The 161D from Mullard is that company's implementation of the DET1SW from M-OV. The DET1 was introduced in 1924 and operated to 2 MHz. The later DET1SW was designed for Short Wave working at a frequency of up to 30 MHz. DET1 had an anode dissipation of 35 Watts, DET1SW and 161D both had anode dissipations of 40 Watts. All ran with around 1,000 Volts on the anode. The DET1 filament was 6.0 Volts at 1.9 Amps and the 161D probably has the same rating.
The bright box anode needed a short connection to the outside world for higher frequency working and that is why it connects to the top cap. Hot glass becomes lossy at RF and this is why the centre sections has been made wider to keep it cooler.
The box anode is shorter than the control grid that can be seen extending either side. The filament tensions springs are below the anode and placed just above the pinch. The thoriated tungsten filament passes through the anode/grid four times.
A clear view of the pinch and lower components. The envelope carries the serial number of 159 and this is also present on the pinch.
The evelope lettering including a patent reference.
The Mullard Logo and trade mark. Above the anode the method of fixing the tops of the filament strands can be seen. The central spacer ensures a more even distribution of emission across the width of the valve.
Another view of the whole valve showing the hole in the metal top cap.
Under the gettering at the top of the valve can be seen a wide closed tube. To this tube is clamped the anode supports.
The balloon envelope is 76 mm in diameter, and excluding the L4 base pins is 195 mm tall.