The SP-16 Green spot was introduced by Cosmos in 1928 as a general purpose valve for HF or LF and for transformer coupled circuits.
See also the SP-18 Red AF and Sp-18 Blue for Resistance/Capacitance coupled circuits.
The shortpath construction employed a flattened cylinder as the anode. Thus the electrodes were closer together than in other valves of the time.
Through the glass can be seen the green identification spot and the writing etched into the glass. The BVA logo and no BBC logo suggests a post 1927 made valve.
The top view showing the anode shape and the filament wires.
The grid in shortpath valves has a single support close to one side of the anode. This can be seen in the top left of the image.
The grid extends beyond the lower end of the anode. The two thick filament supports are also seen as is the BVA logo and other lettering.
The balloon envelope is 43 mm in diameter, and excluding the B4 base pins is 96 mm tall.
References: Data-sheet & 1043. Type SP-16 Green was first introduced in 1928. See also1928 adverts.
