The 6P28 is a television line output beam tetrode valve. The line output stage is essentially a pulse operation where the valve is driven hard on and the current grows linearly in the line deflection coils.
The anode dissipation is 15 Watts and the screen 4.5 Watts. It is suggested that the cathode resistor be 100 Ohms. The valve is designed to work with positive anode surges of up to 5,000 Volts. The electrode geometry reflects this high voltage design.
The side elevation of the anode. The bright structure within is the beam forming plates.
The side of the anode in close-up. The screen grid passes flat across the broad face of the anode. The control grid is just visible as a series of points along the support rods.
The classic envelope is 54 mm in diameter, and excluding the IO base pins is 126 mm tall.
Reference: 1040. Type 6P28 was first introduced in 1948.