The L2 is a low power audio amplifier triode. The filament is probably oxide coated to achieve such a low heating power.

The top of the envelope has the identification details. These include the words P.O. Research Station.

Taken from the side of the envelope, the date stamp can be seen as May 1934.

The balloon envelope is 43 mm in diameter and, excluding the B4 base pins, is 88 mm tall.

 
Pin Connections

B4	1	2	3	4
	a	g1	f	f

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	2.0	0.1	150	-3.8	4.0	12,500	1.5

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 02 December 2007 {find valves by name}