The X63 heptode mixer is typical of the 1930/1940s frequency changer. The triode oscillator is formed between the cathode and g2 acting as an anode, and has to generate a peak to peak voltage of 25 Volts. The mixer is screened by G3 and G5 with the signal injected into the oscillating electron stream at the top cap g4.
The envelope has the etched identification lozenge typical of an M-OV product. Unlike our other X63 this has a clear envelope.
The MArconi paper label.
From the top the inner structure can be seen. The grids are circular. The screen grids are strapped together as can be seen on the right and the between these to grids on the left can be seen the connection to the top cap for the signal. Grid two is a plain un-notched rod either side of the cathode and this forms the oscillator anode.
The classic envelope is 36 mm in diameter and, excluding the IO base pins, is 98 mm tall.
References: Data-sheet, 1040 & 1043. Type X63 was first introduced in 1937.