The CV780 is a 1H5GT is a dry battery diode triode overprinted with the UK Government procurement code. The valve is for receiver use.
In a TRF receiver the diode would provide AM signal demodulation and the high μ triode would be the first audio voltage amplifier.
Here the single strand filament can be seen entering the screening box containing the diode anode. On the protective metal skirt is the pip to guide alignment in the socket. The spigot has a key and the end ball that gets locked in the springs of the socket preventing easy withdrawal - essential in military equipment.
The dome has the Type designation within an octagon border. The Penta logo is on the left.
The wide glass tube envelope is 29 mm in diameter, and excluding the B8B base pins is 54 mm tall.
