The thermionic valvesalso known as vacuum tubes or thermionic tubes, are electronic devices that use the emission of electrons from a heated filament to control the flow of current in a circuit.
These devices played a crucial role in the development of modern electronics, marking a revolution in the transmission and amplification of electrical signals; although they have been largely replaced by transistors since the mid-20th centurythermionic valves still maintain a particular fascination for electronics enthusiasts and find applications in specific fields.
The origins of thermionic valves
The history of vacuum tubes begins with the invention of the vacuum diode by John Ambrose Fleming in 1904. Fleming, a British electrical engineer, developed the diode to rectify radio signals, a critical step in receiving radio waves; subsequently, in 1907, the American inventor Lee De Forest introduced a third electrode, creating the triodewhich allowed the amplification of signals.
These developments paved the way for the use of vacuum tubes in a wide range of applications, from radio to telephony, contributing significantly to the evolution of communication technologies.
The applications of thermionic valves
Vacuum tubes have been widely used to amplify, rectify, and modulate electrical signals; in the first decades of the 20th century, they were fundamental to the development of radio and telephone communication systems.
Their ability to amplify weak signals made them indispensable for long-distance transmissions and for receiving radio signals; furthermore, valves were used in early electronic computers, such as the ENIAC, where they were used to make logic and memory circuits.
The first computer that ran on vacuum tubes
The first general-purpose electronic computer to use vacuum tubes was the ENIAC (Electronic Numerical Integrator and Computer); built between 1943 and 1945 at the University of Pennsylvania, the ENIAC computer was a mammoth device composed of approximately 18,000 vacuum tubes.
Designed to solve complex computing problems, primarily for military use during World War II, the ENIAC could perform operations at a speed unprecedented for its time; its construction and operation required constant maintenance due to frequent valve failure, but its success demonstrated the potential of electronic computers and paved the way for the future evolution of information technology.
What if computers today still ran on vacuum tubes?
If modern computers still used vacuum tubes, size, power consumption, and maintenance would be huge problems; a historical example is the ENIAC just mentioned, which occupied approximately 167 square meters and weighed 30 tons to perform operations that today a simple microchip can manage.
A modern processor, such as the average Intel Core i7 microchip, it contains billions of transistors in a space of just a few square centimeters; if you were to build a similar processor using vacuum tubes, it would be as large as a building and would require a dedicated power plant to power it and maintenance would be ongoing, as valves tend to fail frequently and require regular replacements, an impractical task for today’s complex, high-density systems.
Size and reliability limitations would make the evolution of portable devices and ubiquitous access to computing impossible; this makes us understand how its use today is impractical except in very particular cases which you will see shortly.
Radio and TV with vacuum tubes
Tube radios and televisions dominated the consumer electronics market until the 1950s and 1960s. The valves allowed audio and video signals to be amplified, making it possible to transmit and receive radio and television programs with a quality acceptable for the time.
Valve devices were known for their robustness and durability, although they required a warm-up period before being operational and they were relatively bulky and energy inefficient compared to modern technologies.
Their slow decline
The introduction of the transistor in the 1950s marked the beginning of the decline of vacuum tubes. Transistors, being smaller, cheaper and more energy efficient, they began to replace valves in many applications.
By the 1970s, most consumer electronic devices had made the transition to transistors, and vacuum tubes were gradually relegated to specific niches, such as high-quality audio amplification and some scientific and industrial equipment.
Are these valves still used in our era?
Despite their decline, vacuum tubes have not completely disappeared. They are still used in some specialist applications where their unique characteristics are appreciated; for example, many hi-fi enthusiasts prefer tube amplifiers for the warm, rich sound they produce.
Valves are used in some high-power radio transmitters and in scientific equipment that requires special signal handling capabilities that transistors cannot provide.
Concrete examples of their use in today’s era
Today, vacuum tubes still find application in several specific fields: a prominent example is that of electric guitar amplifiers.
Brands like Fender, McIntosh, and Marshall continue to produce tube amplifiers that are highly prized by musicians for their distinctive warm, dynamic sound.
Even in the field of high-fidelity audio, tube amplifiers are sought after by audiophiles who desire superior sound quality; Moreover, some high-power radio transmissions and scientific equipmentsuch as radar systems and nuclear fusion equipment, still use valves due to their ability to operate at high power and in extreme conditions.
Conclusion
Vacuum tubes represent a milestone in the evolution of electronics. Although they have largely been replaced by transistors and other more modern technologies, their historical impact is undeniable.
They enabled the development of radio and television communications and the first computers, laying the foundations for contemporary electronics; even today, in some specialized sectors, thermionic valves continue to demonstrate their value, confirming that, despite technological advances, there are still spaces where old technology finds its place.
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