The MH4 is an indirectly heated amplifier triode. The MH4 was also produced in Catkin form in 1933/4. The glass envelope version has a totally different electrode construction but gave the same results. The Catkins were excellent valves but were more expensive to make and were phased out after a few years.
The Marconi balloon envelope MH4 was also made with external metallising.
This exhibit has a clear envelope that allows a proper look at the construction including the mesh anode. The cathode tube has been partly flattened. The grid wires have been wound between two supports but shaped so that for most of the width the wires are pressed almost together. The centre section, passing round the cathode, has the wires opened out into an oval shape.
Side view.
The balloon envelope is 50 mm in diameter and, excluding the B5 base pins, is 111 mm tall.
References: Data-sheet, 1005, 1043, 3002 & 1040. Type MH4 was first introduced in 1929. See also1929 adverts.
