The VT61A transmitting double triode was designed for use up to 150 MHz. It was made by Rogers of Canada and carries the Air Ministry markings. The VT prefix is an Air Force designation. The glass also carries the old stores code of 10E/142. Clearly this was made before 1941 when the CV register was introduced.
The operating parameters, but not the heater values, given are from the 4074A and this was a UX7 based valve as this is the closest match to the VT61A we could find. The 4074B is a B5 based valve of pinch construction in a classic glass envelope. The anodes are brought out to separate top caps.
Triodes were favoured for transmitter work over tetrodes because of lower capacitances and an ability to be driven harder. This valve was designed to pass a grid current of 17 mA.
The twin triode sections with both anodes connected to top caps. The fluted top cap appears to be a Rogers feature.
The AM and Crown on the base cap and above one anode is seen full face. The control grids have U shaped heatsinks fitted.
The classic envelope is 45 mm in diameter and, excluding the B5 base pins, is 107 mm tall.