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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 although the main purpose of the PL81 was as a television line output valve or a series pass element in stabilised power supplies.

As a line output valve in television service, the peak anode surge voltage is 7,000 Volts. The anode dissipation is 8 Watts.

The anode is held in place by ceramic formers. The design is a beam tetrode and the beam plates are held in the mica supports.

The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 72 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type PL81 was first introduced in 1951. See also 1951 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.