The HL2 is a dull emitter battery triode. It was designed as a detector in broadcast receivers, in the early 1930s. This exhibit is made by Lissen and the gettering obscures most of the construction.
The anode is left bright in this low power valve.
The identification is etched into the envelope dome. The made in England is at the top and the Lissen logo beneath the HL2.
A close view of the top of the anode. The grid wires pass flat across the face of the anode and inside can be seen the white of the oxide coated filament
The balloon envelope is 42 mm in diameter and, excluding the B4 base pins, is 93 mm tall.
References: Data-sheet & 1040 Type HL2 was first introduced in 1931. See also1931 adverts.
