I understand that rectifiers create DC from AC - and I know the rectifier section of a tube amp feeds the output tubes. But what exactly happens in the phase inverter mode? is it getting ac current and turning it into DC? if it is DC, why do we need two matched output tubes? Speakers are feed an "AC" signal - are they not? I am confused then, Why do we need a device that changes AC to DC in order to power output tubes and then speakers? I just don't get it - can you help me out?