[PJC58-Hythe]

While I agree you cannot exceed the total power dissipation of the valve, it is perfectly possible to work it harder for a shorter duty cycle. If we look at the original RCA 6L6 data it shows a total power dissipation of 24W. If we look at the data for Class A1 (fixed bias) we see a max dissipation at peak signal of 375V x 73mA ~ 27W and with zero signal the dissipation is ~ 22W delivering 11.5W of signal output.

Now look at the data for class AB2 push pull we see a max dissipation at peak signal of 400V x 125mA (for one valve) = 50W and with zero signal the dissipation 21.6W (for one valve) with a pair delivering 60W signal output. The valve is effectively over rated by a factor of 2.08.

If you do the efficiency calculation then Class A1 is about 42% and Class AB2 is about 60%. If all things are equal applying this to a 6L6GC capable of 30W dissipation the maximum signal power output would be ~75W