I'm replacing the preamp tubes in my DT50 112. I believe one is an input buffer and the other is a phase inverter. I ordered a standard 12ax7 for the input buffer, but I ordered a balanced 12ax7 for the phase inverter. The sockets are labeled V3 and V4 with the power amp tubes labeled V1 and V2. Conventional wisdom would say that V3 is the power inverter because the socket number is next in line to the power tubes. However the only thing I could find online is someone who "thought" the numbering system was different on DT50s. So, does anyone know for sure which socket is the phase inverter? Thx!!