The 12Q7GT double diode triode 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 name. The triode is at the top with the diodes sitting below on the common cathode. One diode is formed from the plates forming the box. These plates are folded over at the top to enclose the box. The second diode is formed from the two vertical rods within the diode anode box.
The triode anode has an oval working space. The cathode tube remains uncoated between the diodes and the triode.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 71 mm tall.
References: Datasheet, 1040 & 1043. Type 12Q7GT was first introduced in 1947.