The 30PL13 triode beam tetrode was designed specifically for service in a frame output stage of a television receiver. The requirements are low power and low frequency service. As with nearly all later television valves the heater is designed for 300 mA and operation as part of a chain across the mains supply.
This exhibit differs from 30PL13 in the fact that a screen is fitted between the triode and beam tetrode sections.
This close-up shows the screen and the triode section. Looking into the hole in the anode the control grid can be seen. Looking at the right hand side the filament can be seen to start forming a coil before it enters the cathode.