The EF42 miniature high slope RF pentode is of an all glass construction and dates from 1947 and was first seen at the Olympia show that year. Mullard specify this device for use as an RF or an IF amplifier.
Thus all glass example has the base groove typical of Philips manufacture, and the envelope carries the words Made in Holland. Our other EF42 has the earlier construction of a metal skirt, with locating pip, over the all glass envelope. The first B8A valves featured a metal locating spigot.
The UF42 has identical characteristics but is fitted with a 100 mA heater for use in series heater chains.
Little to be seen within.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 52 mm tall.
References: Data-sheet & 1040. Type EF42 was first introduced in 1947.