The UAF42 is an early all glass valve introduced in 1948 together with the EAF41 and consists of a single diode and a variable μ RF amplifier pentode in a single envelope.
The B8A valves initially appeared in the UK with metal skirts with a locating pip and spigots to cover the evacuation tube. This example retains the metal skirt and locating pip but has the evacuation tube at the top and thus no need for the spigot. Later the metal skirt was replaced with the skirt diameter and pip moulded in the all glass envelope.
By the early 1950s the B8A valves were being phased out in favour of B9A and B7G based valves.
Just under the gettering is the diode anode and below that the screened pentode.
Through the screen can be seen the three wire grids. The anode consists of two small plates joined by a strap - seen just above the skirt.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 55 mm tall.
References: Data-sheet & 1040. Type UAF42 was first introduced in 1948. See also1948 adverts.
