Half-Wave Rectifier
The 81 Vacuum tube is a glass type used in power supplies
of radio receivers. They require a four-contact socket
and should be mounted preferably in a vertical position.
Horizontal mounting is permissible if pins 1 and 4 are
in a horizontal plane.
Electrical Data
Filament Voltage .............................. 7.5 V
Filament Current .............................. 1.25 A