The PM2DX was introduced in 1928 and is described by Mullard as being for detector and general purpose applications within battery broadcast receivers.The filament is for accumulator use and the anode is designed for dry battery operation with a maximum anode voltage of 150 Volts.The PM2DX was also popular as a driver valve for quiescent push-pull output stages such as the PM2B.The early production featured a balloon envelope whereas this exhibit is probably from 1932-33 and has a shouldered envelope. Internally the filament coating has progressed from the messy Azide process of the early PM valves.
The bright anode sits above the pinch with long supports that hold a top mica tight into the top of the envelope.
The filament tension springs hold the filament tight against the top mica to maintain a constant geometry within the grid.The classic envelope is 46 mm in diameter and excluding the B4 base pins, is 101 mm tall.Reference: Data-sheet. Type PM2DX was first introduced in 1928. See also 1928 adverts. |
