace a cathode capacitor and hear the bass response double. It comes when you measure the voltage drop across a plate resistor and realize the math worked. (Primarily in tube amps) Splits the signal into