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.
A glass envelope of all glass construction is enclosed by the thin aluminium can.
The remains of the Marconi brand label.
The base pins with the distinctive M-OV bottom cover and spigot.
The wide glass tube envelope is 34 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.
