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.
This exhibit is made by Telefunken and the brand logo is partly visible. The Type designation has only the final 1 visible. The pin connections match the PL81 and the heater matches the specification. However, the construction differs from the normal PL81 style.
The anode side view with beam plates within. Note the ceramic insulators at the base.
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.