The W81 is a variable μ amplifier pentode. It is a high impedance device with a medium mutual conductance. Variable μ devices are primarily designed for IF and RF amplifiers in radio receivers. The anode current is quite high, this suggests that the device may have been designed for low noise input stages of HF communications receivers as noise performance improves when operated at higher power.
The all glass envelope glass is enclosed by the thin aluminium can.
The Marconi brand label.
The flat topped can with the wider lower portion that holds the plastic base cover and spigot. The spigot is hollow and protects the evacuation tube seal.
The base held by the folding over of the aluminium can. The short hard pins are equi-spaced around the pitch circle. The locating spigot thus has a key to ensure the correct orientation.
The wide glass tube envelope is 33 mm in diameter, and excluding the B8B base pins, is 60 mm tall.
Reference: 1040. Type W81 was first introduced in 1947. See also1947 adverts.
