A Cathode Ray Tube is an earlier display technology that was used before LCDs and LEDs. It works in a similar way to an indirectly heated valve except it is much larger and the anode voltage exceeds 20,000 volts.

The job of the cathode (and associated components) is to create a tight beam of electrons that can be moved left-right and up-down. Those electrons hit the screen at the other end and create a bright dot. The beam can be moved in two ways, normal TVs use two magnetic fields and oscilloscopes use plates for deflection.




The most common way for the beam to move is called 'raster scanning'. This is where the beam moves left-to-right and top-to-bottom (see video) and this was used by CCTV and TVs.

The other method is 'vector' which was used by a few videos games.

By the 1990s and 2000s CTRs were slowly replaced by flat-screen technology like LCDs and LEDs.