SM243     Cathode Ray Oscillograph tube     circa 1965     Electricity

  In the cathode ray oscillograph a fine beam of electrons is deflected in two planes perpendicular to each other by means of voltages applied between X and Y plates respectively.   The beam is observed on a screen made of fluorescent material.

  The electron beam is emitted from a cathode heated in an evacuated enclosure by a filament.   This beam is controlled in intensity by passing through a plate with a central hole and kept at a negative potential with respect to the cathode.   The beam is accelerated and focused by means of three anodes that are at a high positive potential.   The middle anode, termed A2, is a cylinder and acts as a lens, focussing the beam to a fine point on the screen.   The pairs of deflection plates follow the anodes and enable the tube to display varying voltages on two perpendicular axes on the screen.   The assembly that generates the beam of electrons, which consists of a filament, cathode, grid and anodes, is called an electron gun.

  In some cases, notably in the television tube, deflection of the electron beam is magnetic, performed by two sets of coils with axes as right angles.