The PL81 was designed for universal mains sets without a mains transformer and with the heaters on a series chain. The parameters given are for a pair in push pull audio service.
As a line output valve in television service, the peak anode surge voltage is 7,000 Volts. The anode dissipation is 8 Watts.
The PL81 is also suitable for use as a series pass element in voltage regulators. Typically it would be the 6.3 Volt version the EL81 that would be chosen.
The characteristic ceramic insulator. The copper supports for the control grid are topped with radiating fins.
There are fins on each control grid support.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 75 mm tall.
References: Data-sheet & 1040. Type PL81 was first introduced in 1951. See also1951 adverts.
