This is one of the three battery catkin valves released by M-OV in 1934. These were dubbed 'Batkins' This valve has no identification. However, the box it came in was labeled MH4 and referenced The M-OV Saga book. That book does not confirm the type. Thrower gives the three battery catkins as VS24/K a vari-μ tetrode, HL2/K general purpose triode and PT2/k output pentode. Of these three only the PT2/K was fitted with a B5 base. Thus we have an identification.
The battery catkins external copper anode was not cylindrical like the mains versions. In the battery version the anode was diamond shaped in cross section. The filament was a V shape with side supports and the grid passed either side of the filament giving the flattened shape. There is no visible to a third grid from the pinch.
The battery catkins were introduced the year that M-OV phased out their external anode receiving valves. The problems of poor copper to glass seals in mass produced valves, some 50% reject rate, gave rise to the decision to stop this line of development. Imagine a catkin version of the KT66 or PX25.
We have the glass version of the PT2 in the museum and that data-sheet is attached.
The anode side view. The wire connects to anode to pin one of the base. The line in the Bakelite base indicates the orientation for pin one.
The connections seen across the width of the electrodes.
The filament in the centre, control grid connection below and screen grid above.
The diamond shaped copper anode.
The B5 base with the letters M-OV around the central pin.
The catkin envelope is 14[k[mm x 6 mm and, excluding the B5 base pins, is 97 mm tall.
References: 1005 & 1043. Type PT2/K was first introduced in 1934.