The Western Electric 'Weco' valve came in three sub-types, green spot, as this exhibit, orange spot and red spot. In the UK the valves were made by STC and given the prefix 4 as in this example. However, the box carries the Western Electric name and so this valve was made before the UK factory was sold to ITT and was established separately as STC in 1925.
The filament is given as 0.8 to 1.1 Volts at 0.25 Amps. The anode voltage was quoted as 15 to 30 Volts for the orange spot, and 30 to 60 Volts for the other two types. The green spot was designed as a detector with the grid at -7 to -10 volts. All three types were introduced in 1925, had an rA of 25K Ohms, a mutual conductance of 0.22 mA/V and an amplification factor (μ) of 5.5.
The peanut bas has four stud connections.
In this image it can be seen that the anode is not a fully closed cylinder and within can be seen the grid.
The instruction notice found in the box. It is clear that the filament is designed for a set current.
The thin glass tube envelope is 15 mm in diameter and, excluding the base pins, is 64 mm tall.
Reference: Data-sheet. Type 4215A was first introduced in 1923.