Although the PL82 would normally be found in frame output stage of a television receiver, a pair used as an audio amplifier in push pull class AB1 would deliver 9 Watts at 4 % distortion.
The peak to peak grid signal voltage would be 26 Volts and the shared anode load would be 4,000 Ohms.
Looking into the anode the three grids can be seen, indicating that this is a true pentode.
The top mica components including the radiating fins on the control grid supports.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 69 mm tall.
References: Data-sheet & 1040. Type PL82 was first introduced in 1951. See also1951 adverts.