Tube Definition and 20 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.

View More On
  1. sumatoken

    Study of harmonic motion of a liquid in a V shaped tube

    A V-shaped tube with a cross-section A contains a perfect liquid with mass density and length L plus and the angles between the horizontal plane and the tube arms as shown in the attached figure. We displace the liquid from its equilibrium position with a distance and without any initial...
  2. J

    Filling a long tube by submerging it in fluid

    Hi everyone, I'm working on a first-year college assingment and need some help with it. I need to figure out how deep does a tube, initially filled with air, need to be submerged into water in order get fully filled, meaning in order for the air to be fully displaced by water. The tube is 1/2...
  3. L

    Help with formulas for calculating pressure

    Hi! This is my first post on here. I need to purchase an air cylinder, most likely hydraulic. The cylinder will have a forming die attached on the end and will be used to crimp two small stainless steel tubes together. The crimp will occur at an offset of .004 inches from each end of the tubes...
  4. P

    The electric field in an expanding, statically-charged tube

    Imagine that I have a straight, statically-charged, cylinder-shaped tube with arbitrary (ideally infinite) extent. The charge is distributed evenly over the tube such that the field inside the tube is zero. For convenience, let's line up the tube centered along the x-axis such that the...
  5. resurgance2001

    B Resonance of air between two loudspeakers

    A student I am working with showed me a problem they have been working on. In the first part of the question there are two loudspeaker facing each other. The student has been told that they can treat this situation as an closed tube. The frequency of the note is such that its wavelength is...
  6. W

    Tube and Shell exercise

    Homework Statement Would really appreciate if you could lend me a hand with this tube and shell exercise.[/B] m=0.24kg/s ##D=2.5*10-2m## ρ=850 kg/m^3 cp=2000 J/kg*K μ=2*10-4 kg/m*s λ=0.3W/m*k Homework Equations Dittus-Boelter:Nu=0.023*Re0.8*Prn where n=0.4 heating and n=0.3 for cooling, so in...
  7. A

    Automotive New In tube end forming practices -- Can I downsize and then upsize a pipe end?

    In tube end forming practices, is it possible to first reduce the diameter of the pipe (tube 0.9mm thick) and then expand it, at the same end, by about 1mm in total, with a transistion radius of 8mm ? Please see attached image. Though it might be exaggerated, but the image should suffice. I want...
  8. Tardis Traveller

    Maximum angle of the refracted light beam

    Homework Statement A light ray falls from the air (##n_a=1##) into the center of the upper surface of a long cilindrical glass tube with an index of refraction ##n_t=3/2##. The tube is submerged into water all the way to the upper edge and the waters index of refraction is ##n_w=4/3##. What is...
  9. faradayscat

    U-shaped tube fluid dynamics

    Homework Statement [/B] Suppose we have a u-shaped tube filled with water, with oil added at one end which disturbs the equilibrium. Now say one end is blocked off and the other is exposed to air flow which reduces the pressure above the water and causes the water to climb back to equilibrium...
  10. D

    Askew Pitot tube, airplane velocity measurement

    Homework Statement A horizontal Pitot tube (with one end open for airflow and another closed) is accidentally installed into an airplane askew, so that the tube is not horizontal. Instead the closed tube end is higher (in the y-direction of a xy-plane) than the inlet end. How does this affect...
  11. L

    Fluid oscillations in V-tube

    Homework Statement Basically, the goal of the "project" is to find the equation for oscillation of a "fractionless" fluid in a v-shaped tube, regarding the angle. I know how to solve the same problem regarding a u-shaped tube, but in this case, I can't figure out where to place the angle in the...
  12. kostoglotov

    Why is the open end of a tube a node for a standing wave?

    I understand, from my textbook, that certain frequencies of sound (depending on the length of the tube) will reflect off the interface between the air in the tube and the air outside, that this interface is a discontinuity. But in all other cases where discontinuities caused (partial)...
  13. Silverlight

    How to Find Force on Rubber Tube from Piston System?

    Hello, first of all, this isn't a homework/school related question. Long story short, my father works for a chemical plant and a few of their valve/piston/transfer system things have been breaking, which he assumes is because of too much force. With everyone in a dispute and doing their own...
  14. D

    Plate applying force to a tube - nonlinear analysis ansys

    I am trying to apply a force to the tube structure via the plate. I am struggling to get this to solve. Current set up is as follows: Frictionless contact between the two compenents displacement constraing the plate in the x direction force applied to the plate Could anyone offer some...
  15. A

    Standing waves in tube closed tube

    Homework Statement A tone with frequency 2,00 * 10^3 Hz is held above a tube filled with water. The water level is increased and decreased. When the water level is 5.7cm below the opening of the tube, the first sound maxima is heard. When the water level is 39.3cm below the opening of the...
  16. T

    Pressure wave in pipe

    1. Problem statement In a straight pipe there is at t = 0 an over-pressure for |x| ≤ a of the form p0(x) = A(1– |x| ), where A is small. The velocity is zero at t = 0. Determine the pressure in the pipe for x > 0 and t > 0. Determine also the pressure at the closed end located at x = L (L > a)...
  17. M

    Vortex Tube for cabinet cooling

    Hi, I'm a mechatronics student and I am currently working on a project on the effectiveness of a vortex tube to cool a cabinet. The cabinet has a thermostat inside and if the temperature exceeds a threshold, an air compressor is turned on, causing the vortex tube to cool the cabinet. The cabinet...
  18. B

    Volume flow through a one side closed capillary

    Hi everyone, I'm doing a simulation and need some help. A capillary which is closed on both ends with the length l (x=0 to x=l), with a radius R and the volume pi*R^2*l is dropped on a parachut at the time t=0 from a hight h above ground. At t=0 the pressure inside the capillary is p_i0 (this...
  19. D

    Flow through Interconnected Tubes

    Hello all, this is my first post here, so please excuse me if there are any mistakes or important information is left omitted. Now, my problem is quite intricate and specific so I will be thankful for any information I can get. Using Excel, I am looking to model the volume flow of air through...
  20. Fuichris

    Pulley / Fraying - "Mechanical Flower" Project

    Hi all, "MECHANICAL FLOWER PROJECT" I'm working on a personal hobby art project (non-academic, non-commercial, non-governmental) where I'm mechanizing petals of a plastic flower. Basically, making petals curl open and close. *Please see picture and video. GOAL: To pull continously without...