The PM2HL battery triode was designed for detector service in broadcast receivers. The two volt filament was for operation from an accumulator, which is typical of radio valves from the 1930s

The classic envelope is 32 mm in diameter and, excluding the B4 base pins, is 82 mm tall.

References: Datasheet & ¹⁰⁴³. Type PM2HL was first introduced^¶ in 1938.

 
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	135	-1.5	2.2	21,500	1.4

Thanks to Andy Cowley for supplying the above PDF datasheet

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