i_m_ken:
IIRC, AD uses a preamp tube at power tube position, then dump lots of the output to return it to line level. it's like:
modelling preamp -> tube power amp (preamp tube) -> resistive load -> solid state power amp (where the power rating thing comes in) -> speaker.
IMHO it IS power tube distortion BUT it's the wrong type of tube AND the signal is MASSIVELY attenuated AND there is no proper output transformer AND no tube-speaker interaction. the missing parts (power and output transformer, more tubes) are what makes a tube amp expensive. still, it has very decent "tube character" for a hybrid amp, IMHO better than marshall's AVTX.
suckasucks:
as for the valbee, i happen to see it's electronic block diagram, it appears to use quite some transistors to achieve the high again function. even for the clean channel, there is a transistor boost stage and a transistor powerd EQ. maybe that is what contribute to its clean tone and break up.