The clean channel is solid state but does run through the phase inverter and power tubes, so it's actually pretty warm sounding.The drive channel is tube and runs through a 12ax7 with a 12axt phase inverter too.
The clean channel is solid state...it does not use a pre-amp tube but does utilize the power amp section. One 12ax7 is a preamp tube and the other is the phase inverter so the drive channel is all tube, whereas the clean is a solid state preamp.