Mesa Subway Blues tube functions

[dilznik]

Hi all,

I got the below diagram from Mesa and it's clear what the power amp tubes and V4 are doing. And V1 actually. Is V3 the main gain stage and what is V2 doing?

 

[JackStraw12]

Is one an effects loop/reverb? I think V2 is the PI, at least that's what it is on my Subway Rocket

 

[Don A]

V3 is the PI.
V2 is a gain stage and FX loop recovery.