The Ever Ready S11D is the Mullard DW4/350 (DW4-350) with Ever Ready branding and is a full wave directly heated rectifier.
The 1936 DW4/350 specification is very close to the Mullard DW3 released in 1931. The difference in this later valve is a lower internal resistance allowing the output voltage for a 350-0-350 Volt input to be 380 Volts rather than the original 320 Volts.
An enhanced image showing the yellow lettering including the Ever Ready logo.
The twin rectifier sections.
The top mica showing the filament tension springs and the oxide coated filament ribbons.
The base of one anode showing the filament ribbon welded to the supports.
The classic envelope is 49 mm in diameter and, excluding the B4 base pins, is 114 mm tall.
References: Data-sheet & 1043. Type S11D was first introduced in 1936. See also1936 adverts.
