The EL33 audio output valve is the little brother of the 18 Watt anode dissipation EL35 and the later 25 Watt EL37 with which it shares pin connections. Mullard describe this valve as a high sensitivity output pentode for use in AC mains equipment. The EL33 could be used in push pull to deliver 8 Watts, but the normal use was in domestic radio receivers as a single ended stage.
Between the top gettering and the mid level internal coating can be seen the anode and tops of the grids.
The fingers of the top mica holding fast to the inside of the envelope shoulder.
The gettering is either side of the top mica and in the clear glass can be seen the tops of the electrodes. Not the most inspired view.
The glass blurs the inside but one strand of the screen grid winding can be seen.
The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 110 mm tall.
References: Data-sheet, 1040 & 1043. Type EL33 was first introduced in 1938. See also1938 adverts.
