The EL42 is an audio output pentode of an early all glass design. In single ended Class A an output of 2.5 Watts was to be expected. This was sufficient for most car radio receivers, but a pair in push-pull would generate a respectable 5.5 watts for larger receivers and audio equipment.
The envelope has made in Holland printed on it. The indentation at the junction of the foot and the envelope is characteristic of Philips production.
The EL42 took over from the EL2 and EL32 and was in turn replaced by the EL95 but the EL85 is electrically identical to the EL42.
The end wall of the anode is perforated and inside can be seen the three wire grids.
Made in Holland by Mullard's parent company Philips. It is believed that the style of jointing the pressed glass foot to the main envelope is indicative of Philips production machinery.
The thin glass tube envelope is 20 mm in diameter, and excluding the B8A base pins is 53 mm tall.
References: Datasheet, 3002 & 1040. Type EL42 was first introduced in 1947.