What is Vacuum tube: Definition and 28 Discussions

A vacuum tube, electron tube, valve (British usage) or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as a thermionic tube or thermionic valve uses the phenomenon of thermionic emission of electrons from a hot cathode and is used for a number of fundamental electronic functions such as signal amplification and current rectification. Non-thermionic types, such as a vacuum phototube however, achieve electron emission through the photoelectric effect, and are used for such purposes as the detection of light intensities. In both types, the electrons are accelerated from the cathode to the anode by the electric field in the tube.
The simplest vacuum tube, the diode, invented in 1904 by John Ambrose Fleming, contains only a heated electron-emitting cathode and an anode. Electrons can only flow in one direction through the device—from the cathode to the anode. Adding one or more control grids within the tube allows the current between the cathode and anode to be controlled by the voltage on the grids.These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.In the 1940s, the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, more efficient, reliable, durable, safer, and more economical than thermionic tubes. Beginning in the mid-1960s, thermionic tubes were being replaced by the transistor. However, the cathode-ray tube (CRT) remained the basis for television monitors and oscilloscopes until the early 21st century. Thermionic tubes are still used in some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers, and amplifiers that audio enthusiasts prefer for their "warmer" tube sound.
Not all electronic circuit valves/electron tubes are vacuum tubes. Gas-filled tubes are similar devices, but containing a gas, typically at low pressure, which exploit phenomena related to electric discharge in gases, usually without a heater.

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  1. S

    Electrical Need advice on building a linear particle accelerator

    I am a freshman in highschool and I plan on building a linear particle accelerator (DTL) I need help finding out how to find the drift tube length. I use the equation V=√(2eV/m) (where V is equal to the velocity. E is the elementary charge of the electron 1.602 x 10^-19. V is the applied...
  2. D

    B Has anyone ever done a double slit experiment in an electronic valve (vacuum tube)?

    i.e a vacuum tube. using the gate in a triode to adjust the amplification of the electrons. i guess you would have to have a photographic plate attached to the anode but this shouldnt effect the operation of the valve. just a thought... not sure where you would put the detector, maybe it would...
  3. Limebat

    I Does combusted gas travel faster in a vacuum tube?

    Hey all, So if a gas is combusted, would it travel faster through a vacuum tube or a regular ole' tube? I would assume the vacuum tube, as there are less particulates collisions in the way of the fast-moving gas molecules. Yet this also implies pressure on the outside of the thin barrier _ 2...
  4. Abimbola1987

    Measurement of vacuum diode electron flow

    Dear Sirs, After my theoretical post on vacuum diode electron flow, I decided to try and measure it physically. I didn't have a vacuum tube, so I improvised with some tungsten wire, aluminum sheets and some screws and the result was usable. Obviously the tungsten wire fails after some time due...
  5. Abimbola1987

    Understanding Electron Flow in Vacuum Diodes

    Dear Sirs I have been going through the "radiotron designers handbook", but I can't seem to find the answer to the doubt I have about the electron flow of the source Vp. Kindly consider the below two circuits, the difference is the polarity of Vf. Question: In both circuits, the electrons...
  6. HotFurnace

    Electric Potential Distribution in a Vacuum Diode

    Homework Statement This problem is belonging to a book, which is material for Vietnamese students who will take part in IPhO (International Physics Olympiad). Since this problem is written in Vietnamese, I will try my best to translate it to English: A vacuum diode consists of two parallel...
  7. K

    I Exploring the Optimal Dimensions and Materials for High Vacuum Transparent Tubes

    Hello For the purpose of the experiment, I wonder what the maximum dimensions can have a transparent tube, I thought over a diameter of 30cm and a length of 1-1,5m and from what material should such a pipe be made. I would like to get a high vacuum (about 0,2-2Pa)
  8. Planobilly

    Building a vacuum tube amp from scratch

    This is my first try at building everything myself. Programming the G Code to cut the chassis on my old Linux computer took a bit of thinking...lol Here is a short video. A few photos so far. I will post the schematic when I finish it. Cheers, Billy
  9. Planobilly

    How is it possible to run a 12AX7 vacuum tube at 415VDC?

    Hi, Here is the schematic link: http://www.classictubeamps.com/schematics/Mesa/Mesa%20Boogie%20Solo%2050%20Rectoverb%20schematic.pdf The 12AX7 inverter tube has a measured plate voltage of 416 VDC just like the schematic indicates. V1a rail voltage is 394VDC with a 200K plate resistor and a...
  10. Planobilly

    Questions about vacuum tube data sheets

    Hi, Here is a typical data sheet for a commonly used 6l6GC tube. http://www.drtube.com/datasheets/6l6gc-jj2003.pdf Under typical characteristics (in this data sheet) a value of Ra and Ra-a are given. I assume Ra-a means Za-a and it could also be written as Zout. Is this a correct assumption...
  11. Salvador

    Do Vacuum Tube Amplifiers Emit X-Rays at Lower Voltages and Frequencies?

    I recently got an older tube amplifier , since ti was dirty from being left for a long time in an old shed i took the covers off and cleaned it , now I am listening it also with the covers off , everything works etc. Now I wonder do tubes at lower voltages and lower frequencies such as in the...
  12. Planobilly

    Need Some Guidance For Testing Process On Vacuum Tube Amp

    Hi Guys, I am having issues trying to repair this amp. http://www.tangible-technology.com/schematics/fender/HR-Deville/Hot%20Rod%20DeVille.pdf A little history is in order I guess. I have not been working on guitar amps for too long, several months now. I have repaired perhaps fifty or so...
  13. J

    Vacuum tubes and electronic oscillators

    I've been reading up about vacuum tubes and (more specifically) the Audion, and how they were used for instruments/amplifiers. This isn't anything I'm learning about on my degree, just things I'm reading up on myself so forgive me if I'm a little slow to grasp some parts. I understand how the...
  14. EinsteinKreuz

    Vacuum Tube & Thyratron plate capacitance

    What factors determine the anode plate-to-grid capacitance? I know that the capacitance of a regular capacitor is determined by the surface area of the plates and is inversely proportional to the distance between them. Does this hold for vacuum tube grids and anode plates? The reason I'm asking...
  15. BeautifulLight

    How is the grid biased on a triode vacuum tube amplifier?

    Here is my single triode vacuum tube amplifier circuit I understand there needs to be a bias on the grid otherwise the signal will be rectified -not amplified. Is biasing the grid as simple as running a resistor in-between the grid and the cathode on the power supply like this (in red)...
  16. kq6up

    Cherenkov Radiation in a Vacuum Tube

    Someone on another forum shared with me that a 6L6 vacuum tube exhibits a blue dot when in operation that is supposed to be Cherenkov radiation. I say nay, as I have worked out the relativistic velocity using $$KE={ m }_{ 0 }{ c }^{ 2 }\left[ \frac { 1 }{ \sqrt { 1-\frac { { v }^{ 2 } }{ { c...
  17. kq6up

    Easier Way to Build Spice Models from Old Data Sheets

    I would like to find an easier way to build spice models from old data sheets. Normally one would have to tediously build spread sheet tables from curve traces of these old tubes. However, I was wondering if there is some sort of program that allows one to trace lines over the images, set...
  18. R

    Protecting an LM324 Op-Amp in a Vacuum Tube Deflection Amplifier

    Hello. Here joined is the schematic of a small deflection amplifier. Outputs H0 & H1 are connected to electrodes placed in a vacuum volume. These outputs are protected by varistors. High voltage to collectors is 200 V DC. Sometimes, not very often, the head Op-Amp (LM324) is burnt. The only...
  19. Y

    Is there vacuum tube models for LTspice?

    I know the default library of LTspice don't have vacuum tube model. Does anyone know where I can get one. If not, any other free spice program have vacuum tube models? The only one I find so far is: http://www.duncanamps.com/technical/ltspice.html I tried to follow the instruction and...
  20. I

    How does a vacuum tube get hot?

    Old CRT tv's use vacuum tubes and they get hot, but how does the glass get hot when the inside is under a vacuum and therefore shouldn't transfer any heat?
  21. S

    Supplying Power To A Mullard Vacuum Tube

    How would a curious young gentleman like myself go about supplying power to a Mullard vacuum tube? I have several different types of Mullard tubes, but no idea as to how I can generate the electron beam. P.S. If side-effects of solution include death, injury or Hannah Montana please do not post.
  22. M

    What Would Happen If a Vacuum Tube Connected Earth and Space?

    If you have a tube with no air in it, making the the tube a vacuum. And stuck one end in space and the other end in the Earth's ocean. Then Opened both ends. Would it suck all the water out into space? If not what would happen?
  23. D

    Crush pressure on an underwater vacuum tube

    So... let's say I wanted to drop a pipe on the ocean floor with a 6" inner diameter... which has a pretty strong vacuum in it... what general size/material do you suppose that would require... assume it is miles long. I guess you could keep the vacuum pipe inside of another pipe that does not...
  24. D

    Valve (vacuum tube) help please

    Hey I was just wanting to know, for something like a guitar amplifyer what is the inputted signal connected to on the valve (cathode, anode, filament or grid) and also what the outputed signal is connected to. thanx
  25. T

    Understanding Vacuum Tube Characteristics

    Hi all! OK, hopefully this will be a very quick question. Basically, I want to know how to model a vacuum tube (both triode and pentode) in terms of creating a dynamic system model. For example, if were to look at the voltage in an inductor as a function of time, I would employ the relation...
  26. N

    Vacuum Tube Amps vs. Solid State?

    It seems that amps using vacuum tubes are becoming more and more popular with musicians these days. They're a bit expensive, at least the models I've seen, and the claim is that these vacuum tube amps produce a better sound or a richer sound. I was wondering if there was a physics-based...
  27. S

    Learning Vacuum Tube Amplifiers for Senior Design Project

    Hey all; None of my EE classes cover vac tubes since they're largely obsolete. The thing is, for my senior design project (I have a year or so, no rush.) I'd like to build an audio amplifier. From experience I know the advantages of vac tubes and am willing to put up with the drawbacks...
  28. Tweek

    Where Can I Find a Vacuum Tube for Household Object Experiments?

    in which I could fit about a 3" diameter object in. I have searched and searched all over the net and I can't find any. I would like to purchase a vacuum tube so that I could do several experiments on what happens to household objects in a vaccum. I would like to see how ice changes in it among...