How to calculate output power for a push pull AB1 guitar amp

[Ptron]

...the "effective" load impedance (Zo') is the combined affects of OT reflected impedance (Zoo/4) and the combinational loading of the tube(s) itself (also called 'load factor'):

Zo = Zoo/4 <---purely an OT and speaker function

% = (rp/(rp+Zo))^2 <---'load factor', a tube & OT function

Zo' = Zo * %

...thus the "full" original equation is:

Po = (gm*Vg)^2 * (rp/(rp+Zo))^2 * Zo

...which simplifies to:

Po = Zo' * (gm*Vg)^2

...by letting Zo' = Zo * (rp/(rp+Zo))^2

...and, remember that the Vg signal is assumed to be an RMS-value, not a peak value!

Google isn't giving me much help in finding information on combinational loading. Anyone care to explain what it is? Wild guess: Is it the load that the oppsite tube puts on the working one?

Is this the reason that if you take a 50W P-P pair amp and simply parrallel two tubes to make a quad, it will still be a 50W amp? If you ignore the combinational loading part of the equation: double the tubes, double the transconductance, double the power.

[Old Tele man]

...go visit PENTODE PRESS and look at the 'Vacuum Tube Archeology' postings...there's an article explaining what "loading factor" is and which old college textbook you can find the source information in.

[Ptron]

Is this the reason that if you take a 50W P-P pair amp and simply parrallel two tubes to make a quad, it will still be a 50W amp? If you ignore the combinational loading part of the equation: double the tubes, double the transconductance, double the power.

Well, I'm trying to do the numbers but I must be screwing something up. I'm getting ~69W with two EL34s, Vg=36V-pk. Then when I add a pair of tubes ( double gm, halve Rp) I get 244W!