A single EL34 operated in Class A gives an output of 11 W at 10% distortion with a line voltage of 265 V.
A special technique has been devised to enable the EL34 to operate at high anode voltages whilst retaining a single-ended octal-based construction. The valve envelope is made completely of glass, with a conventional pressed glass foot, and clamped into a metal ring which holds together the glass and the plastic material of the octal base. The stiff wire leads projecting from the glass envelope line up exactly with the pinning in the octal base; during manufacture these leads are passed straight inside the octal pins, without crossing over outside the bulb, and so the risk of flash-over is very much reduced. For high voltage operation the valveholder of course must also be able to withstand the high tension.
Such a small valve as the EL34, dissipating a large amount of power at the anode and screen grid as heat, needs reasonable ventilation. It should be mounted vertically, and the air should be able to circulate freely. The distance between two EL34's should be at least 40 mm, and the distance from the cabinet and other components at least 30 mm. Wire-wound resistors, mains transformer, and rectifier should not be in the immediate vicinity.
Since the material on the front page of this leaflet was prepared for the April issue of 'Wireless World', further work has been carried out on the distributed load operation of two EL34's in a push-pull output stage. Hitherto this kind of output stage has not received much attention, though one version of the circuit was discussed by D. T. N. Williamson and P. J. Walker in 'Amplifiers and Superlatives', Wireless World, September 1952. (In the U.S.A. this type of output stage is referred to as ultra-linear'.)