The circuit is a 2 stage FET amp. I need to know how to figure out Av2 if C4 is open. I know how to get AV1, gm*R3, but can't figure out Av2. With Vin = 10mV rms. Any help would be appreciated.

Thanks.

 

The effective mid-band drain load for the second stage would be R6 in parallel with RL - call it Rp.

With C4 open the second stage gain would be

Av=-gm*Rp/(1+gm*R5)