As per the schematic T1 is the input transform, T2 is output A, T3 is output B, and T4 is the Monitor Out. Best way to be sure is to open meter bridge and measure for continuity between the XLR output the the Blue or Green transformer wire, I forget the polarity if pin 2 or 3 go to Blue or Green but so easy to
figure out....just put meter in beep mode.