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 base. 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.
Each of the control grid's supporting rods is fitted with a blackened metal fin to assist with the cooling of the grid. This can be seen above the top mica.
The end of the anode with the bright beam plate within. The anode flanges connecting to the supports are placed where the maximum heat is produced.
The STC logo and the commercial Type designation of 5B/254M.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 86 mm tall.
