This exhibit is a Type 57 Rectifier that we have called 57.. to avoid confusion with other 57s.
It is a directly heated full wave rectifier with bright anodes that suggest a small maximum current.
The The twin sections have their top supports embedded in the central glass rod. The glass rod also holds the filament tensioning springs. The use of the glass insulator rather than a top mica suggest that this design dates to the 1920s.
The central glass insulator.
The dome carries the 'OK' name, the fact that is a rectifier and that manufacture was not in the UK but was imported to the UK. The pejorative term Foreign appears on the glass. The filament can be seen to have cracks in the oxide coating.
The filament tension spring and the oxide coated filament wire.
The balloon envelope is 50 mm in diameter and, excluding the base pins, is 103 mm tall.
