The CV878 (commercially the 7A8) octode frequency changer or mixer was designed self oscillating front ends of broadcast superhet receivers.
In 1948 with American valves in short supply Brimar ran a series of adverts to show how these valves could be replaced with UK types that were obtainable - from Brimar.
The inner coating hides the internal structure but there are glimpses of the wire grids near the base. The location pip is on the skirt and the spigot has a key - all to ensure the correct orientation of the valve entering the socket.
The dome has an octagonal border with the 7A8 Type designation within. Thus the commercial and the CV specification are identical. The style of lettering suggests that this is a Sylvania valve.
The wide glass tube envelope is 29 mm in diameter, and excluding the B8B base pins is 56 mm tall.
