The VT61 transmitting double triode covers the VHF frequency range. The triode can be driven hard and this valve can accept a grid current of 15 mA. The number of equivalent types attests to its utility. This exhibit also carries the old stores code of 10E/11442.
The VT indicates a pre CV Register valve Type specified by the RAF. The VT61 was employed as the modulator valve in the transmitter of the 'Spitfire' fighter plane of WWII. The base cap is ceramic and impervious to moisture, a clear sign of a valve designed for aircraft use.
The twin triode sections. The anode of each section is connected to a top cap.
A closer view.
The classic envelope is 44 mm in diameter and, excluding the UX7 base pins, is 112 mm tall.
References: Datasheet. Type VT61 was first introduced in 1938.