The X30 is a heptode frequency changer (USA = pentagrid converter) with a 300 mA heater for use on sets for Ac or DC mains. The introduction of the X30 was in 1934.
The anode cylinder side view looking along the line of grid supports.
The top mica with the row of grid supports. The grid closest to the cathode is the oscillator control grid. The position of g2 is taken by two plain rods that act as the oscillator anode. G3 and G5 are strapped together and form the screening grids. Connected to the top cap is g4 - the signal input grid.
The lower mica: the cathode tube is cylindrical and oxide coated.
The classic envelope is 44 mm in diameter, and excluding the B7 base pins is 117 mm tall.
References: Data-sheet, 1040 & 1043. Type X30 was first introduced in 1934. See also1934 adverts.