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.Mullard also specify the PL81 for use as a series pass element in voltage regulators.This valve looks to be little used as the ceramic insulator has not discoloured with use.
There is some discolouration on the envelope but far less than one normally sees.
As expected of a power valve, the control grid is wound on copper supports and there are heat radiating fins on the tops of the supports.The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 74 mm tall.References: Data-sheet & 1040. Type PL81 was first introduced in 1951. See also 1951 adverts. |
