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Electric lamp

Lecture



Electric lamp

Russian export radio lamp 6550C

An electric lamp , a radio lamp is an electrovacuum device (more precisely, a vacuum electronic device), working by controlling the intensity of the flow of electrons moving in a vacuum or rarefied gas between the electrodes.

Radio tubes were massively used in the twentieth century as active elements of electronic equipment (amplifiers, generators, detectors, switches, etc.). Currently, almost completely replaced by semiconductor devices. Sometimes they are also used in high-power high-frequency transmitters and audio equipment.

Electronic lamps intended for illumination (flash lamps, xenon lamps, mercury and sodium lamps) are not called radio tubes and usually belong to the class of lighting devices.

Electron-beam devices are based on the same principles as radio tubes, but, in addition to controlling the intensity of the electron flow, also control the distribution of electrons in space and, therefore, are separated into a separate group. Also separately emit microwave microwave devices using resonant phenomena in the electron beam (such as a magnetron).

Content

  • 1 principle of operation
    • 1.1 Vacuum tubes with heated cathodes
    • 1.2 Gas-filled electronic lamps
    • 1.3 Microelectronic devices with autoemission cathode
  • 2 History
  • 3 Construction
    • 3.1 Cathode
    • 3.2 Anode
    • 3.3 Grid
    • 3.4 cylinder
  • 4 Basic Types
  • 5 Current applications
    • 5.1 High-frequency and high-voltage powerful equipment
    • 5.2 Military industry
    • 5.3 Space technology
    • 5.4 Increased ambient temperature and radiation
    • 5.5 Audio equipment
  • 6 Classification by name
    • 6.1 Markings adopted in the USSR / Russia
    • 6.2 Markings in other countries
  • 7 See also
  • 8 Discharge lamps
  • 9 See also
  • 10 Notes
  • 11 References

Operating principle

Vacuum tubes with heated cathodes

  • As a result of thermionic emission, electrons leave the cathode surface.
  • Under the influence of the potential difference between the anode (+) and the cathode (-), the electrons reach the anode and form the anode current in the external circuit.
  • With the help of additional electrodes (grids), the electron flow is controlled by applying electric potential to these electrodes.

In vacuum tubes, the presence of gas degrades the characteristics of the lamp.

Gas-filled electronic lamps

The main for this class of devices is the flow of ions and electrons in the gas that fills the lamp. The flow can be created, as in vacuum devices, by thermionic emission, or it can be created by the formation of an electrical discharge in a gas due to the intensity of the electric field.

Microelectronic devices with autoemission cathode

The process of miniaturization of electronic vacuum tubes led to the rejection of heated cathodes and the transition to autoelectronic emission from cold cathodes of a special form from specially selected materials. [1] This makes it possible to bring the size of devices to micron sizes and use standard manufacturing processes of the semiconductor industry in their manufacture. [2] Currently, such constructions are being actively investigated.

Story

Electric lamp

The Triode ("Audion") of Lee de Foresta, 1906

Electric lamp

The first Soviet radio lamp. Exposition of the Museum of Novgorod Radio Laboratory

In 1883, Edison tried to increase the service life of a carbon filament lighting lamp in a vacuum glass flask. To this end, in one of the experiments, he introduced a metal plate with a conductor bred out into the vacuum space of the lamp. During the experiments, he noticed that the vacuum conducts current, and only in the direction from the electrode to the heated thread and only when the thread is heated. It was unexpected for that time - it was believed that the vacuum can not conduct current, since there are no charge carriers in it. The inventor did not understand then the significance of this discovery, but, just in case, he patented it.

Thanks to these experiments, Edison became the author of a fundamental scientific discovery, which is the basis for the operation of all electron tubes and all electronics before creating semiconductor devices. Subsequently, this phenomenon is called thermionic emission.

In 1905, this “Edison effect” became the basis of the British patent by John Fleming on “a device for converting alternating current into direct current” - the first electronic lamp that opened the age of electronics. [ source not specified 1943 days ]

In 1906, American engineer Lee de Forest introduced a third electrode into the lamp - a control grid (and thus created a triode). Such a lamp could already work as a current amplifier, and in 1913 an autogenerator was created on its basis.
In 1921, A. A. Chernyshev [3] [4] proposed the design of a cylindrical heated cathode (indirectly heated cathode).

Electric lamp

Miniature rod pentodes produced in the USSR

Vacuum electronic lamps became the element base of computers of the first generation. The main disadvantage of electronic lamps was that devices based on them were rather cumbersome. To supply the lamps, it was necessary to supply additional energy to heat the cathode (it is it that emits the electrons necessary for the current in the lamp), and the heat generated by them is removed. For example, in the first computers thousands of lamps were used that were placed in metal cabinets and took up a lot of space. Weighed such a machine tens of tons. For her work required power. To cool the car used powerful fans in connection with the release of lamps huge amounts of heat.

The peak of the heyday (“golden era”) of lamp circuitry fell on the years 1935-1950.

Design

Electric lamp

Elements of the electronic lamp (pentode):
Filament, cathode, three grids, anode. Above - fasteners and a ring with an air residue absorber.

Electron tubes have two or more electrodes: cathode , anode and grid .

Cathode

In order to ensure the emission of electrons from the cathode, it is additionally heated [3] .

According to the method of heating, the cathodes are divided into cathodes of direct and indirect heat.

The direct-heated cathode is a metallic filament made of metal with high electrical resistivity. Direct-heat lamps require less power, heat up faster, there is no problem of providing electrical insulation between the cathode and the filament (this problem is significant in high-voltage kenotrons). However, they usually have a shorter service life; when used in signal circuits, they need to be powered by direct current, and in a number of schemes they are not applicable due to the effect of potential difference in different parts of the cathode on the lamp operation.

The indirectly heated cathode is a cylinder, inside which a filament (heater) is placed. Such lamps are called indirect lamps.

To facilitate the emission of electrons, the cathodes of the lamps are usually activated — they are coated with a thin layer of a substance having a relatively small work function: thorium, barium, and their compounds [5] . The activating layer in the process of work is gradually destroyed and the lamp loses its emission. Purely metal cathodes (for example, in high-power lamps with a high cathode current density) are made of tungsten.

Anode

Electric lamp

Electron tube anode

Positive electrode It is sometimes performed in the form of a plate, but more often in the form of a box surrounding the cathode and the grid and having the shape of a cylinder or parallelepiped. In high-power lamps, the anode can have ribs or “wings” to remove heat. It is usually made from nickel or molybdenum, sometimes from tantalum and graphite.

Grid

Between the cathode and the anode are grids that serve to control the flow of electrons and eliminate side effects that occur when electrons move from the cathode to the anode.

The grid is a grid of thin wire, or more often made in the form of a wire helix, wound on several supporting racks (traverse). In rod lamps, the role of grids is performed by a system of several thin rods parallel to the cathode and anode, and the physics of their work is different than in the traditional design.

By appointment, the grids are divided into the following types:

  • Control grid - by changing the voltage on which you can adjust the anode current of the lamp, thereby forcing to amplify the signal;
  • Shielding grid - eliminates the parasitic connection between the control grid of the lamp and the anode. This grid is connected to the positive pole of the anode power source. If the output of the anode accidentally departs, then a large amount of current can flow through this grid, causing damage to the lamp. To prevent this phenomenon, a resistor of several kilo-ohm is included in series with a shielding grid;
  • Antidynamic grid - eliminates the dinatron effect that occurs when electrons are accelerated by the field of the shielding grid. The anti-inatron grid is connected to the cathode of the lamp, sometimes this connection is made inside the lamp balloon.

Depending on the purpose of the lamp, it can have up to seven grids. In some embodiments of switching on multigrid lamps, separate grids can act as an anode. For example, in a generator according to the Schembel scheme on a tetrode or pentode, the generator itself is a “virtual” triode formed by the cathode, the control grid and the screening grid as the anode [6] [7] .

Balloon

The brilliant sputtering (getter), which can be seen on the glass of most electron tubes, performs a dual function - the residual gas adsorbent, as well as a vacuum indicator (many types of getter turn white when air enters the lamp if it is damaged).

Metal electrodes (current leads) passing through the glass body of the lamp must be matched in terms of the coefficient of thermal expansion with this brand of glass and well moistened with molten glass. They are made of platinum (rarely), platinite, molybdenum, etc. [8]

Main types

Electric lamp

Compact ("finger") radio tubes

The main types of electronic vacuum tubes:

  • Diodes (easily made at high voltages, cm Kenotron)
  • Triodes
  • Tetrodes
  • Pentodes
  • Beam tetrodes and pentodes (as varieties of these types)
  • Hexodes
  • Heptodes
  • Octodes
  • Nonodes
  • Combined lamps (actually include 2 or more lamps in one cylinder)

Modern applications



Electric lamp

Ceramic-metal generating triode GS-9B with air cooling (USSR)

High-frequency and high-voltage powerful equipment

  • In high-power broadcasting transmitters (from 100 W to a few megawatts), high-power and super-powerful lamps with air or water cooling of the anode and high (more than 100 A) heating current are used in the output stages. Magnetrons, klystrons, so-called. The traveling-wave radiolamp provides a combination of high frequencies, power, and an acceptable cost (and often just the fundamental possibility of existence) of the element base.
  • Magnetron can be found not only in the radar, but also in any microwave oven.
  • If necessary, rectification or fast switching of several tens of kV, which cannot be done with mechanical keys, it is necessary to use radio tubes. So, the kenotron provides acceptable dynamics at voltages up to a million volts.

Military industry

Due to the principle of operation, electronic lamps are devices that are much more resistant to such damaging factors as the electromagnetic pulse. In a single device there may be several hundred lamps. In the USSR, rod lamps were used for use in onboard military equipment in the 1950s, which were distinguished by their small size and high mechanical strength.

Electric lamp

Miniature lamp type "acorn" (pentode 6ZH1ZH, USSR, 1955).

Space technology

The radiation degradation of semiconductor materials and the presence of the natural vacuum of the interplanetary medium makes the use of certain types of lamps a means of improving the reliability and durability of spacecraft. Application in AMSLuna-3 transistors was associated with great risk. [9]

Increased ambient temperature and radiation

Lamp equipment can be designed for a larger temperature and radiation range of conditions than semiconductor.

Audio equipment

Main article: Tube Sound

Electron tubes are still used in sound engineering, both amateur and professional. Designing tube sound engineering devices is one of the directions of the modern amateur radio movement.

Classification by name

Markings in other countries

In Europe in the 1930s, the leading manufacturers of radio tubes adopted the Common European system of alphanumeric marking:

- The first letter characterizes the filament voltage or its current:

A - voltage of 4 V;

B - filament current 180 mA;

C - filament current 200 mA;

D - filament voltage up to 1.4 V;

E is the filament voltage of 6.3 V;

F - voltage of 12.6 V;

G is the filament voltage of 5 V;

H - filament current 150 mA;

K - filament voltage 2 V;

P - filament current 300 mA;

U - filament current 100 mA;

V - heat current 50 mA;

X - heating current 600 mA.

- The second and subsequent letters in the designation determine the type of lamps:

A - diodes;

B - double diodes (with common cathode);

C - triodes (except weekends);

D - output triodes;

E - tetrodes (except weekends);

F - pentodes (except weekends);

L - output pentodes and tetrodes;

H - hexodes or heptodes (hexode type);

K - octodes or heptodes (octode type);

M - electronic and indicator lights settings;

P - amplifier lamps with secondary emission;

Y - half-wave kenotrons (simple);

Z - full-wave Kenotrons.

- A two-digit or three-digit number indicates the exterior design of the lamp and a serial number of this type, with the first digit usually characterizing the type of base or leg, for example:

1-9 - glass lamps with lamella base (“red series”)

1x - lamps with an eight-pin base ("11-series")

3x - lamps in a glass cylinder with an octal base;

5x - lamps with an octal base;

6x and 7x - glass subminiature lamps;

8x and from 180 to 189 - glass miniature with a nine-pin foot;

9x - glass miniature with a seven-pin leg.

Discharge lamps

Electric lamp

Tiratron

Discharge lamps typically use discharge in inert gases at low pressures. Examples of gas discharge tubes:

  • Gas discharge zener diodes
  • Gas arresters for protection against high voltage (for example, on air lines, receivers of powerful radars, etc.)
  • Thyratrons (three-electrode lamps - gas-discharge triodes, four-electrode - gas-discharge tetrodes)
  • Kraytrony
  • Geiger - Muller Counters
  • Xenon, neon lamps and other gas-discharge light sources.

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Radio tubes and ion devices

Terms: Radio tubes and ion devices