Yes, Raa is the impedance seen from anode to anode on a push-pull amplifier. It is also called load resistance, plate to plate (aa = anode to anode). See this page...
lower down at the last table. There you see the familiar 3400ohms load resistance giving you 55watts output.
The same load mismatching (1700ohms Anode to anode) can be achieved by setting the speaker output impedance on the amp to 16 ohms and plugging in a 8 ohm speaker (or set at 8 ohms plugging in a 4 ohm speaker)....
but what is the point of this discussion? ??? What do you want to achieve Valie?
