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.
Philco's message to try and maintain the replacement business.
The doubling of the letters is due to the reflected image from the gettering inside the glass being seen as well as the etching itself.
Above the base it is possible to see the mass of wire grids within the anode.
The wide glass tube envelope is 29 mm in diameter, and excluding the B8B base pins is 56 mm tall.
Reference: Data-sheet, 1040 & 1043. Type 7A8 was first introduced in 1938. See also1938 adverts.
