• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Push-pull output impedance

I want to calculate the output impedance of a class AB push-pull output stage from the speaker's point of view(without GNF loop). I have estimated rp for the output tubes but I'm not sure what to use for RL, the class A load for each tube? the class B load? the combined plate to plate load? Do I halve the impedance because there are two tubes? I just need a little direction here.

Then do I divide by the impedance ratio of the transformer to get the output impedance at the speaker?

Forgive me if this was covered in another thread, but I could not find it.
 
You can calculate for low-level signal around the idle operating point. Rp can be derived from the tube characteristics at Vp and Ip. The two tubes in push-pull are connected in series with the primary. Rsec = (2 x Rp)/T^2
At high level the output impedance will be a nonlinear function of drive level, but I don't think it will differ much from the low-level value.