The 1F5G is a battery audio output valve. It is identical electrically to the 1F4, the difference being that the 1F4 is on a UX5 base.

The anode load for use in single ended circuits is 16,000 Ohms. A cathode resistor value is not given.

The classic envelope is 43 mm in diameter and, excluding the IO base pins, is 96 mm tall.

References: Datasheet & ¹⁰⁴³. Type 1F5G was first introduced^¶ in 1936.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	-	f+	a	g2	g1	-	f-	-

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout	D
	2.0	0.12	135	135	-4.5	8.0	2.4	0.2M	1.7	0.31	5%

Thanks to Frank Philipse for supplying the above PDF datasheet