The 12Q7GT double diode triode was designed for receiver use.
The diodes would be for signal and AGC rectification and the triode would act as AGC amplifier or first audio amplifier.
The triode anode has an oval working space. The cathode tube remains uncoated between the diodes and the triode. The diode anodes should be the two vertical rods inside the screening box. However, the wire from the box support passes into the box and possibly connects to the right hand rod.
The Brimar name. The triode is at the top with the diodes sitting below on the common cathode.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 71 mm tall.
References: Data-sheet, 1040 & 1043. Type 12Q7GT was first introduced in 1947. See also1947 adverts.