The 6A5G is an audio output triode. It is indirectly heated and with a load of 2,500Ω will deliver 3.75 Watts at 5% total harmonic distortion. The construction is as two units connected in parallel internally.
The data sheet describes the 6A5G as suitable for the same applications as the 6A3 (UX4 base) and 6B4G (IO base). In both cases the valve is the American answer to the classic PX4.
In push-pull a pair of 6A5G were rated at 10 Watts when released in 1937.
The two joined triode sections. The top of the grid can be seen in the tops of the triodes.
The pinch and lower mica. On the base is the maker's name.
The IO base pins.
Thanks to Mark Mallison for sending the images.
The classic envelope is mm in diameter and, excluding the IO base pins, is mm tall.
Reference: Datasheet. Type 6A5G was first introduced in 1937.