The 41MDG is a dual grid mixer from Cossor. The mixer is an essential component in the superhet receiver. The signal is applied to one grid and a local oscillator voltage applied to the outer grid. The two frequencies multiply in the non-linear transfer characteristic of the valve and both sum and differences will be present in the anode circuit. The wanted frequency will be where the anode circuit is tuned and then further amplification at the Intermediate Frequency can take place before the signal is demodulated in the detector.
In addition to the B5 base there is an extra terminal on the side of the base.
It is indirectly heated and within the envelope can be seen the single hairpin heater within the flattened cathode tube. The grids are not close to the cathode and are wound from bright wire. The anode is a bright box with the sides replaced with a wire gauze.
The oval coated cathode can be seen clearly. Both grids pass flat across the cathode and the grid wires are held on notched and peened rods.
See also41MDG for the same valve with external metalising.
The balloon envelope is 48 mm in diameter and, excluding the B5 base pins is 104 mm tall.
References: 3002 & 1043. Type 41MDG was first introduced in 1932.