The 1H6G is a directly heated double diode triode from the days of the battery valve receiver. The 1B5L is the same valve but on a UX6 base.

The valve would have functioned as detector and first audio amplifier. The second diode would have been available as an AGC rectifier for superhet receivers.

The classic envelope is 36 mm in diameter and, excluding the IO base pins, is 86 mm tall.

References: Datasheet & ¹⁰⁴³. Type 1H6G was first introduced^¶ in 1937.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	-	f+	a	a(d2)	a(d1)	g1	f-	-

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	2.0	0.06	135	-3	0.8	35,000	0.58

Thanks to Frank Philipse for supplying the above PDF datasheet