The L2 is a low power audio amplifier triode. The filament is oxide coated to achieve a low heating power.
The early production valves had a balloon envelope this shouldered design came later.
The anode is ribber for dimensional stability of the thin nickel sheet. The vertical rod is the support for the filament tension spring. The identification is etched into the dome and is Radio Record and L2.
Top view: the oxide coated inverted V filament is held in the flat hook of the tension spring. The grid looks to be close wound.
The classic envelope is 38 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
References: Data-sheet & 1040. Type L2 was first introduced in 1931. See also1931 adverts.
