This valve is a co-axial triode similar to the VT90 in general construction but lacks the clear route for forced air cooling. The ceramic envelope indicates a high working temperature. Perhaps the central anode was cooled by conduction and this was designed for aircraft use. The CV15 was certainly designed for conduction cooling.
The grid connection and inside of the end can be seen the metal evacuation tube seal.
The heater/cathode connections. The + sign shows that this could be a directly heated type with a tungsten or throiated tungsten filament. At 1.2 Volts it draws 6.0 Amps and is almost certainly directly heated in the same way as the CV15.
The design looks to be a high temperature device.
The co-axial envelope is 16 mm in diameter, and excluding the base pins is 97 mm tall.
Updated April 11, 2019. shape:co-axial construction:disc.seal.(ceramic) type:triode base: pin: