Need Help to Determine Quiescent Current in Class AB Output Stage
However I am not able to find equation for quiescent collector current
of NPN transistor in output stage due to my limited knowledge of
circuit analysis.

There isn't really a recommended value. For some who require extremely low distortion, the collector current will be significantly higher and for the rest of us mortals with an  &quot;adjuster&quot; (aka small screwdriver) we'll combine R3, R18 and R9 into a pot and adjust it so that it sounds about right.