The 41MHL is an indirectly heated triode and was suitable for detector or audio amplifier in a radio receiver. Internally the valve has both a control grid and a screen grid. The latter is internally connected to the anode by a length of coiled wire.
Here the oval cathode and the two grids can be clearly seen. The control grid has been shaped to pass close to the cathode with the supports further away. The shaping seems to consist of pressing the wires together around a former to give the final shape. The second grid also has a fairly close pitch.
The wire helix connecting the anode to the second grid is in plain view. We have not discovered why this triode was made with the extra grid.
Another view.
The balloon envelope is 54 mm in diameter, and excluding the B5 base pins is 111 mm tall.
References: Data-sheet, 1043, 3002 & 1040. Type 41MHL was first introduced in 1930. See also1930 adverts.
