First, it wasn't an assertion... more like a "I wonder if...." On to the wave form thing...... Every Class A/B audio amp must be push pull. It cannot be any other way. All push pull amps have some sort of phase inverter to which provides near identical, yet mirror image waveforms to the output. This is the same on solid state, tube, or hybrid amps. They all have phase inverters. The adjustment (circuit design) of the phase inverter determines the output symmetry, regardless of the hardware that does the output. Tubes like the 12AX7 run class A. There is no reason at all to run a 12AX7 itself as a push pull design. Class A amplifiers are biased such that the output is set between shutoff and saturation... at the midpoint, and both top and bottom halves of the signal waveform are conducted. Why two triodes then? Just to have another one to use for whatever. So, the 12AX7 is best used as a class A amp, in the signal path (if its used as an amplifier), and the phase inversion and symmetry (or not) is taken care of immediately before the output section.