The CV1645 is a low impedance amplifier triode that was based on the M-OV experimental Type E133. The GPO or General Post Office had responsibility for all of the public telephone network in the UK and the CV data-sheet indicates that this CV valve was for GPO use.
The anode side view also showing the support rods to the left that hold the filament tension springs and top end of the grid. The pip on the base shell is for location in the bayonet base.
The two inverted V filament are connected in parallel. The grid is wound on a single support that is bent in a semi-circle at the top. The filament wire is not coated indicating a thoriated tungsten filament. When connected it glows bright orange - confirming that it is thoriated tungsten.
A closer view of the electrodes. This is clearly an early design as all supports are secured in the pinch and no mica or ceramic sheets are used to hold the electrodes in their correct relative positions.
The top of the anode showing the grid winding, the filaments and the filament tension springs.
The envelope also carries the M-OV style logo and the Type designation of VT38. As different agencies used the same VT and two digit Type the CV register distinguished them by calling the RAF transmitting valves VTxx, the GPO valves POVTxx and the American Government vacuum tubes as VT-xx.
The balloon envelope is 55 mm in diameter, and excluding the UV base pins is 114 mm tall.
