The famous beam power valve type KT-66 made in England by MO-Valve
In Electronics old times, inventors, engineers, scientists and same manufacturers if had not only involved in constants and long relative legal processes the breaking of rights of manufacture as of patents covering devices, components, as well as electronic circuits. Thus, in the Termionic field the rule could not be differentdid and, circa of 1939, in intention to prevent the breaking of patents that protected the pentode valve, made that some manufacturers after intense research of laboratory launched in the market the first electron beam power valve, known as directed beam tetrode. In the reality, this type of valve can in such a way have the structural configuration of one tetrodo as of one pentode and received this denomination for being constructed of form that the electrons circulate in intent beams of the catode through the screen until the plate. Thus, the main differences this valve, when compared with the tetrodes and conventional pentodes, they inhabit in the fact that in the spaces in the screen is lined up, possesss two plates producers of beams and, generally the space enters the shield screen and the plate is biggest. As the spaces between screen meet lined up, few electrons that collide against the shield grating and, therefore, the anodic current is greater that when compared with pentodes. In this type of valve the secondary emission is reduced due to space load enters the shield screen and the plate. The space load is a resultant phenomenon of the lockwire of electrons when they pass of the gratings of raised shield of potential for the plates where the same it is lesser. Thus, the formed space load in the front of the plate is enough to banish secondary electrons from the same one, emitted as resulted of the collision of primary electrons.
Several types of beam power valve type 6L6 made in the USA. From left to right bulbs types CC, G and metal
Internal structure of a beam power valve Beam-confining electrode