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 mainly clear envelope allows inspection of the electrodes. The bright box under the triode is a screen connected to the cathode.
The diode anodes are a pair of rods within the screen placed either side of the ascending cathode tube.
Here the diode screen can be seen to be closed at the top except for the hole for the cathode tube. The triode anode is shaped to leave a cylindrical space for the grid and cathode.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 100 mm tall.
References: Data-sheet, 1040 & 1043. Type 6Q7G was first introduced in 1936. See also1936 adverts.
