Cathode-Ray Tube. People who think vacuum tubes are obsolete clearly haven't looked in their television set. CRT's work by using an electron gun at the back, which uses a heater to liberate electrons from the cathode. A high voltage electric field exists between the cathode and the anode, which is located further into the tube. This accelerates the electrons to a high speed. During transit, deflection coils located on the neck of the CRT bend the resultant beam so that it can hit different parts of a phosphor coated screen. There are also focusing coils, correction magnets and other devices on the tube to insure uniform focus and illumination.

By moving the beam around, you can draw pictures. You can either draw vector graphics by using the beam itself to draw the picture, or you can generate a raster by scanning the entire screen several times a second and modulating the brightness to produce an image.

There are also color CRT's, which use three electron guns, a shadow mask, and red, green, and blue phosphors to produce full color images.