The X79 is a triode hexode frequency changer or mixer. The triode control grid is connected internally to the oscillator injection grid (g3) of the hexode.
The GEC brand label of the M-OV company. The GEC brand was reserved for professional applications.
The triode section is sited above the top mica and runs at right angles to the electrodes of the hexode.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 49 mm tall.
References: Data-sheet & 1040. Type X79 was first introduced in 1950. See also1950 adverts.
