The 6Q7G is a double diode triode and was designed for receiver audio use.
The diodes would be for signal and AGC rectification and the triode would act as AGC amplifier or first audio amplifier.
The Brimar logo, BVA logo and Made in England are printed on the base cap.
The triode is at the top of the single cathode tube and the anode plates leave a cylindrical cavity for the grid. Below the centre mica is a box screen with two stout rods passing from the pinch into it. These rods are the diode anodes. Just above the pinch can be seen a horizontal wire. This connects the cathode to the diode screen.
A closer view. The triode grid connects to the top cap.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 100 mm tall.
References: Datasheet, 1040 & 1043. Type 6Q7G was first introduced in 1936.