The PL33 is a high sensitivity audio output pentode designed for universal equipment with 300 mA heater chains. Mullard specify this valve for up to nine watts anode dissipation. In addition to single ended audio applications the PL33 was designed with television frame output service in mind.
The first set of parameters is for single ended service and the second for a pair of valves operated in class A push pull. The grid voltage in the second set of figures is the peak to peak input voltage.
The anode side view.
The valve is a true pentode with three wire grids but it also has two vertical rods in the plane of the grids that connects to the cathode and suppressor grid. The anode cavity is oval.
The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 111 mm tall.