The CV428 miniature beam tetrode has the same ratings as the classic 807. The difference in size between the 807 and this valve shows the extent to which valve technology matured during WWII and the effect of the introduction of the pressed glass foot. The B8B base was the earliest to be developed (by Sylvania in the US) with eight equi-spaced pins and an external metal collar to hide the envelope seal and secure a locating spigot.
The Commercial Type designation of 5B/254M is also on the glass together with the maker ITT. This example was made in England, and for ITT that was by STC.
The angled screen grid fin can be seen above the top mica. Inside the anode is the bright metal beam plate.
Looking directly at the grids shows the heat sink fin on the top of the screen grid.
The wide glass tube envelope is 29 mm in diameter and, excluding the B8B base pins, is 89 mm tall.