The DET22 is a UHF disc seal triode developed during WWII and this M-OV valve carries the GEC branding that was used on valves intended for professional equipment.
A grounded grid configuration would allow for a two cavity mechanical design. This valve is rated at 600 MHz but its extended maximum frequency of 4 GHz made it a natural choice for microwave designs. The anode dissipation is 10 Watts.
The copper anode connects to the ring on the right and terminates in a flat face that is placed very close to the grid. The grid connects to the lower ring and consists of many fine wires stretched across a hole in the flat metal plate. These grid wires can be seen in the image.
The coaxial connections to the heater and cathode and the underside of the grid plate. This plate can be seen to have the fine wires attached across the width of the plate. The cathode cylinder has a flat top and only this top surface is coated with emissive material.
The planar envelope is 15 mm in diameter and 59 mm long.
References: Data-sheet & 1005. Type DET22 was first introduced in 1945.