Driver/Input tubes

The idea isn't very complicated. Amplification typically needs to be done in stages. If you try to get too much gain out of a single stage, you end up with inadequate output, distortion, non-linearity, noise and other problems.

The music sources (CD player, tuner, tape deck, etc.) you hook up to your amp provide only line level voltages, usually about 2 volts max. That's not enough to drive the output tubes directly -- they typically want several times the voltage supplied by the line level input.

Hence, one uses an interim stage with small signal tubes to boost the input level to that needed by the output tubes. (For the term "driver", think in terms of pushing along -- driving cattle -- as opposed to operating a car.)

The mentioned tubes are also dual triodes that are either used in differential connection or split the signal onto positive and negative for push-pull operation.

Good point about the phase inversion. I believe the more common method is to use the 12AX7 for amplification and the 12AT7 for splitting the signal into the push/pull components. I haven't messed with the insides of Jolidas much so not sure if they follow that convention.

What point about phase inversion? I do understand the concept of the signal level boosting my preamp does, but wondered why 2 similar tube pairs, 12AX7 and the lower gain 12AT7 are utilized in the power amp...I think I did read someplace about signal splitting...so we're close!