A TV tube, formally called a cathode ray tube (CRT), is the large glass vacuum tube that powered nearly every television set from the mid-20th century until flat screens took over in the 2000s. It works by firing a beam of electrons at a phosphor-coated screen, which glows wherever the beam strikes. That glow, repeated thousands of times per second across the entire screen, creates the image you see.
What’s Inside a CRT
A TV tube is essentially a funnel-shaped glass envelope with the air pumped out to create a vacuum. At the narrow end sits an electron gun, a small structure that heats a metal cathode until it releases a stream of electrons. These electrons are accelerated forward by extremely high voltages. The conductive coating inside the glass envelope operates at around 20,000 volts, while the electron gun assembly runs at roughly 2,000 volts. That voltage difference pulls the electrons toward the wide, flat end of the tube at tremendous speed.
The wide end is the screen itself, coated on the inside with phosphor, a material that emits visible light when struck by electrons. The brightness of any given spot depends on how intense the electron beam is at that moment. A stronger beam makes a brighter dot; a weaker beam makes a dimmer one. In a color TV tube, three separate electron guns fire at red, green, and blue phosphor dots, and the combination of those three colors at varying intensities produces every color you see on screen.
How the Image Gets Drawn
A CRT doesn’t display an entire image at once. Instead, the electron beam sweeps across the screen line by line, starting at the top left corner, moving horizontally to the right, then snapping back to draw the next line down. This happens so quickly that your eyes perceive it as a complete, stable picture. A standard television signal at 60 Hz draws a full frame every 16.7 milliseconds.
The beam is steered by a component called the deflection yoke, which wraps around the neck of the tube just behind the screen. The yoke contains two pairs of electromagnetic coils. One pair pushes the beam left and right (horizontal deflection), and the other pushes it up and down (vertical deflection). By rapidly changing the current flowing through these coils, the yoke can aim the electron beam at any point on the screen with extreme precision.
Color CRTs add another layer of complexity. A thin metal plate called a shadow mask sits just behind the phosphor screen, perforated with tiny holes. Each hole is aligned so that the red gun’s beam can only hit red phosphor dots, the green gun hits green dots, and the blue gun hits blue dots. Werner Flechsig patented this shadow mask design in 1938, and it became the foundation for virtually all color CRT televisions that followed.
The Rise and Peak of CRT Television
The basic concept of directing electron beams at a screen dates to the late 1800s, but practical television took decades to develop. The first demonstration of a fully electronic color TV display came in August 1944. Color broadcasts launched commercially in the United States in 1953, though adoption was painfully slow. Sets were expensive, and there simply wasn’t much color programming to watch.
It took nearly two decades for color to win out. The number of color TV sets sold in the U.S. didn’t surpass black-and-white sales until 1972, the same year that more than half of American households finally had a color set. From there, CRTs dominated living rooms worldwide for another three decades before LCD and plasma flat panels began replacing them in the early 2000s.
Why Some People Still Use CRTs
CRT televisions have a dedicated following among retro gaming enthusiasts, and the reason comes down to how the technology handles motion and timing. Because a CRT draws the image line by line as the signal arrives, there’s almost no delay between the console sending a frame and that frame appearing on screen. A CRT television displays about half a frame before the picture is visible, resulting in roughly 8.3 milliseconds of latency. An LCD monitor, by contrast, needs to receive the entire frame before displaying it, which means a minimum of 16.7 milliseconds at 60 Hz, and often more once the panel’s own processing time is factored in.
That difference of a few milliseconds matters in fast-paced games where split-second reactions determine the outcome. Older games were also designed with CRT display characteristics in mind. The slight softness of phosphor glow and the natural blending between scan lines were part of the intended look, and many pixel art styles that appear harsh on a sharp LCD screen look smoother and more polished on a tube TV.
High Voltage and Safety Risks
If you ever come across an old CRT, the most important thing to know is that the tube can hold a dangerous electrical charge long after being unplugged. The large glass envelope acts as a capacitor, storing energy at voltages that can reach several thousand volts. A CRT’s internal capacitor can discharge enough current to cause a serious shock. UC Berkeley documented a case where a worker received an electric shock from a capacitor holding 5,000 volts, with the current entering one hand and exiting the other, simply by coming within a quarter inch of the charged component.
This is why opening or disassembling a CRT television is not a casual project. The tube must be properly discharged before anyone works near the internal components. The glass envelope itself is also under vacuum, meaning it can implode if cracked, sending shards outward. Professional repair technicians were trained specifically for this work, and even experienced hobbyists treat CRT internals with considerable respect.