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 view looking up into the valve from the base. The heater passes through the cathode tube eight times. The control grid is wound on substantial copper supports.
The classic envelope is 45 mm in diameter and, excluding the IO base pins, is 104 mm tall.
References: Datasheet & 1040. Type 25A6G was first introduced in 1936.
Absolute Maximum Operating Conditions¶
Updated February 28, 2013.