The VT46 RAF transmitting valve is a directly heated audio output valve with a commercial equivalent of the PT25H. After 1941 when the CV register commenced it became the CV1046.
The wording says made in England by the MO Valve Co Ltd. GEC. The anode is held to the support struts by tape welded on to both.
The M-OV lozenge with Type designation within. VT stands for Valve Transmitting and is a UK RAF designation that pre-dates the 1941 introduction of the CV classification.
The B5 base is ceramic. This would offer better resistance to damp at altitude and in tropical environments than Bakelite.
The anode and grids seen through the dome of the envelope. The plate to the top left of the image is the getter holder. The filament tension springs can be seen above the three concentric grids. Pentodes on a B5 base would have the suppressor grid taken to the centre point of the filament. The grids are geld in position by two mica sections. The wires attached to the screen grid supports are in turn taken to a glass rod. The rigidity of the wires held in the glass keeps the micas apart. The glass rod itself is positioned with wires that are welded to the anode supports.
The grids with oxide coated filament strands passing through them. The filament wire is held to the tension springs by small spring wire.
The Air Ministry logo and crown are etched into the side of the envelope.
The balloon envelope is 66 mm in diameter, and excluding the B5 base pins is 150 mm tall.
References: Data-sheet & 1043. Type VT46 was first introduced in 1934.