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. This exhibit has a heat shrink plastic tube around the bottom of the glass and the ceramic base cap either to repair damaged cement or to strengthen the join against vibration.
Face view of the triode pair.
Side view. Note the horizontal busbars joining the heaters in parallel.
The bottom mica showing the tape connections to the supports moulded into the pinch and also the heater that passes through the cathode tube four times.
The classic envelope is 45 mm in diameter and, excluding the UX7 base pins, is 108 mm tall.
References: Data-sheet. Type VT61 was first introduced in 1938. See also1938 adverts.
