The X143 is an all glass triode heptode frequency changer for radio reception. The central locating spigot is also the connection for the cathode, grid 5 and the internal mesh screen.
The oscillator triode was designed to produce 14 Volts peak to peak feed for the mixer section. The heptode portion is vari-μ.
The screen obscures the electrodes.
The base with central locating spigot acting as pin 9.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 62 mm tall.
Reference: Data-sheet & 3002. Type X143 was first introduced in 1949. See also1949 adverts.