High transconductance wide-band cathode-ray gun

The ¿screen-grid amplifier gun¿ is a combination of a conventional tetrode-type gun with an amplifier constituted in large measure by the gun´s existing electrodes. In its simplest version the gun has, in fact, only one electrode more than conventional guns. The new gun has three grids participating in the beam mod ulation process: an auxiliary input grid and the two grids of the immersion lens. These latter grids are coupled together and operated 180° out of phase with respect to the input grid. Transconductance and resolution have been divorced from each other to a large extent in the screen grid amplifier gun. The low shunt capacitance makes the gun particularly suitable for wideband operation. Favourable possibilities are offered by this development for building guns with smaller ¿gamma¿ than hitherto possible. Analytical expressions correlating the gun´s beam current to various types of gun drive, namely, combined screen and control grid drive, control grid drive and cathode drive are derived for cathode-ray guns of conventional design. An analytical expression for the gun´s modulation constant is also given. Television guns possessing excellent resolution characteristics and transconductance in excess of 500 ¿mhos may be obtained rather simply. High transconductance guns and structures are shown.