Vacuum tube

They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers.

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.

Power is dissipated by the filaments, and by electrons from the cathode impacting and heating the anode (plate); this occurs even in an idle amplifier due to the quiescent current necessary to ensure linearity and low distortion.

It was years later that John Ambrose Fleming applied the rectifying property of the Edison effect to detection of radio signals, as an improvement over the magnetic detector.

[16] Being essentially the first electronic amplifier,[17] such tubes were instrumental in long-distance telephony (such as the first coast-to-coast telephone line in the US) and public address systems, and introduced a far superior and versatile technology for use in radio transmitters and receivers.

As a result of experiments conducted on Edison effect bulbs,[15] Fleming developed a vacuum tube that he termed the oscillation valve because it passed current in only one direction.

In 1906, Robert von Lieben filed for a patent for a cathode-ray tube which used an external magnetic deflection coil and was intended for use as an amplifier in telephony equipment.

[28] Irving Langmuir at the General Electric research laboratory (Schenectady, New York) had improved Wolfgang Gaede's high-vacuum diffusion pump and used it to settle the question of thermionic emission and conduction in a vacuum.

The plate current of the triode was not accurately proportional to the grid voltage, i.e. the operating characteristic was non-linear, causing early tube audio amplifiers to exhibit harmonic distortion at low volumes.

To combat the stability problems of the triode as a radio frequency amplifier due to grid-to-plate capacitance, the physicist Walter H. Schottky invented the tetrode or screen grid tube in 1919.

Many designs use such a screen grid as an additional anode to provide feedback for the oscillator function, whose current adds to that of the incoming radio frequency signal.

The RCA Type 55 is a double diode triode used as a detector, automatic gain control rectifier and audio preamplifier in early AC powered radios.

Their distinctive orange, red, or purple glow during operation indicates the presence of gas; electrons flowing in a vacuum do not produce light within that region.

X-ray tubes used for continuous-duty operation in fluoroscopy and CT imaging equipment may use a focused cathode and a rotating anode to dissipate the large amounts of heat thereby generated.

This ionization process ensures reliable and consistent operation by providing a steady current when a high voltage is applied, thereby improving the tube's performance and stability.

The heater's failure mode is typically a stress-related fracture of the tungsten wire or at a weld point and generally occurs after accruing many thermal (power on-off) cycles.

In particular, tubes made for computing use are designed for long life when used biased to cut-off most of the time, but significant hum, microphony and noise—very undesirable in audio applications—are not important.

The vapor is deposited on the inside of the glass envelope, leaving a silver-colored metallic patch that continues to absorb small amounts of gas that may leak into the tube during its working life.

An arc can be caused by applying voltage to the anode (plate) before the cathode has come up to operating temperature, or by drawing excess current through a rectifier, which damages the emission coating.

Overheating of internal parts, such as control grids or mica spacer insulators, can result in trapped gas escaping into the tube; this can reduce performance.

Tubes on standby for long periods, with heater voltage applied, may develop high cathode interface resistance and display poor emission characteristics.

Although there are still many televisions and computer monitors using cathode-ray tubes, they are rapidly being replaced by flat panel displays whose quality has greatly improved even as their prices drop.

This is also true of digital oscilloscopes (based on internal computers and analog-to-digital converters), although traditional analog scopes (dependent upon CRTs) continue to be produced, are economical, and preferred by many technicians.

[87] At one time many radios used "magic eye tubes", a specialized sort of CRT used in place of a meter movement to indicate signal strength or input level in a tape recorder.

Historically, the image orthicon TV camera tube widely used in television studios prior to the development of modern CCD arrays also used multistage electron multiplication.

One variant called a "channel electron multiplier" does not use individual dynodes but consists of a curved tube, such as a helix, coated on the inside with material with good secondary emission.

In general, vacuum tubes are much less susceptible than corresponding solid-state components to transient overvoltages, such as mains voltage surges or lightning, the electromagnetic pulse effect of nuclear explosions,[97] or geomagnetic storms produced by giant solar flares.

[citation needed] A UK company, Blackburn MicroTech Solutions, developed radically different versions of standard tubes for the audiophile market.

[103] In the early years of the 21st century there has been renewed interest in vacuum tubes, this time with the electron emitter formed on a flat silicon substrate, as in integrated circuit technology.

Such integrated microtubes may find application in microwave devices including mobile phones, for Bluetooth and Wi-Fi transmission, and in radar and satellite communication.