Search Result for "vacuum_tube":
Wordnet 3.0

NOUN (1)

1. electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope;
[syn: tube, vacuum tube, thermionic vacuum tube, thermionic tube, electron tube, thermionic valve]


The Collaborative International Dictionary of English v.0.48:

Vacuum \Vac"u*um\ (v[a^]k"[-u]*[u^]m), n.; pl. E. Vacuums (v[a^]k"[-u]*[u^]mz), L. Vacua (v[a^]k"[-u]*[.a]). [L., fr. vacuus empty. See Vacuous.] 1. (Physics) A space entirely devoid of matter (called also, by way of distinction, absolute vacuum); hence, in a more general sense, a space, as the interior of a closed vessel, which has been exhausted to a high or the highest degree by an air pump or other artificial means; as, water boils at a reduced temperature in a vacuum. [1913 Webster] [1913 Webster] 2. The condition of rarefaction, or reduction of pressure below that of the atmosphere, in a vessel, as the condenser of a steam engine, which is nearly exhausted of air or steam, etc.; as, a vacuum of 26 inches of mercury, or 13 pounds per square inch. [1913 Webster] Vacuum brake, a kind of continuous brake operated by exhausting the air from some appliance under each car, and so causing the pressure of the atmosphere to apply the brakes. Vacuum pan (Technol.), a kind of large closed metallic retort used in sugar making for boiling down sirup. It is so connected with an exhausting apparatus that a partial vacuum is formed within. This allows the evaporation and concentration to take place at a lower atmospheric pressure and hence also at a lower temperature, which largely obviates the danger of burning the sugar, and shortens the process. Vacuum pump. Same as Pulsometer, 1. Vacuum tube (Phys.), (a) a glass tube provided with platinum electrodes and exhausted, for the passage of the electrical discharge; a Geissler tube. (a) any tube used in electronic devices, containing a vacuum and used to control the flow of electrons in a circuit, as a vacuum diode, triode, tetrode, or pentode. Vacuum valve, a safety valve opening inward to admit air to a vessel in which the pressure is less than that of the atmosphere, in order to prevent collapse. Torricellian vacuum. See under Torricellian. [1913 Webster]
WordNet (r) 3.0 (2006):

vacuum tube n 1: electronic device consisting of a system of electrodes arranged in an evacuated glass or metal envelope [syn: tube, vacuum tube, thermionic vacuum tube, thermionic tube, electron tube, thermionic valve]
The Free On-line Dictionary of Computing (18 March 2015):

electron tube firebottle vacuum tube (Or tube, vacuum tube, UK: valve, electron valve, thermionic valve, firebottle, glassfet) An electronic component consisting of a space exhausted of gas to such an extent that electrons may move about freely, and two or more electrodes with external connections. Nearly all tubes are of the thermionic type where one electrode, called the cathode, is heated, and electrons are emitted from its surface with a small energy (typically a Volt or less). A second electrode, called the anode (plate) will attract the electrons when it is positive with respect to the cathode, allowing current in one direction but not the other. In types which are used for amplification of signals, additional electrodes, called grids, beam-forming electrodes, focussing electrodes and so on according to their purpose, are introduced between cathode and plate and modify the flow of electrons by electrostatic attraction or (usually) repulsion. A voltage change on a grid can control a substantially greater change in that between cathode and anode. Unlike semiconductors, except perhaps for FETs, the movement of electrons is simply a function of electrostatic field within the active region of the tube, and as a consequence of the very low mass of the electron, the currents can be changed quickly. Moreover, there is no limit to the current density in the space, and the electrodes which do dissapate power are usually metal and can be cooled with forced air, water, or other refrigerants. Today these features cause tubes to be the active device of choice when the signals to be amplified are a power levels of more than about 500 watts. The first electronic digital computers used hundreds of vacuum tubes as their active components which, given the reliability of these devices, meant the computers needed frequent repairs to keep them operating. The chief causes of unreliability are the heater used to heat the cathode and the connector into which the tube was plugged. Vacuum tube manufacturers in the US are nearly a thing of the past, with the exception of the special purpose types used in broadcast and image sensing and displays. Eimac, GE, RCA, and the like would probably refer to specific types such as "Beam Power Tetrode" and the like, and rarely use the generic terms. The cathode ray tube is a special purpose type based on these principles which is used for the visual display in television and computers. X-ray tubes are diodes (two element tubes) used at high voltage; a tungsten anode emits the energetic photons when the energetic electrons hit it. Magnetrons use magnetic fields to constrain the electrons; they provide very simple, high power, ultra-high frequency signals for radar, microwave ovens, and the like. Klystrons amplify signals at high power and microwave frequencies. (1996-02-05)