The Heart and Soul of Your Television

At the center of the standard projection-style television set is the all-important Cathode Ray Tube (CRT). You may have heard of a CRT before, but what exactly does it do? The answer to that is surprisingly simple and amazingly complex at the same time.

In science, the term “cathode” means a negative terminal. The opposite of a cathode is an “anode”, which means negative terminal.

In a CRT, the Cathode is a heated filament that creates electrons. The Ray is the stream of electrons that emanate from the cathode filament, and the Tube is the large glass vacuum (otherwise known as your picture screen) that houses the entire thing. It’s that simple.

Now it’s time for the complicated part.

The cathode, or negative-charged heated filament, creates negative charged electrons in a stream (the Ray part of the CRT, remember?). These electrons are compacted by a focusing anode terminal and an accelerating anode terminal, which causes the electron stream to be compacted into a tight beam travelling at a high rate of speed.

This electron beam is then directed at the inside of the flat screen (your viewing screen) at the opposite end of the tube. The flat area is coated in a thin layer of phosphor, a substance that lights up when it is struck by the electron stream.

The inside of the picture tube is also given a thin coating of conductive material, ensuring that all those electrons have somewhere to go after they hit the phosphors.

Now, if this was all there was to your CRT, all you would see when you turned the television on would be a tiny little circle of light, much like that tiny light in the center of old television sets when you turn them on or off. The electron beam needs to cross every pixel of phosphor on the screen to show an effective picture, and it does this with the help of steering coils.

A steering coil is a series of copper wires wrapped around the CRT to make an electromagnet. These electromagnets can create two separate electromagnetic fields within the CRT, one vertical and the other horizontal.

The electrode beam can be manipulated by changing the strength of these electromagnetic fields because it carries a negative charge. Using an X and Y axis style grid, the beam can be moved to point at any part of the picture screen.