The 20P4 is purpose designed as a television line output valve.
In September 1953 Mazda described the 20P4 as having a redesigned g2 with consequent reduction in screen dissipation and increase in power handling on positive pulses. The sensitivity of the valve has also been increased. This exhibit looks like an early version.
The valve can withstand a positive anode surge of 6 kV. The screen grid can dissipate 5 Watts.
Through the holes in the end wall of the anode the beam forming plate can be seen as a bright sheet.
Looking closely between the two halves of the beam plate the inner grids can be seen. The cathode is a rectangular box and the grids are shaped so as to pass flat across the active face of the cathode.
The anode face view. The flat cathode tube and inner grid can be seen as can the beam plates that confine the electron flow to the width of the control grid.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 91 mm tall.
References: Data-sheet & 1040. Type 20P4 was first introduced in 1953.