The CV3889 (EL41) is an early all glass output pentode. Mullard describe the EL41 as an output pentode rated for 9 watts anode dissipation, and intended primarily for use in AC mains operated equipment. They state that the EL41 should only be used with self-bias or semi-automatic bias.
The anode looking straight at the grid line. The copper supports of the control grid are surmounted by heat radiating fins.
Looking along the grid axis. The side flanges are placed in the centre of the working face for greatest effect. The three wire grids indicate a true pentode.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 68 mm tall.
References: Datasheet & 1040. Type CV3889 was first introduced in 1948.