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. The originally white lettering has darkened through many hours of operation.
The only difference between this exhibit and 20P4 is the brown base cap rather than a black base cap.
The working face of the anode. The two halves are joined at this point and the extra metal acts as additional heat sinking.
Close-up of the side of the anode revealing the inner two grids and the bright beam plates. At full size the image clearly shows the effect of the notch and peen system of forming a trough in the grid support and flattening the displaced metal back over the imbedded wire.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 91 mm tall.
References: Datasheet & 1040. Type 20P4 was first introduced in 1953.