vacuum tube long tail pair question

I'm a hobby guitar amp builder who likes learning the circuits as well.The second half of a long tail pair inverter is the grounded grid amplifier.The grid of this section is grounded through a capacitor.I have read this establishes an AC ground to the grid.I guess I'm not getting how that pertains to this circuit.I know a capacitor can bypass AC components of fluctuating DC current around a resistor.I understand most of how this circuit works in a basic way.Exactly what is going on here?Thanks.

As implied, the grounded grid of the long tailed pair must be at AC ground to operate properly. If the grid operates at some DC bias voltage and is thus not directly connected to ground, then the capacitor to ground provides the AC path.

Thanks for the information.