Electron tube - this name perfectly emphasizes the main feature of a radio tube as an electronic device, the operation of which is based on the use of electron movement. What is the participation of electrons in the operation of a radio tube?
Metals contain many semi-free, i.e., electrons weakly bound to the atoms. These electrons are in constant motion, just as all particles of matter - atoms and molecules - are in constant motion.
The movements of electrons are chaotic; To illustrate such chaotic movement, a swarm of mosquitoes in the air is usually cited as an example. The speed of electron movement is considerable: in rough numbers it is approximately 100 km/sec - this is 100 times greater than the speed of a rifle bullet.
But if electrons fly in a metal in different directions, like midges in the air, and at such enormous speeds, then they probably fly outside the body.
This doesn't actually happen. The speeds that electrons have under normal conditions are not sufficient for their flight from the thickness of the metal into outer space. This requires much higher speeds.
Electronic emission
How can you increase the speed of electrons? Physics provides the answer to this question. If you heat a metal, the speed of electrons will increase and eventually can reach the limit when electrons begin to fly out into space.
The speed required for this is quite high. For example, for pure tungsten, from which radio tube filaments are made, it is equal to 1270 km/sec. Electrons reach this speed when tungsten is heated to 2,000° and above (here and below, degrees are indicated on an absolute scale).
The emission of electrons by a heated metal is called thermionic emission. Electron emission can be likened to the evaporation of liquids.
At low temperatures, evaporation does not occur at all or very little. As the temperature increases, evaporation increases. Violent evaporation begins when the boiling point is reached.
Evaporation of liquid and thermionic emission of metals are largely similar phenomena.
To obtain thermionic emission, the metal must be heated, and the method of heating does not matter. But in practice, it is most convenient to heat the metal with an electric current.
In vacuum tubes, the heated metal is given the appearance of thin filaments heated by electric current. These threads are called filaments, and the current that heats them is called incandescent current.
We mentioned that to produce emission, the metal must be heated to a very high temperature - about 2,000 and even higher. Not every metal can withstand this temperature; Most metals melt at such high temperatures.
Therefore, filaments can only be made from very refractory metals; They are usually made from tungsten.
Rice. 1. Lamp filament temperature.
At t = 2000°, tungsten begins to emit electrons.
The first samples of electronic tubes used purely tungsten filaments. At the temperature required to produce emission, the tungsten filaments glowed until they glowed white, which is where the name “lamp” came from, by the way.
However, such “illumination” is very expensive. To heat the lamp filament to white heat, a strong current is needed. Small receiving lamps with a pure tungsten filament consumed a filament current of half an ampere.
But soon a way was found to reduce the filament current. Research has shown that if tungsten is coated with certain other metals or their compounds, the emission of electrons is facilitated.
For takeoff, lower speeds are required, therefore less heating of the filament is required, which means such a filament will consume less filament current.
Improving lamp filaments
We will not give here the history of the gradual improvement of filaments, but will immediately point out that modern oxidized filaments operate at a temperature of about 700-900 ° C, i.e., a barely noticeable orange-red glow.
In this regard, it was possible to reduce the filament current by about 10 times. A modern ten-tube receiver consumes approximately the same filament current as a receiver that had only one old-style tube.
The process of coating filaments with emission-facilitating compounds is called activation, and the filaments themselves are called activated.
Activated filaments are good in all respects, except for one thing: they are afraid of overheating, that is, increased heating above normal.
If the activated thread is overheated, the layer of activating substance applied to it will evaporate; As a result, the filament will lose its ability to emit electrons at low temperatures.
Such a lamp is said to have “lost emission.” The filament of such a lamp is intact, the lamp “burns”, but does not work. This circumstance should be remembered and never allow the lamp filament voltage to exceed the normal value.
Of course, a lamp that has lost its emission could be made to work by raising its filament to a white glow. But the filaments of modern lamps are made very thin and, since at white heat the metal of the filament is atomized quite quickly, the filaments soon burn out.
Cathodes
The filament is an electron emitter in electronic devices. IN practical schemes When using these devices, these emitters are always connected to the negative pole (minus) of the main power source, which is why they are called cathodes. Therefore, the filament that serves to emit electrons can be called a cathode.
But it should be noted that a hot filament does not always serve as a direct emitter of electrons. Sometimes it is used only as a heat source, with the help of which another metal body is heated, which is already a source of electrons necessary for the operation of the lamp.
In other words, the functions of heating and emitting electrons are not always combined, i.e., the filament is not always the cathode.
So, for example, if the cathode is made in the form of a thin thread, it is convenient to feed such a thread DC from galvanic cells or from a battery, since its heating requires a small current; the cathode turns out to be economical.
But thin filaments are not suitable for AC power.
For normal operation of electronic devices, the cathode must emit the same number of electrons all the time. To do this, its temperature must be maintained strictly constant.
When the thread is powered by batteries or accumulators, this condition is met. But when the thread is powered with alternating current, it can no longer be observed.
The alternating lighting current changes its magnitude and direction 100 times per second (twice during each period). 100 times per second the current reaches its greatest value and decreases to zero the same number of times.
It is quite obvious that the temperature of the filament will fluctuate in accordance with changes in the current value, and at the same time the number of emitted electrons will also change.
True, due to thermal inertia, the filament will not have time to completely cool down in those moments when the current passes through zero, but nevertheless the fluctuations in its temperature and the magnitude of the electron emission turn out to be very noticeable.
This circumstance did not previously allow the use of such a convenient current source as a lighting network to power electronic devices that used the thermal emission of electrons.
Numerous attempts to make the filament suitable for heating with alternating current by increasing its thickness have had little success. A complete solution to this issue was provided only by the implementation of the proposal of our scientist A. A. Chernyshev on the construction of a heated cathode.
Heated cathodes are currently used throughout the world. Most electronic devices of all types are designed to be powered from a lighting network AC and has heated cathodes.
In heated cathodes, the filament itself is no longer a source emitting electrons. The direct electron emitter is isolated from the filament and is only heated by it.
This is where the name “heated” cathode comes from. The mass of the emitter is made large enough so that it does not have time to cool down while the heating current decreases. It goes without saying that such cathodes cannot produce emissions immediately after the filament current is turned on. They take approximately 15 to 30 seconds to warm up.
The designs of heated cathodes vary, but the principle of their design is generally the same. In old designs, the heater was made in the form of a ceramic tube with a diameter of about a millimeter with two through channels along its length.
A heating thread was passed into these channels. In more modern designs, a layer of heat-resistant insulation is applied directly to the heater filament.
To do this, the thread is coated with a compound that, after appropriate treatment, hardens, covering the heater with a heat-resistant shell that has fairly good insulating properties at high temperatures.
A nickel cylinder coated on the outside with a layer of oxide, which is actually an electron emitter, or cathode, is placed on the heater.
Such cathodes have three terminals - two from the ends of the heating filament and one from the emitter. The first two. are usually called the filament leads, and the third is called the cathode lead.
The emission of the heated cathode is completely uniform.
The cylindrical shape of the heated cathode is the most common, but not the only one. Some modern vacuum tubes use end-type cathodes in the shape of a cup, the bottom of which is coated with oxide on the outside.
Such cathodes are used, in particular, in cathode ray tubes, which we will meet later.
If the electron emitter is the filament itself, then such a cathode is sometimes called a directly heated cathode; if the filament only heats the emitter, then such a device is often called an indirectly heated or indirectly heated cathode.
Vacuum. Anyone who has seen a vacuum tube knows that it is enclosed in a glass or metal cylinder from which the air has been pumped out. The air inside the cylinder is extremely rarefied.
The air pressure on the surface of the earth, i.e. pressure of one atmosphere, corresponds to approximately 760 mm Hg. Art., and the air pressure inside the vacuum tube cylinder is only about 10^-7 mm Hg. Art. and even less, that is, about 10 billion times less than atmospheric pressure. This degree of rarefaction is called high vacuum (vacuum in Russian means emptiness).
Why is vacuum needed in a vacuum tube?
Firstly, it is needed to preserve the filament. If the filament, heated to almost a thousand degrees, was simply in the air, it would very soon burn out. Heated bodies are quickly oxidized by atmospheric oxygen.
Secondly, a vacuum is needed for the unimpeded movement of electrons escaping from the filament. The operation of a vacuum tube is based on the use of electrons emitted from a filament.
However, in order for electrons to be used properly, they must not encounter any obstacles on their way. Air is such an obstacle.
Rice. 2. The air pressure inside the radio tube cylinder is approximately 10 times less than atmospheric pressure.
Molecules and atoms of gases that make up the air surround the filament in countless quantities and prevent the flight of electrons. In order to reduce the possibility of electrons colliding with gas particles, the air inside the cylinder is rarefied.
A special role in creating a vacuum is played by the so-called “getters”, or absorbers. The fact is that with mass production of lamps, it would be too long and unprofitable to bring the vacuum in them to the required degree using pumps.
That's why they act differently. With the help of pumps, only a preliminary, so to speak rough, rarefaction of the air in the lamp is produced. The pressure is adjusted to one thousandth or even only one hundredth of a millimeter of mercury.
And for stable operation of the lamp, it is necessary that the pressure in it be less than one millionth of a millimeter of mercury. To obtain this high vacuum, a substance is sprayed into the lamp, which has the ability to greedily absorb gases. For example, the metals magnesium, barium and some compounds have this property.
To spray a getter in a glass-enclosed lamp, a coil fed by a high-frequency current is brought near it. The getter tablet mounted on a nickel plate inside the lamp heats up and evaporates.
Its vapors settle on the glass and form that silvery (with a magnesium getter) or dark metallic coating (with a barium getter) that we see in most glass vacuum tubes.
This metallic deposit greedily absorbs all remaining gases, and the pressure in the lamp drops to a millionth of a millimeter of mercury, which is already quite enough for stable and reliable operation of the lamp.
In such a rarefied gas environment, electrons propagate almost unhindered. When moving inside the lamp, no more than one electron in a million encounters a gas molecule along its path.
Russian export radio tube 6550C
Electronic lamp, radio tube- an electric vacuum device (more precisely, a vacuum electronic device) that works by controlling the intensity of the flow of electrons moving in a vacuum or rarefied gas between the electrodes.
Radio tubes were widely used in the twentieth century as active elements electronic equipment(amplifiers, generators, detectors, switches, etc.). Currently, they are almost completely replaced by semiconductor devices. Sometimes they are also used in powerful high-frequency transmitters and high-quality audio equipment.
Electronic lamps intended for lighting (flash lamps, xenon lamps, and sodium lamps) are not called radio lamps and usually belong to the class of lighting devices.
Operating principle
Electronic tube RCA "808"
Vacuum vacuum tubes with heated cathode
- As a result of thermionic emission, electrons leave the cathode surface.
- Under the influence of the potential difference between the anode and the cathode, electrons reach the anode and form an anode current in the external circuit.
- With the help of additional electrodes (grids), the electron flow is controlled by applying an electric potential to these electrodes.
In vacuum tubes, the presence of gas degrades the tube's performance.
Gas-filled vacuum tubes
The main thing for this class of devices is the flow of ions and electrons in the gas filling the lamp. The flow can be created, as in vacuum devices, by thermionic emission, or it can be created by the formation of an electric discharge in the gas due to the electric field strength.
Story
According to the heating method, cathodes are divided into direct and indirect heated cathodes.
The directly heated cathode is a metal filament. Directly filament lamps consume less power and heat up faster, however, they usually have a shorter service life, when used in signal circuits they require DC filament power, and are not applicable in a number of circuits due to the influence of potential differences in different sections of the cathode on the operation of the lamp.
The indirectly heated cathode is a cylinder, inside of which a filament (heater) is located. Such lamps are called indirect filament lamps.
Lamp cathodes are activated with metals that have a low work function. In direct-heat lamps, thorium is usually used for this, in indirect-heat lamps - barium. Despite the presence of thorium in the cathode, direct filament lamps do not pose a danger to the user, since its radiation does not extend beyond the cylinder.
Anode
Vacuum tube anode
Positive electrode. It is made in the form of a plate, usually a box shaped like a cylinder or parallelepiped. It is usually made from nickel or molybdenum, sometimes from tantalum and graphite.
Net
Between the cathode and anode there are grids, which serve to control the flow of electrons and eliminate side effects that occur when electrons move from the cathode to the anode.
The mesh is a lattice made of thin wire or more often made in the form of a wire spiral wound around several supporting posts (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 operation is different than in the traditional design.
Based on their purpose, meshes are divided into the following types:
Depending on the purpose of the lamp, it can have up to seven grids. In some options for switching on multi-grid lamps, individual grids can act as an anode. For example, in a generator according to the Shembel circuit on a tetrode or pentode, the generator itself is a “virtual” triode formed by a cathode, a control grid and a screening grid as an anode.
Balloon
Main types
Small-sized (“finger”) radio tubes
Main types of electronic vacuum tubes:
- Diodes (easily made for high voltages, see kenotron)
- beam tetrodes and pentodes (as variations of these types)
- combination lamps (actually include 2 or more lamps in one cylinder)
Modern Applications
Air-cooled metal-ceramic generator triode GS-9B (USSR)
High frequency and high voltage power technology
- In high-power radio broadcast transmitters (from 100 W to several megawatts), powerful and ultra-powerful lamps with air or water anode cooling and high (more than 100 A) filament current are used in the output stages. Magnetrons, klystrons, so-called. traveling wave radio tube provide a combination high frequencies, capacity and acceptable cost (and often simply the fundamental possibility of existence) of the element base.
- A magnetron can be found not only in radar, but also in any microwave oven.
- If it is necessary to rectify or quickly switch several tens of kV, which cannot be accomplished with mechanical switches, it is necessary to use radio tubes. Thus, the kenotron provides acceptable dynamics at voltages up to a million volts.
Military industry
Due to the principle of operation, vacuum tubes are devices that are much more resistant to damaging factors such as electromagnetic pulses. For information: a single device can contain several hundred lamps. In the USSR, for use in on-board military equipment in the 1950s, rod lamps were developed, characterized by their small size and high mechanical strength.
Miniature lamp of the “acorn” type (pentode 6Zh1Zh, USSR, 1955)
Space technology
Radiation degradation of semiconductor materials and the presence of a natural vacuum in the interplanetary environment make the use of certain types of lamps a means of increasing the reliability and durability of spacecraft. The use of transistors in the Luna-3 spacecraft was associated with great risk.
Increased environmental temperature and radiation
Tube equipment can be designed for a larger temperature and radiation range of conditions than semiconductor equipment.
High quality audio equipment
By subjective opinion For most music lovers, “tube” sound is fundamentally different from “transistor” sound. There are several versions of the explanation for these differences, both based on scientific research, and frankly unscientific reasoning. One of the main explanations for the differences between tube and transistor sound is the “naturalness” of the sound of tube equipment. Tube sound is “surround” (some call it “holographic”), as opposed to “flat” transistor sound. A tube amplifier clearly conveys the emotions, energy of the performer, “drive” (for which guitarists adore them). Transistor amplifiers have difficulty coping with such tasks. Often, designers of transistor amplifiers use circuitry similar to lamps (operating mode in class A, transformers, lack of common negative feedback). The overall result of these ideas was the “return” of tube technology to the field of high-quality amplifiers. The objective (scientific) reason for this situation is the high linearity (but not ideal) of the lamp, primarily the triode. A transistor, primarily a bipolar one, is a generally nonlinear element, and as a rule cannot operate without linearization measures.
Advantages of tube amplifiers:
Simplicity of circuits. Its parameters depend little on external factors. As a result, a tube amplifier typically has fewer parts than a solid-state amplifier.
The parameters of the lamps depend less on temperature than the parameters of the transistor. The lamps are insensitive to electrical overloads. The small number of parts also greatly contributes to the reliability and reduction of distortion introduced by the amplifier. The transistor amplifier has problems with thermal distortion.
Good matching of the tube amplifier input with the load. Tube stages have a very high input impedance, which reduces losses and helps reduce the number of active elements in the radio device. - Easy to maintain. If, for example, a lamp in a concert amplifier breaks down right during a performance, then replacing it is much easier than replacing a burnt-out transistor or microcircuit. But no one does this at concerts anyway. There is always a supply of amplifiers at concerts, and a double supply of tube amplifiers (because, oddly enough, tube amplifiers break down much more often).
The absence of certain types of distortion inherent in transistor stages, which has a beneficial effect on the sound.
With proper use of the advantages of tubes, it is possible to create amplifiers that surpass transistor ones in sound quality within certain price categories.
Subjectively vintage appearance when creating image equipment samples.
Insensitive to radiation up to very high levels.
Disadvantages of tube amplifiers:
In addition to powering the anodes, lamps require additional power consumption for heating. Hence the low efficiency, and as a result - strong heating.
Lamp equipment cannot be immediately ready for use. Pre-heating of the lamps for several tens of seconds is required. The exception is direct filament lamps, which start working immediately.
The output tube stages must be matched to the load using transformers. As a consequence, the complexity of the design and poor weight and dimensions due to transformers.
Tubes require the use of high supply voltages, amounting to hundreds (and in powerful amplifiers, thousands) of volts. This imposes certain restrictions in terms of safety when operating such amplifiers. Also, high pickup voltage almost always requires the use of a step-down output transformer. Moreover, any transformer is a nonlinear device in a wide frequency range, which causes the introduction of nonlinear distortions into the sound at a level close to 1% best models tube amplifiers (by comparison, the nonlinear distortion of the best transistor amplifiers is so small that it cannot be measured). For a tube amplifier, distortion of 2-3% can be considered normal. The nature and spectrum of these distortions differs from the distortions of a transistor amplifier. This usually has no effect on subjective perception. A transformer is, of course, a nonlinear element. But it is very often used at the output of a DAC, where it provides galvanic isolation (prevents the penetration of interference from the DAC), plays the role of a band-limiting filter, and apparently ensures the correct “alignment” of signal phases. As a result, despite all the disadvantages (primarily the high cost), the sound only benefits. Also, transformers are often successfully used in transistor amplifiers.
Lamps have a limited service life. Over time, the parameters of the lamps change, the cathodes lose emission (the ability to emit electrons), and the filament can burn out (most lamps operate for 200-1000 hours before failure, transistors are three orders of magnitude longer). Transistors can also degrade over time.
The fragility of classic glass bulb lamps. One of the solutions to this problem was the development in the 40s of the last century of lamps with metal-ceramic cylinders, which have greater strength, but such lamps were not widely used.
Some features of tube amplifiers:
In the subjective opinion of audiophiles, the sound of electric guitars is conveyed much better, deeper and more “musically” by tube amplifiers. Some explain this by the nonlinearity of the output node and the introduced distortions, which are “valued” by electric guitar lovers. This is actually not true. Guitarists use effects associated with increasing distortion, but to do this, appropriate changes are made to the circuit deliberately.
The obvious disadvantages of a tube amplifier are fragility, higher energy consumption than a transistor amplifier, shorter tube life, greater distortion (this is usually remembered when reading technical specifications, due to serious imperfections in measuring the main parameters of amplifiers; many manufacturers do not provide such data , or in other words - two amplifiers that are completely identical, from the point of view of measured parameters, can sound completely different), large dimensions and weight of the equipment, as well as a cost that is higher than that of transistor and integrated technology. The energy consumption of a high-quality transistor amplifier is also high, although its dimensions and weight can be comparable to a tube amplifier. In general, there is such a pattern: the “soundier”, “more musical”, etc., the amplifier, the larger its dimensions and power consumption, and the lower the efficiency. Of course, a Class D amplifier can be very compact, and its efficiency will be 90%. But what to do with the sound? If you are planning a struggle to save electricity, then, of course, a tube amplifier is not an assistant in this matter.
Classification by name
Markings adopted in the USSR/Russia
Labels in other countries
In Europe in the 30s, the leading manufacturers of radio tubes adopted the Unified European Alphanumeric Labeling System:
- The first letter characterizes the filament voltage or its current:
A - filament voltage 4 V;
B - filament current 180 mA;
C - filament current 200 mA;
D - filament voltage up to 1.4 V;
E - filament voltage 6.3 V;
F - filament voltage 12.6 V;
G - filament voltage 5 V;
H - filament current 150 mA;
K - filament voltage 2 V;
P - filament current 300 mA;
U - filament current 100 mA;
V - filament current 50 mA;
X - filament current 600 mA.
- The second and subsequent letters in the designation determine the type of lamp:
B - double diodes (with a common cathode);
C - triodes (except weekends);
D - output triodes;
E - tetrodes (except weekend);
F - pentodes (except weekends);
L - output pentodes and tetrodes;
H - hexodes or heptodes (hexode type);
K - octodes or heptodes (octode type);
M - electronic light setting indicators;
P - amplification tubes with secondary emission;
Y - half-wave kenotrons;
Z - full-wave kenotrons.
- A two-digit or three-digit number indicates the external design of the lamp and the serial number of this type, with the first digit usually characterizing the type of base or leg, for example:
1-9 - glass lamps with a lamellar 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 a local base;
6x and 7x - glass subminiature lamps;
8x and from 180 to 189 - miniature glass with a nine-pin leg;
9x - glass miniatures with a seven-pin leg.
See also
Gas discharge lamps
Gas discharge lamps usually use a discharge in inert gases at low pressures. Examples of gas-discharge vacuum tubes:
- Gas arresters for protection against high voltage(for example, on overhead communication lines, powerful radar receivers, etc.)
- Thyratrons (three-electrode lamps - gas-discharge triodes, four-electrode lamps - gas-discharge tetrodes)
- Xenon, neon lamps and other gas-discharge light sources.
See also
- AOpen AX4B-533 Tube - Motherboard on Intel 845 Sk478 chipset with tube audio amplifier
- AOpen AX4GE Tube-G - Motherboard based on Intel 845GE Sk478 chipset with tube audio amplifier
- AOpen VIA VT8188A - Motherboard based on the VIA K8T400M Sk754 chipset with a 6-channel tube audio amplifier.
- Hanwas X-Tube USB Dongle - USB sound card for laptops with DTS support, simulating appearance electron tube.
Notes
Links
- Handbook of domestic and foreign radio tubes. More than 14,000 radio tubes
- Guides to radio tubes and all the necessary information
| Passive solid state | Resistor Variable resistor Trimmer resistor Varistor Capacitor Variable capacitor Trimmer capacitor Inductor Quartz resonator· Fuse · Self-resetting fuse Transformer |
|---|---|
| Active Solid State | Diode· LED · Photodiode · Semiconductor laser ·
Schottky diode· Zener diode · Stabilistor · Varicap · Varicond · Diode bridge ·
Avalanche diode ·
Tunnel diode ·
Gunn diode Transistor · Bipolar transistor · Field effect transistor · |
Computer technology is a critical component of the computing and data processing process. Over the past 50 years, more than one generation of computers has changed. And if the first four generations differed from each other only in the element base and architecture, then the never-created “fifth generation computers” were supposed to include artificial intelligence functions.
TO first generation include computers based on vacuum tubes and relays (40s of the 20th century). RAM was performed on triggers, later on ferrite cores. The use of a vacuum tube as the main element of a computer created many problems. Due to the fact that the height of the glass lamp is 7 cm, the machines were huge. Every 7-8 minutes one of the lamps failed, and since there were 15-20 thousand of them in the computer, it took a lot of time to find and replace the damaged lamp. The performance of such computing systems is 5-30 thousand arithmetic operations per second. The data was entered into the computer memory by connecting the required plug to the desired socket. Such computers were used mainly for scientific and technical calculations.
On July 1, 1948, Bell Telephone Laboratories developed an electronic device that could replace the vacuum tube - the transistor. This event can be considered the beginning of computers second generation. The first transistor-based computers appeared in the late 50s, and by the mid-60s more compact external devices were created, which allowed Digital Equipment to release the first mini-computer PDP-8 in 1965, the size of a refrigerator and costing only 20 thousand dollars.
The use of transistors as the main element in computers has led to a reduction in the size of computers by hundreds of times and to an increase in their reliability. The most important difference between a transistor is that it alone replaces 40 vacuum tubes and at the same time operates at a higher speed, generates very little heat and consumes almost no electricity.
The advent of integrated circuits heralded the advent of machines third generation. An integrated circuit is a miniature electronic circuit an area of about 10 square millimeters. An integrated circuit can replace thousands of transistors, each of which in turn has already replaced 40 vacuum tubes. Become part of the computer operating systems. Many tasks of managing memory, input/output devices and other resources began to be taken over by the OS or directly by the computer hardware. Added to all the advantages of third-generation computers was the fact that their production turned out to be cheaper than the production of second-generation machines. Thanks to this, many organizations were able to purchase and use such machines. Most of the computers created before were specialized machines that could solve problems of one type.
The arrival of the computer fourth generation associated with the transition of integrated circuits to large-scale integrated circuits and ultra-large-scale integrated circuits. The element base has made it possible to achieve great success in minimizing the size, increasing the reliability and performance of computers. First personal computers can be considered Altair-8800, created on the basis of Intel-8080, in 1974. The face of the 4th generation is largely determined by the creation of supercomputers characterized by high performance. Supercomputers are used in solving problems of mathematical physics, cosmology and astronomy, modeling complex systems etc.
Term fifth generation computers is nothing more than a large-scale government program in Japan to develop the computer industry and artificial intelligence, undertaken in the 1980s. The goal of the program was to create a “landmark computer” with supercomputer performance and powerful artificial intelligence capabilities. It was expected to achieve a significant breakthrough in the field of solving applied problems of artificial intelligence. In particular, the following problems had to be solved:
- creation of an automatic portable translator from language to language (directly from voice);
- automatic abstracting of articles, search for meaning and categorization
- recognition tasks, etc.
The idea of self-development of the system, according to which the system itself should change its internal rules and parameters, turned out to be unproductive - the system, passing through a certain point, slipped into a state of loss of reliability and loss of integrity, sharply “stupid” and became inadequate. Over ten years, more than $500 million was spent on development, and the program ended without achieving its goal. To date, the project is considered an absolute failure.
How are the designations of lamps deciphered, how are the names of lamps formed, what is the difference between multi-grid and multi-electrode lamps, how are the electrodes of receiving lamps routed, etc.
How are lamp designations deciphered?
Reception lamps produced by the Svetlana plant are usually designated by two letters and a number. The first letter indicates the purpose of the lamp, the second - the type of cathode, and the number - the serial number of the development of the lamp.
The letters are deciphered as follows:
- U - intensifying,
- P - reception,
- T - translational,
- G - generator,
- F - low-power generator (old name),
- M - modulatory,
- B - powerful generator (old name)
- K - kenotron,
- B - rectifier,
- S - special.
The type of cathode is indicated by the following letters:
- T - thoriated,
- O - oxidized,
- K - carbonated,
- B - barium.
Thus CO-124 means: special oxide No. 124.
In generator lamps, the number next to the letter G indicates the useful output power of the lamp, and for low-power lamps (with natural cooling) this power is indicated in watts, and for water-cooled lamps - in kilowatts.
What do the letters “C” and “RL” on the cylinders of our radio tubes mean?
The letter “S” in the circle is a brand of the Leningrad plant “Svetlana”, “RL” is a brand of the Moscow plant “Radiolampa”.
How are lamp names formed?
All modern radio tubes can be divided into two categories: single lamps, which have one lamp in their cylinder, and combined lamps, which are a combination of two or more lamps, sometimes having one (common) and sometimes several independent cathodes.
For lamps of the first type, there are two ways of composing names. The names compiled according to the first method indicate the number of grids, with the number of grids indicated by the Greek word, and the grid by the English word (grid).
Thus, according to this method, a five-grid lamp will be called a “pentagrid”. According to the second method, the name indicates the number of electrodes, of which one is a cathode, the other an anode, and all the rest are grids.
A lamp with only two electrodes (anode and cathode) is called a diode, a three-electrode is a triode, a four-electrode is a tetrode, a five-electrode is a pentode, a six-electrode is a hexode, a seven-electrode is a heptode, and an eight-electrode is an octode.
Thus, a lamp having seven electrodes (anode, cathode and five grids) can be called a pentagrid in one way, and a heptode in another.
Combined lamps have names indicating the types of lamps enclosed in one cylinder, for example: diode-pentode, diode-triode, double diode-triode (the latter name indicates that two diode lamps and one triode are enclosed in one cylinder).
What is the difference between multi-grid and multi-electrode lamps?
Recently, in connection with the production of lamps with many electrodes, the following classification of lamps, which has not yet received general recognition, has been proposed.
It is proposed to call multigrid lamps those lamps that have one cathode, one anode and several grids. Multi-electrode lamps are those that have two or more anodes. A multi-electrode lamp will also be called one that has two or more cathodes.
The shielded lamp, pentode, pentagrid, octode are multi-grid, since each of them has one anode and one cathode and, respectively, two, three, five and six grids.
The same lamps as double diode-triode, triode-pentode, etc. are considered multi-electrode, since the double diode-triode has three anodes, the triode-pentode has two anodes, etc.
What is a variable slope lamp?
Tubes with variable slope have the distinctive feature that their characteristic at small biases near zero has a large slope and the gain increases to a maximum.
As negative bias increases, the slope and gain of the tube decrease. This property of a lamp with a variable slope allows it to be used in the high-frequency amplification stage of the receiver to automatically adjust the reception strength: with weak signals (the bias is small), the lamp amplifies to the maximum, with strong signals the gain drops.
The figure on the left shows the characteristics of the 6SK7 variable slope lamp and on the right the characteristics of the conventional 6SJ7 lamp. A distinctive feature of a lamp with variable slope is the long “tail” at the bottom of the characteristic.
Rice. 1. Characteristics of a lamp with variable slope 6SK7 and on the right the characteristic of a regular lamp 6SJ7.
What do DDT and DDP mean?
DDT is the short name for dual diode-triode, and DDP is the short name for double diode-pentode.
The electrode terminals for various lamps are shown in the figure. (The pin markings are given as if you were looking at the base from below).
Rice. 2. How the electrodes of the receiving lamps are routed.
- 1 - direct filament triode;
- 2 - shielded direct filament lamp;
- 3 - two-anode kenotron;
- 4 - direct filament pentode;
- 5 - indirect filament triode;
- 6 - shielded lamp with indirect heat;
- 7 - direct filament pentagrid;
- 8 - indirect filament pentagrid;
- 9 - direct filament double triode;
- 10 - double direct filament diode-triode;
- 11 - double diode-triode indirect filament;
- 12 - indirectly heated pentode;
- 13 - double pentode diode with indirect heating;
- 14 - powerful triode;
- 15 - powerful single-anode kenotron.
What are the lamp parameters?
Each vacuum tube has some distinctive features, characterizing its suitability for operation under known conditions, and the gain that this lamp can provide.
These lamp-specific data are called its parameters. The main parameters include: lamp gain, slope, internal resistance, quality factor, value of interelectrode capacitance.
What is gain?
The gain (usually denoted by the Greek letter |i) shows how many times stronger, compared to the action of the anode, the effect of the control grid on the flow of electrons emitted by the filament.
The all-Union standard 7768 defines gain as “a parameter of a vacuum tube that expresses the ratio of the change in the anode voltage to the corresponding inverse change in the grid voltage necessary to ensure that the value of the anode current remains constant.”
What is the slope of the characteristic?
The slope of the characteristic is the ratio of the change in the anode current to the corresponding change in the voltage of the control grid at a constant voltage at the anode.
The slope of the characteristic is usually designated by the letter S and is expressed in milliamperes per volt (mA/V). The slope of the characteristic is one of the most important parameters lamps. We can assume that the greater the steepness, the better the lamp.
What is the internal resistance of a lamp?
The internal resistance of the lamp is the ratio of the change in anode voltage to the corresponding change in anode current at a constant voltage on the grid. Internal resistance is designated by the letter Shi and is expressed in ohms.
What is the quality factor of a lamp?
The quality factor is the product of the gain and the slope of the lamp, i.e. the product of i and S. The quality factor is denoted by the letter G. The quality factor characterizes the lamp as a whole.
The higher the quality factor of the lamp, the better the lamp. Quality factor is expressed in milliwatts divided by volts squared (mW/V2).
What is the internal equation of a lamp?
The internal equation of the lamp (it is always equal to 1) is the ratio of the slope of the characteristic S, multiplied by the internal resistance Ri and divided by the gain c, i.e. S*Ri/c=1.
Hence: S=ts/Ri, ts=S*Ri, Ri=ts/S.
What is interelectrode capacitance?
Interelectrode capacitance is the electrostatic capacitance that exists between the different electrodes of the lamp, for example, between the anode and the cathode, the anode and the grid, etc.
The capacitance between the anode and the control grid (Cga) is of greatest importance, as it limits the gain that can be obtained from the tube. In shielded lamps designed to amplify high frequencies, Cga is usually measured in hundredths or thousandths of a micromicrofarad.
What is the input capacitance of a lamp?
The input capacitance of the lamp (Cgf) is the capacitance between the control grid and the cathode. This capacitance is usually connected to the capacitance of the variable capacitor of the tuning circuit and reduces the overlap of the circuit.
What is power dissipation at the anode?
During operation of the lamp, a stream of electrons flies to the anode. The impact of electrons on the anode causes the latter to heat up. If you dissipate (release) a lot of power at the anode, the anode may melt, which will lead to the death of the lamp.
The power dissipation at the anode is the maximum power for which the anode of a given lamp is designed. This power is numerically equal to the anode voltage multiplied by the anode current and is expressed in watts.
If, for example, an anode current of 20 mA flows through a lamp at an anode voltage of 200 V, then 200 * 0.02 = 4 W is dissipated at the anode.
How to determine the power dissipation at the lamp anode?
The maximum power that can be dissipated at the anode is usually indicated in the lamp data sheet. Knowing the dissipation power and setting a certain anode voltage, you can calculate what maximum current is permissible for a given lamp.
Thus, the power dissipation at the anode of the UO-104 lamp is 10 W. Therefore, with an anode voltage of 250 V, the anode current of the lamp should not exceed 40 mA, since at such a voltage exactly 10 W will be dissipated at the anode.
Why does the anode of the output lamp become hot?
The anode of the output lamp becomes hot because it releases more power than the lamp is designed for. This usually occurs in cases where a high voltage is applied to the anode, and the bias set to the control grid is small; in this case, a large anode current flows through the lamp, and as a result, the dissipation power exceeds the permissible one.
To avoid this phenomenon, it is necessary to either reduce the anode voltage or increase the bias on the control grid. In the same way, in a lamp it is not the anode that can become hot, but the grid.
For example, sometimes shielding meshes in shielded lamps and pentodes become heated. This can happen both when the anode voltage on these lamps is too high and when the bias on the control grids is too low, and in cases where, due to some error, the anode voltage does not reach the anode of the lamp.
In these cases, a significant part of the lamp current rushes through the grid and heats it up.
Why have lamp anodes been made black recently?
Lamp anodes are blackened for better heat transfer. A blackened anode can dissipate more power.
How to understand the instrument readings when testing a purchased radio tube in a store?
The testing equipment used in radio shops to check purchased lamps is extremely primitive and does not give a true idea of the suitability of the lamp for work.
All these installations are most often designed for testing three-electrode lamps. Shielded lamps or high-frequency pentodes are tested in the same panels and therefore the test setup instruments do not show the current of the lamp anode, but the current of the shielding grid, since a shielding grid is connected to the anode pin on the base of such lamps.
Thus, if the lamp has a short circuit between the shielding mesh and the anode, then this fault will not be detected at the test facility in the store and the lamp will be considered suitable. Using these devices, one can only judge that the filament is intact and there is emission.
Can the integrity of its filament be a sign of a lamp's serviceability?
The integrity of the filament can be considered a relatively reliable sign of the suitability of the lamp for operation only in relation to lamps with a purely tungsten cathode (such lamps include, for example, the R-5 lamp, which is currently out of production).
For heated lamps and modern directly heated lamps, the integrity of the filament does not yet indicate that the lamp is suitable for use, since the lamp may not have any emission even with an intact filament.
In addition, the integrity of the filament and even the presence of emission does not mean that the lamp is completely suitable for use, because the lamp may contain short circuits between the anode and the grid, etc.
What is the difference between a full-fledged lamp and an inferior one?
At lamp factories, all lamps are checked and inspected before leaving the factory. Factory standards provide for known tolerances for lamp parameters, and lamps that meet these tolerances, i.e. lamps whose parameters do not fall outside these tolerances, are considered full-fledged lamps.
A lamp in which at least one of the parameters falls outside these tolerances is considered defective. Defective lamps also include lamps that have external defects, for example, crooked electrodes, a crooked cylinder, cracks, scratches on the base, etc.
Lamps of this kind are labeled “defective” or “2nd grade” and are sold at a reduced price. Usually, defective lamps are not much different from full ones in terms of performance.
When purchasing defective lamps, it is advisable to choose one that has an obvious external defect, since such a defective lamp almost always has completely normal parameters.
What is the cathode of a lamp?
The lamp cathode is the electrode that, when heated, emits electrons, the flow of which forms the anode current of the lamp.
In direct-fired lamps, electrons are emitted directly from the filament. Consequently, in directly heated lamps the filament is also the cathode. Such lamps include UO-104 lamps, all barium lamps, and kenotrons.
Rice. 3. What are direct filament lamps?
In a heating lamp, the filament is not its cathode, but is used only to heat the porcelain cylinder inside which this filament passes to the required temperature.
A nickel case with a special active layer applied to it is placed on this cylinder, emitting electrons when heated. This electron-emitting layer is the cathode of the lamp.
Due to the large thermal inertia of the porcelain cylinder, it does not have time to cool down during changes in the direction of the current and therefore the alternating current background will be practically not noticeable when the receiver is operating.
Heated lamps are otherwise called indirectly heated or indirectly heated lamps, as well as lamps with an equipotential cathode.
Rice. 4. What is a heated lamp.
Why do they make lamps with indirect filament, when it would be easier to make lamps with direct filament and thick filament?
If a direct filament lamp is heated with alternating current, then an alternating current noise is usually heard. This noise is largely explained by the fact that when the direction of the current changes and when the current drops to zero at these moments, the lamp filament cools somewhat and its emission decreases.
It would seem possible to avoid AC noise by making the filament very thick, since a thick filament will not have time to cool significantly.
However, in practice it is very unprofitable to use lamps with such filaments, since they will consume a very large current for heating. In addition, it should be noted that the alternating current background, when powering the filament, occurs not only due to periodic cooling of the filament.
The background also depends to a certain extent on the fact that the potential of the filament changes its sign 50 times per minute, and since the lamp grid in the circuit is connected to the filament, this change in direction is transmitted to the grid, causing a pulsation of the anode current, which is heard in the loudspeaker as a background.
Therefore, it is much more profitable to make lamps with indirect heating, since such lamps are free from the listed disadvantages.
What is an equipotential cathode?
An equipotential cathode is a heated cathode. The name “equipotential” is used because the potential along the entire length of the cathode is the same.
In direct heated cathodes the potential is not the same: it varies in 4-volt lamps from 0 to 4 V, in 2-volt lamps from 0 to 2 V.
What is a cathode activated lamp?
Electron tubes previously had a purely tungsten cathode. Significant emission from these cathodes begins only at very high temperatures (about 2,400°).
To create this temperature, a strong current is needed and thus lamps with a tungsten cathode are very uneconomical. It was noticed that when the cathodes are coated with oxides of the so-called alkaline earth metals, emission from the cathodes begins at a much lower temperature (800-1,200°) and therefore, for the corresponding incandescence of the lamp, a much weaker current is needed, i.e. such a lamp becomes more economical in the consumption of batteries or accumulators.
Such cathodes coated with oxides of alkaline earth metals are called activated, and the process of such coating is called cathode activation. The most common activator currently is barium.
What is the difference between thoriated, carbonated, oxide and barium lamps?
The difference between these types of lamps lies in the method of processing (activation) of the cathodes of the lamps. To increase the emissivity, the cathode is coated with a layer of thorium, oxide, and barium.
Lamps with a cathode coated with thorium are called thoriated. Lamps coated with a layer of barium are called barium lamps. Oxide lamps are also, in most cases, barium lamps, and the difference in their name is explained only by the way the cathode is activated.
For some (high-power) lamps, to firmly secure the thorium layer, the cathode is treated with carbon after activation. These types of lamps are called carbonated.
Is it possible to judge by the color of the lamp whether the lamp mode is correct?
Within certain limits, the color of the glow can be used to judge the correctness of the lamp's filament value, but this requires a certain amount of experience, since lamps different types have unequal cathode glow.
Is heating the lamp base dangerous?
Heating of the lamp base during operation does not pose any danger to the lamp and is explained by the transfer of heat from the cylinder and internal parts of the lamp to the base.
Why is a mica disk placed inside the cylinder against the base in some lamps (for example, UO-104)?
This mica disk serves to protect the base from thermal radiation from the lamp electrodes. Without such a “thermal shield”, the lamp base would become too hot. Similar thermal screens are used in all high-power lamps.
Why do you hear something rolling around inside the base when you turn some lamps over?
Such rolling occurs due to the fact that when pinning the lamps, insulators are put on the conductors that are inside the base and connect the electrodes to the pins - glass tubes that protect the output conductors from shorting with each other.
These tubes in some lamps move along the wire when the lamps are turned over.
Why are the cylinders of modern lamps stepped?
In old-type lamps, the electrodes were fixed only on one side, in the place of the lamp where the stands on which the electrodes are mounted are connected to the glass leg.
With this mounting design, due to the elasticity of the holders, the electrodes are easily subject to vibration. In the cylinders of modern lamps, the electrodes are fastened at two points - at the bottom they are attached with holders to the glass leg, and at the top - to the mica plate, which is pressed into the “dome” of the lamp.
Thus, the entire lamp structure becomes more reliable and rigid, which increases the longevity of the lamps when they have to work, for example, in moving parts, etc. Lamps of this design are less prone to microphonic effects.
Why are lamp cylinders covered with a silver or brown coating?
For normal operation of the lamps, the degree of rarefaction of the air inside the cylinder (vacuum) must be very high. The pressure in the lamp is measured in millionths of a millimeter of mercury.
It is extremely difficult to obtain such a vacuum using the most advanced pumps. But this vacuum does not yet protect the lamp from deterioration of the vacuum in the future.
The metal from which the anode and mesh are made may contain absorbed (“occluded”) gas, which, when the lamp is operated and the anode is heated, can then be released and worsen the vacuum.
To combat this phenomenon, when pumping out the lamp, it is introduced into a high-frequency field, which heats up the electrodes of the lamp. Even before this, a so-called “getter” (absorber), i.e., substances such as magnesium or barium that have the ability to absorb gases, is introduced into the balloon in advance.
Sprayed under the influence of a high-frequency field, these substances absorb gases. The sprayed getter is deposited on the lamp cylinder and covers it with a coating visible from the outside.
If magnesium was used as a getter, then the balloon has a silver tint; with a barium getter, the coating turns out to be golden brown.
Why do the lamps glow blue?
Most often, the lamp gives a blue gas glow because gas has appeared in the lamp. In this case, if you turn on the lamp and apply voltage to its anode, the entire lamp cylinder is filled with blue light.
This lamp is not suitable for use. Sometimes, when the lamp is operating, the surface of the anode begins to glow. The reason for this phenomenon is the settling of the active layer on the anode and grid of the lamp during activation of the cathode.
In this case, only inner surface anode. This phenomenon does not prevent the lamp from working normally and is not a sign of damage.
How does the presence of gas in a lamp affect its operation?
If there is gas in the lamp cylinder, ionization of this gas occurs during operation. The ionization process is as follows: electrons rushing from the cathode to the anode meet gas molecules on their way, hit them and knock electrons out of them.
The knocked-out electrons, in turn, rush to the anode and increase the anode current, and this increase in the anode current occurs unevenly, intermittently, and worsens the operation of the lamp.
Those gas molecules from which electrons have been knocked out and resulting in positive charges (so-called ions) rush to the negatively charged cathode and hit it.
With significant amounts of gas in the lamp, ion bombardment of the cathode can lead to the active layer being knocked off it, and even to burnout of the cathode.
Positively charged ions are also deposited on the grid, which has a negative potential, and form the so-called ion grid current, the direction of which is opposite to the usual grid current of the lamp.
This ion current significantly worsens the performance of the cascade, reducing the gain and sometimes introducing distortion.
What is thermionic current?
Electrons located in the mass of a body are constantly in motion. However, the speed of this movement is so low that electrons cannot overcome the resistance of the surface layer of the material and fly beyond it.
If the body is heated, then the speed of movement of the electrons will increase and ultimately can reach such a limit that the electrons will fly out of the body.
Such electrons, the appearance of which is due to the heating of the body, are called thermionic electrons, and the current formed by these electrons is called thermionic current.
What is emission?
Emission is the emission of electrons from the lamp cathode.
When does a lamp lose emission?
Loss of emission is observed only for lamps with an activated cathode. The loss of emission is a consequence of the disappearance of the active layer, which can occur due to various reasons, for example, from overheating when applying a higher filament voltage than normal, as well as in the presence of gas in the cylinder and the resulting ion bombardment of the cathode (see question 125).
What is the receiver lamp mode called?
The operating mode of the lamp is the complex of all constant voltages that are supplied to the lamp, i.e. filament voltage, anode voltage, voltage on the shielding grid, bias on the control grid, etc.
If all these voltages correspond to the voltages required for a given lamp, then the lamp is operating in the correct mode.
What does it mean to put the lamp in the desired operating mode?
This means that all electrodes must be supplied with voltages that correspond to those specified in the lamp passport or in the instructions.
If the description of the receiver does not contain special instructions about the lamp mode, then you should be guided by the mode data given in the lamp data sheet.
What does the expression “lamp locked” mean?
By “blocking” the lamp is meant the case when such a large negative potential is created on the control grid of the lamp that the anode current stops.
This locking can occur if there is too much negative bias on the lamp grid, or if there is an open circuit in the lamp grid. In this case, the electrons deposited on the grid do not have the opportunity to flow to the cathode and this “locks” the lamp.
Electronic tubes can be classified according to the number of electrodes, purpose, frequency range, power, cathode type, and dimensions.
Depending on the number of electrodes, electronic tubes are divided into diodes, triodes, tetrodes, pentodes, heptodes, combined tubes (double diodes, double triodes, triode-pentodes, triode-heptodes, etc.).
Depending on the functions performed, lamps can be rectifying, detecting, amplifying, converting, generating, etc.
A diode is an electron tube with two electrodes: an anode and a cathode. It was invented by John Fleming in 1904. The cathode is located in the center of the lamp: the anode, shaped like a cylinder, encloses the cathode. The principle of operation of the diode is as follows. If a positive potential is applied to the anode, then the negatively charged electrons emitted from the cathode under the influence of an electric field will rush to the positive anode, forming a continuous electron flow that closes electrical circuit anode power source. Anode current I a will flow in the external circuit. Since the positive direction of the current is conventionally taken to be the direction from plus to minus of the current source, then inside the diode the current flows from the anode to the cathode, i.e., against the movement of electrons. The magnitude of the anode current is determined by the number of electrons flying from the cathode to the anode per unit time.
If you connect the minus of the current source to the anode of the diode, and the plus to the cathode, then the negatively charged anode will repel negative electrons back to the cathode. In this case, no current will flow through the lamp. Therefore, the diode conducts electric current only in one direction - from the anode to the cathode, when the anode potential is higher than the cathode potential.
One-way conductivity of a diode is its main property. It is this property that determines the purpose of the diode - rectifying alternating currents into direct currents and converting high-frequency modulated oscillations into audio frequency currents (detection).
Diodes designed to rectify alternating current are called kenotrons. They are marked with the letter C (1Ц1С, 1Ц7С, 1Ц11П, 1Ц21П, ЗЦ18П, 5ЦЗС, 6Ц4П, etc.).
Diodes intended for detection are low-power. They are most often produced as dual-anode lamps or as part of combined lamps. These diodes are marked with the letter X or D (6D14P, 6D20P, 6X6S).
A triode is an electron tube in which a third electrode, a grid, is placed between the anode and cathode. This lamp was proposed in 1906 by the American scientist Lee de Forest. The grid in modern lamps is made in the form of a wire spiral surrounding the cathode. The mesh is made from nickel, molybdenum or tungsten. The triode grid is called a control grid, since it can be used to easily control the anode current density by applying a positive or negative voltage of a certain value to the grid.
Given that the grid in the triode is located closer to the cathode than the anode, its effect on the electron flow will be more significant. This property of the triode is widely used in radio engineering to amplify weakened radio signals. The principle of radio signal amplification comes down to the following. The signal to be amplified is fed to the triode control grid. A change in the grid potential will lead to a corresponding change in the anode current. In this case, the amplified voltage of the signal supplied to the grid will be removed from the anode. A constant negative potential (grid bias voltage) is applied to the grid of such a magnitude that positive half-cycles of the signal do not create a positive voltage on the grid. Otherwise, a grid current appears (the positive grid will attract some electrons), as a result, the anode current decreases, which leads to signal distortion.
Triodes are used as amplifiers of low and high frequencies, to generate various pulse shapes in a wide frequency range, and to match circuits (cathode followers). The marking of triodes contains the letter S or N (double triodes) 6N1P, 6NZP, 6N7S, 6N9S, 6N24P, etc.
To determine the possibility of using triodes and multi-electrode lamps in general in a particular circuit, use technical characteristics(parameters) of the lamp, the most important of which are: slope, gain and internal resistance of the lamp.
The slope of the characteristic S is a value showing how many milliamps the anode current will change when the voltage on the grid changes by 1 V and the voltage on the anode remains constant. It is defined as the ratio of the anode current increment AI a to the grid voltage increment AU C
The gain determines the amplifying properties of the lamps. It represents the ratio of the anode voltage increment AU a to the grid voltage increment AU C , which cause the same increment in the anode current AI a
The internal resistance of the triode Ri is the resistance between the anode and the cathode for the alternating current of the anode. It is expressed as the ratio of the increment in anode voltage AU a to the increment in anode current AI a
If the transconductance evaluates the effect of the grid voltage on the anode current, then the internal resistance allows us to evaluate the effect of the anode voltage on the anode current.
A tetrode is a four-electrode lamp with two grids, one of which is control, the other is shielding. The latter is placed between the control grid and the anode to increase the gain of the lamp. A positive voltage equal to 50-80% of the anode voltage is applied to the shielding grid. Under these conditions, electrons under the influence of two accelerating fields (anode and second grid) develop high speed and knock out secondary electrons from the anode, which move from it to the screening grid and are attracted by it. This phenomenon is called the dynatron effect in the tetrode. It leads to an increase in the shielding grid current and a decrease in the anode current, which is equivalent to distortion of the amplifying signal.
To eliminate the harmful influence of the dynatron effect, a retarding negative field is created in the gap between the shielding mesh and the anode. For this purpose, two metal plates connected to the cathode are placed between the grid and the anode. Such lamps are called beam tetrodes. They are widely used as final amplifiers low frequency signals (6P13S, 6P31S, 6P36S, 6P1P).
The second way to eliminate the dynatron effect in a tetrode is to introduce another grid, which is called a protective or anti-dynatron grid. A lamp with five electrodes is called a pentode. The third grid is connected to the cathode. It creates a retarding field for secondary electrons emitted from the anode and returns them back to the anode. Pentodes are the best amplification tubes; the gain for some types of pentodes reaches several thousand. They are used as amplifiers of high and intermediate frequencies.
A heptode is a seven-electrode electron tube with five grids. The purpose of the grids can be as follows: the first and third are control grids, the second and fourth are screening grids, the fifth are anti-dynatron grids. Heptodes are used to convert electrical vibrations of one frequency into vibrations of another. For example, in superheterodyne receivers they act as a converter of high-frequency oscillations of the received signal into intermediate-frequency signals.
In modern radio equipment, combined lamps are widely used, in which two or three lamps are placed in one cylinder and have their own separate electrode systems. The advantage of such lamps is obvious: they reduce the size of radio equipment and increase its efficiency. The domestic industry produces the following combined lamps: double diodes, double triodes, diode-triodes, diode-pentodes, triode-pentodes, etc. (6I1P, 6F1P, 6FZP, etc.).