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 the same valve on a UX6 base.
The brimar identification. Through the darkened glass the line of grids can be seen thus this is a true pentode.
The classic envelope is 44 mm in diameter, and excluding the IO base pins is 100 mm tall.
References: Datasheet & 1040. Type 25A6G was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated November 27, 2014.