The 13SPA is a screened amplifier HF pentode. Two versions exist 13-SPA with external metal paint and this exhibit with a clear glass bulb.
The control grid is taken to the top cap for maximum isolation between input and output circuits. This valve was used in RF and IF stages of domestic radio receivers with a common heater chain and used for Universal AC/DC sets.
The screening is formed by the perforated cylinder and discs top and bottom. The anode is a cylinder.
The rod originating from the top of the pinch connects to the anode as does the rod at the lower end of the pinch. The connection between the outer screen and the lower disc can be seen in the centre of the image. The grid wires can be seen between the screen and lower disc.
Here the anode cylinder can be seen just inside the screen.
The classic envelope is 38 mm in diameter and, excluding the B7 base pins, is 97 mm tall.
References: Data-sheet. Type 13SPA was first introduced in 1934. See also1934 adverts.