Old TVs, early supercomputers, and modern fancy sound equipment all use vacuum tubes. But why? What does a vacuum tube do?
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At the time they were made they were revolutionary. They were essentially the best way to make a diode at the time, which is an essential component in all electronics. Even today’s microprocessors are nothing more than many very tiny diodes.
[this video](https://youtu.be/FU_YFpfDqqA?si=9HmEVCQZpQqZNnPd) explains everything perfectly
It acts as a kind of switch that can be turned on or off with a small electrical signal. (Same function as a transitor actually just takes up gobs of space in comparison)
The electrical signal can be much much weaker than the circuit you are actually turning on and off.
So let’s say I have a microphone. It can use a tiny bit of a special crystal to generate an electrical signal from sound waves. If I were to hook this up to a speaker you could barely hear it and it’s a very very small voltage(if it made it move at all)
What I can do is take that tiny signal and hook it up to the “exciter” post (the part that receives the on/off signal) of a vacuum tube and then have 120V (household plug voltage in Canada/USA) on the switched part. The speaker now can see the 120V being turned on and off at the same frequency that the microphone signal is being emmitted.
Lots of other uses for them but amplifying signals like this is one of the main ones
Vacuum tubes were replaced by modern transistors.
Transistors act like valves where an input voltage A can control how much voltage flows through input B, to output C. This is really useful for, say, a radio where you can have a *really tiny* voltage on A that opens the “valve” and lets a much larger voltage through B, which makes it an amplifier.
It also lets you use one voltage A as a switch to turn on or off voltage B, which lets you do all sorts of things with logic gates.
So how do vacuum tubes do this? Put two plates of metal and put a positive charge on one and negative on the other, and put them in a vacuum. Electrons will “jump” off of the negative plate and onto the positive plate, creating a voltage that flows across the plates. Then, put another plate between them with lots of holes, or a grid of wires. If you put a positive charge on the grid, it’ll help the electrons jump across and increase the voltage. If you put a negative charge on it, it’ll block the electrons and reduce or completely stop the voltage.
So, just like the transistors that came afterwards, the vacuum tube acts as a “switch” where the input on A (the grid) controls the voltage passing through the plates (B and C).
A vacuum tube can do similar things as what semiconductors do today.
The simple function is a diode, it only allows current trough it in one direction. A more complex but also more useful function is as an amplifier. A small input current can control a large output current. This is what transistors do and what is used in amplifiers and computer applications.
The first vacuum tube was made in 1904 and it was a good. The first semiconductor are made in 1940 but it is not until 1960 that transistors start to replace vacuum tubes for applications like television and radio receivers. It was at that point that got cheaper.
Vacuum tubes have been and are to some degree still used in some applications where semiconductors have problems iwh the power levels. The high-power amplifier in TV or radio broadcasts, radar systems etc.
But for many other applications like computers semiconductors are superior. The last vacuum tube computer was made in early 1960.
Audio is another usage. The harmonic they create especially if you overdrive an amplifier. You get even-order harmonics with tubes but even-order harmonics with transistors. You can listen to the difference in https://www.youtube.com/watch?v=RUpvAdF3M2M
This is for simple amplifiers. You can build a digital system that creates distortion like tubes do if you just do not over the amplifier. There is a lot of stuff audiophiles do and purchase that makes no difference if you do a blind test, very expensive cables that claim to have special properties are an example. They even have claims for digital cables which it can have no effect at all, they are just a scam.
Tube amplifiers are in large part because most of them will not be driven so you get distortion, so a way companies try to make more money. It is not a total scam because there is a difference but in practice, it do not have a noticeable effect for most. The main advantage is you can boast about your amplifier to your friends.
Honestly, just watch this video: https://youtu.be/FU_YFpfDqqA
It goes into the history of lightbulbs to transistors and the mechanics of how/why the transition happened.
A vacuum tube is a switch with no mechanical parts. It allows you to turn one current on or off with another current.
A vacuum tube has 3 terminals, a place where current goes in, goes out, and a controller.
Current goes into the one side, and a beam of electrons is created from there. The controller can steer that beam of electrons by cresting a magnetic field. If it steers the beam right, it can hit the other side and allow current to come out the other side. If you change the controller current, the beam no longer makes contact and current stops.
This process creates a lot of waste heat and light, and vacuum tubes need to warm up before use to function properly. Due to that heating and cooling, they are prone to breaking.
They fell out of use when the transistor was invented. The transistor does the same job, but without needing to warm up, a fraction of the energy, and with 1000x the reliability.
Fun fact: CRTs (cathod ray televisions, the old big ones) use a similar method to work. The TV signal comes in and turns an electron beam on and off while another current steers that beam into the screen. The electron beam then hits phosphors (chemicals that light up when hit with high energy) that glow with the corresponding color of that pixel, resulting in an image scanned one line at a time on the screen.
Fun fact: the term “debugging” comes from the fact that vacuum tubes would sometimes burn moths onto them, and impede their function, so you would occasionally have to “debug” the system by removing the dead moths.
Perhaps part of your question is “why use vacuum tubes when there is and has been a more reliable alternative”? If so, I can tell you as a card carrying audiophile that there is a belief held by many serious audio aficionados (myself included) that vacuum tubes portray the music that plays through them as more relaxed, melodic or inviting than music played back through a modern transistor based amplifier. Perhaps some of it is simply the beautiful lighted glow a nice 300B amplifier tube portrays, but we also know that the type of distortion (minimal) that a vacuum tube creates sounds more natural or pleasing to the human ear. Could a transistor produce the same or more power far more efficiently and reliably? Absolutely. But for the same reason some people enjoy taking 10 minutes in the morning to make pour over coffee when they could just press the button on the Keurig, some people enjoy the ceremony of using vacuum tubes.
They were the original way of amplifying signals and rectifying AC to DC. They existed since the early 20th century. Transistors weren’t invented until 1948.
The two main uses of vacuum tubes in audio are for home stereo systems and in guitar amps.
In both situations they are amplifiers. They take a tiny electric current and turn it into a very big one that can physically move a speaker cone.
You can easily make high quality amplifiers with semiconductors (transistors) that are very powerful and much cheaper. So why do people still like tubes? It’s because of what happens when you send too much signal into the input.
In both cases you get distortion. However the distortion created by a tube amp is more pleasant sounding.
That makes sense when you’re playing guitar and you *want* a distorted sound. You deliberately over drive the input to your amp because you like the sound that results. Also back when electric guitars were invented, tube amps were the only options. So the original sound of the electric guitar, by definition, was that of a tube amp.
But when you’re talking about listening to already recorded music on your home stereo…you shouldn’t be over driving the input. So the kind of distortion produced by the amp shouldn’t really matter.
The mainstream application of vacuum tubes these days is the magnetron in your microwave oven, which is a special oscillator that can put out kilowatts of power at 2.4 GHz. CRT’s are also a kind of vacuum tube, but we have pretty much replaced those with LCD or LED technology.
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