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. The original MS4 dates to 1929.
It 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 brand label.
The screen grid has woven wire mesh fixes to side and top plates to form a box. The control grid within is traditionally wound between two support rods.
The screen side supports look to be folded outwards with the mesh folded in and clamped to form both support and connection.
The etched Type designation appears within a circle. This etching style predates the elliptical shape of the outer lettering. The top of the screen is formed in the same way as the sides and at the top of the image can be seen the folds of box and mesh. The anode is made from two small plates - ribbed to prevent flexing - supported at the top by the mica disc tightly fitting the glass and at the bottom by wires that pass into glass bead insulators fixed to the lower screening tray.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 118 mm tall.
References: Data-sheet & 1040. Type MS4B was first introduced in 1931. See also1931 adverts.
