The 20P1 is a purpose designed self oscillating television line output valve. It is designed to withstand a positive anode surge voltage of 6 kV and a negative grid surge of -1.5 kV. The screen grid can dissipate 5 W.
This valve would be seen in television receivers of the 1950s.
The anode edge that reveals the beam plate and screen grid. The control grid is difficult to see.
The pinch and lower supports. The rectangular opening in the beam plate is clear to see.
The working face of the anode with side flange for greater radiating area.
The top mica with side sheets to grip the glass. The control grid radiator is substantial.
The classic envelope is 54 mm in diameter and, excluding the IO base pins, is 122 mm tall.
References: Data-sheet & 1040. Type 20P1 was first introduced in 1951.