Triode facts for kids

A triode is a special kind of glass tube with wires inside. People in Britain sometimes call it a "valve." Unlike a diode, which has only two wires (called electrodes), a triode has a third wire. This third wire is called the grid. It sits between the other two wires: the cathode (which sends out electricity) and the anode (which collects electricity).

What Does "Triode" Mean?

The word "triode" comes from two parts:

• "Tri" means three.
• "Ode" means way or path.

So, "triode" means "three paths" or "three ways," referring to its three main parts.

How a Triode Works

When the cathode inside the triode gets hot, it sends out tiny electricity particles called electrons. The anode then collects these electrons. This creates a flow of electricity, also known as an electric current.

The special part is the grid. The grid acts like a "gate" or "controller." It checks how many electrons can pass through from the cathode to the anode. By changing how much electricity the grid has, it can control the flow of electrons. This ability to control the electric flow makes the triode useful as an amplifier. An amplifier is a device that makes electric signals stronger.

The grid can also quickly change the amount of electrons it lets through. Because of this, triodes can be used to create electric waves (as an oscillator) or to detect waves.

The History of Triodes

The idea for the "grid" came from Philipp Lenard in 1902. He wanted to create a device that could collect electrons.

Later, in 1904, John Ambrose Fleming created the diode, which was called the "Fleming valve." It only had two parts.

Then, in 1908, Lee de Forest and Robert von Lieben improved on the diode. They added the third wire (the grid) and created the triode. Lee De Forest had made his own two-part device called the Audion in 1906. The triode was important because it could make electric signals stronger. People gave it the name "triode" to show it was different from other vacuum tubes like the diode, tetrode, or pentode.

People wanted to talk to others far away. Triodes helped make this possible with radio receivers (which pick up waves) and radio transmitters (which send out waves). At first, they only sent Morse code. But as triodes got better, people could talk to each other using radio.

Triode transmitters were so good that they replaced older crystal transmitters. This helped make new listening devices like earphones.

Around 1920, triodes helped start radio broadcasting. This meant sending radio waves to many people at once. Triodes also made long-distance telephone calls much better.

The "Bell Telephone" group used triodes to make telephones that could pick up waves from about 800 miles away. People were very excited when the first long triode wave transmitters were used for the transcontinental telephone line across the Atlantic Ocean on January 25, 1915.

Other inventors used triodes in their creations, leading to new technologies like early television, public address systems, electric phonographs, and talking motion pictures.

Over time, people started adding more wires inside these tubes. Walter Schottky created the tetrode (with four wires) in 1916. Then, Gilles Holst and Bernandus Dominicus Hubertus Tellegen created the pentode (with five wires) in 1926.

Triodes were used in many devices like radios, televisions, and audio systems for a long time. However, in 1947, a new, smaller, and more powerful device called the transistor was invented. The transistor eventually replaced the triode in most uses.

What Triodes Are Used For Today

Even though transistors are common, triodes are still used today.

• They are used in some special audio machines and music equipment because of the unique sound they produce.
• They are also used in screens that glow, like vacuum fluorescent displays (VFDs).
• Some radios and heaters still use triodes to heat things or to pick up waves.

The triode is like an ancestor to the transistor. While transistors have mostly replaced triodes in many devices since the 1960s, triodes are still important in vacuum tube amplifiers and other specific uses.

Images for kids

• 

  De Forest Audion tube from 1908, the first triode. The flat plate is visible at top, with the zigzag wire grid under it. The filament was originally under the grid but has burned out.

• 

  Examples of low power triodes from 1918 (left) to miniature tubes of the 1960s (right)

• 

  Soviet lighthouse tube 6С5Д (6S5D)

• 

  ECC83 triode operating characteristic.

See also

In Spanish: Triodo para niños