The 25A6G is an audio output pentode that was designed for single ended use in universal sets. The heater is designed for series connection across the mains supply, and the anode ratings reflect the low HT available when no mains transformer is available.

The Type 43 is identical electrically but fitted with a UX6 base cap.

The classic envelope is 43 mm in diameter and, excluding the IO base pins, is 101 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type 25A6G was first introduced^¶ in 1936.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	g2	g1	-	h	k

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout	D
	25	0.3	160	120	-18	36	12	42,000	2.4	2.2	10%

Thanks to Frank Philipse for supplying the above PDF datasheet

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