The X14 is a heptode frequency changer designed for battery superhet radio receiver use. The local oscillator is formed between the cathode and grid 2. Grid 1 being the oscillator control grid. The pulsating electron flow is screened by Grid 3 from the oscillator and grid 5 from the anode. In this screened space is the mixer control grid g4. For maximum isolation between oscillator and signal circuits the mixer control grid is taken to the top cap.
The Osram paper label.
As a low power device the anode has been left bright. The inner grids pass flat across the filament, whereas the outer grids move closer to circular.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 87 mm tall.
References: Datasheet, 1040 & 1043. Type X14 was first introduced in 1940.