This DET19 from M-OV also carries the pre-CV RAF code of VT61 and an old stores code of 10E/11442.
It is a low power VHF transmitting double triode that would have been used in push pull with a common tuned anode coil connected across the twin top caps. The HT would be fed into the tank circuit centre tap. The base is ceramic for better resistance to heat and moisture. The VT61 was employed as the modulator valve in the transmitter of the 'Spitfire' fighter plane of WWII. Thus this valve was used for audio as well as RF.
The DET19 printed in typical M-OV style of the late 1930s.
The twin triodes with anode connections brought out to twin top caps.
The ceramic UX7 base. An American base on a UK valve.
The pinch components. It is quite clear that the heaters are run in parallel.
The top caps and heat radiating fins on the grid supports.
The classic envelope is 45 mm in diameter and, excluding the UX7 base pins, is 112 mm tall.
References: Datasheet. Type DET19 was first introduced in 1938.