What is a Cathode Ray Tube?

N. Madison

A cathode ray tube (CRT) is a type of analog display device. It is a special, electronic vacuum tube that uses a focused electron beam to display images. Though tubes of this type are used for many purposes, CRTs are most famous for their use in such things as televisions, oscilloscopes, computer and radar displays, and automated teller machines. They are also used in video game equipment.

Cathodes incorporate heated filaments.
Cathodes incorporate heated filaments.

A cathode or negatively charged terminal in a cathode ray tube is a heated filament, much like the filament seen in a light bulb. The filament is contained inside a vacuum within a glass tube. Inside the tube, a beam of electrons is allowed to flow from the filament into the vacuum. The flow of the electrons is natural, not forced.

CRT is an abbreviation for a cathode ray tube, often used in older model TVs.
CRT is an abbreviation for a cathode ray tube, often used in older model TVs.

When used inside a television set, a CRT’s electrons are concentrated into a tight beam by a positively charged terminal, called an anode. An accelerating anode is then used to speed up the movement of the electrons. These fast-moving electrons fly through the tube’s vacuum, hitting the phosphor-coated screen and making it glow.

A cathode ray tube television.
A cathode ray tube television.

A German physicist named Karl Ferdinand Braun is credited with inventing the cathode ray tube in 1897. His invention consisted of a tube with a fluorescent screen. This new technology was called a cathode ray oscilloscope. The screen of this tube would display a light when a beam of electrons touched it. Braun’s cathode ray oscilloscope is considered the predecessor of modern tubes used in television sets.

In 1929, Vladimir Kosma Zworykin created another type of CRT. Called the kinescope, it was designed for used with some of the earliest televisions. Two years later, Allen B. Du Mont introduced the first tube that was considered practical for use in a television set. It was also more durable than some of the previously introduced CRTs.

The cathode ray tube still plays a major part in television sets and many other electronic devices. However, there have been many new developments in display technology, such as plasma screens, liquid crystal display televisions (LCD TVs), and digital light processing (DLP) devices. Organic light-emitting diode (OLED) displays are also used to produce images. Still, the CRT maintains its popularity in television systems, as evidenced by the fact that the television is frequently referred to as “the tube.”

Cathode ray tubes play an important role in oscilloscopes.
Cathode ray tubes play an important role in oscilloscopes.

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Discussion Comments


@David09 - Here’s an interesting bit of trivia. The first computer ever invented was made entirely of cathode ray tubes. It was the ENIAC computer, built around the late 1940s I believe, and had stacks and stacks of cathode ray tubes to do its processing.

This was before the transistor came on the scene. Imagine a computer made up of thousands of tubes. It’s like wiring your house for Christmas. One tube goes out and you have to track it down and replace it, otherwise everything won’t work right.


@NathanG - I still have a Pentium II collecting dust in my basement and it’s got a cathode ray tube monitor that still works. I was told that the lifespan on these things was supposed to be 8 years but I’ve had it for 12 years and it’s still going strong.

I use it from time to time when I don’t need to do any heavy duty stuff. At all other times I use my newer computer with the flat panel.


I had a cathode ray tube TV for the longest time, even as the rest of the world was moving into flat panels. I just thought that I would stay with my trusty cathode ray tube television for as long as I could hold out before I had to switch to flat panel televisions.

One day that choice was thrust upon me. We had a major electrical storm and our house was zapped, and with it went the tube in my trusty cathode ray television that I’d held onto for more than ten years. That was my excuse to get a flat panel (the wife understood).

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