The 442BU is a full wave rectifier from Cossor. The data sheet shows a family of these rectifiers. It is probable that the 442 designation was awarded to the device when tested.
Not the best of conditions but the remains of the printed identification clearly show this to be a Cossor valve.
The oxide coated ribbon filaments are supported and tensioned by coil springs located above the top mica.
The classic envelope is 50 mm in diameter and, excluding the B4 base pins, is 111 mm tall.
References: Data-sheet & 1043. Type 442BU was first introduced in 1931. See also1931 adverts.
