The original MS4 dates to 1929 and the first production was with the then standard screw top cap. This exhibit has lost the screw top cap but the cement on the glass clearly shows it was of the large type.
The MS4B glass version was issued before the catkin version MS4B that was issued in 1933/4. Later production was again in a glass envelope but with the classic shouldered shape rather than the earlier balloon with the cylindrical glass skirt up to the lower screen. This feature was to allow for the valve to be mounted through the chassis for maximum screening.
MS4B is a tetrode from the early mains valve era with its 4 Volt heater and it offered 'maximum amplification', whereas the earlier MS4 was a general purpose screened grid valve. The screened tetrodes and pentodes were employed for RF and IF amplification.
The Osram paper label and the black of the gettering inside the glass behind the label.
The construction has a fully screened set of inner electrodes. The screening box has an outer solid band with the faces facing the anodes made of wire mesh.
The small anodes are placed either side of the screen grid and are connected together and held at the top by the top cap. Near the base the anode is held in a glass bead with the wires the other side of the bead being connected to the lower screen.
The balloon envelope is 43 mm in diameter and, excluding the B5 base pins, is 111 mm tall.
References: Data-sheet & 1040. Type MS4B was first introduced in 1931. See also1931 adverts.
