The following is taken from a leaflet entitled 'Mullard world series valves for audio equipment' it probably dates from the early 1960s.
Amplifiers which provide a nominal output of some 20 Watts to handle the loudest music, or even higher powers for public address equipment, include an output stage equipped with two EL34's in push-pull.
An interesting method of connecting the push-pull output stage has been used in a Mullard-designed 20 W amplifier.
The screen grids of the EL34's are connected to taps on the primary of the output transformer, so that the operating conditions lie somewhere between those of a triode and those of a pentode. The latter would be where the screen grids are connected to the centre-tap of the output transformer primary winding. Thus the low distortion of the triode is combined with the high sensitivity of a pentode. The valves are said to be operated with distributed load.
Two EL34's in the output stage can yield an output of 20 W at 0.35% total harmonic distortion, or 34 W at 2.5% distortion, with 430 V between each anode and earth.
The maximum anode dissipation of the EL34 is 25 W, and it has the high mutual conductance (μ) of 11 mA/V.
See The new EL34 Audio Pentode