This PM2HL looks to be a replacement type. It was found in its original box and was priced at 4/9 (four shillings and nine pence). This battery triode is a small signal amplifier of low impedance and gain.

Flat on to the bright anode the grid, and notched support rods, can be seen to extend beyond the 22 x 12 x 5 mm anode. Note the coil springs above the top mica to tension the hot filament.

The anode in close-up shows the spacial relationship between the twin inverted V (coated?) filament and the grid. The wide spacing makes for a low mutual conductance.

The balloon envelope is 40 mm in diameter and, excluding the B4 base pins, is 83 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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