The CV1240 is a modified form of the PT15 transmitting pentode. The PT15 was used in airborne transmitters.
The CV1240 was originally called the NT65A indicating a UK Navy valve.
The valve is directly heated with an oxide coated filament. The presence of the screw top cap points to a design of the early 1930's. Grid 3, the suppressor grid, is connected to the metal base. The locating pin indicates that the base would be of the bayonet type.
Here the anode is seen side on to the camera. The extra heat sinking offered by the supports and flanges is located in the centre of the working face.
The screw top-cap and top mica. Note the projections that form an interference fit to the envelope.
The base, base pins and locating pip. The base insulator is ceramic and about 5 mm thick. Strength is required in the base and pins when a bayonet holder is in use.
The lower mica is also a tight fit to the glass tube. The anode can be seen to be pressed metal, normally nickel.
The wide glass tube envelope is 52 mm in diameter, and excluding the base pins is 176 mm tall.
