An early solid-state electrical switching and amplifying device called a saturable reactor exploits saturation of the core as a means of stopping the inductive transfer of current via the core.
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279-282 It was used in a few shortwave receivers in the 1930s, and is used today in a few cheap high frequency applications such as walkie-talkies and garage door openers. In the regenerative receiver the loop gain of the feedback loop was less than one, so the tube (or other amplifying device) did not oscillate but was close to oscillation, giving large gain. In the superregenerative receiver, the loop gain was made equal to one, so the amplifying device actually began to oscillate, but the oscillations were interrupted periodically. This allowed a single tube to produce gains of over 106.
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As with all electronic oscillation, motorboating occurs when some of the output energy from an amplifying device like a transistor or vacuum tube gets coupled back into the input circuit of the device (or possibly into an earlier stage of the amplifier circuit) with the proper phase for positive feedback. This indicates there is an unwanted feedback path through the circuit from output to input of an amplifying stage. The technical conditions for oscillation, given by the Barkhausen stability criterion, are that the total gain around the feedback loop (comprising the amplifying device and the feedback path) at the oscillation frequency must be one (0 dB), and that the phase shift must be a multiple of 360° (2π radians). Since most amplifying devices, transistors and tubes, are inverting, with the output signal 180° opposite in phase from the input, the feedback path must contribute the other 180° of shift.
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Power amplifier circuits (output stages) are classified as A, B, AB and C for analog designs—and class D and E for switching designs. The power amplifier classes are based on the proportion of each input cycle (conduction angle) during which an amplifying device passes current. The image of the conduction angle derives from amplifying a sinusoidal signal. If the device is always on, the conducting angle is 360°.
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Where printed circuit boards are used, high- and low-power stages are separated and ground return traces are arranged so that heavy currents don't flow in mutually shared portions of the ground trace. In some cases the problem may only be solved by introduction of another feedback neutralization network, calculated and adjusted to eliminate the negative feedback within the passband of the amplifying device. A classic example is the Neutrodyne circuit used in tuned radio frequency receivers.
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The difference frequency, typically 400 to 1000 Hertz, is in the audio range; so it is heard as a tone in the receiver's speaker whenever the station's signal is present. Demodulation of a signal in this manner, by use of a single amplifying device as oscillator and mixer simultaneously, is known as autodyne receptionSignal Corps U.S. Army, 1922, p. 503. The term autodyne predates multigrid tubes and is not applied to use of tubes specifically designed for frequency conversion.
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It allowed radio receivers to have a single tube holder. Early concepts of an integrated circuit go back to 1949, when German engineer Werner Jacobi (Siemens AG) filed a patent for an integrated-circuit-like semiconductor amplifying device showing five transistors on a common substrate in a three-stage amplifier arrangement. Jacobi disclosed small and cheap hearing aids as typical industrial applications of his patent. An immediate commercial use of his patent has not been reported.
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Old undamped moving iron speakers have a characteristic sound, with probably the worst sound quality of any type of speaker usable for speech. Modern damped moving iron mechanisms can provide respectable sound quality, and are used in headphones. The first moving iron transducer, the telephone receiver or earphone, evolved with the first telephone systems in the 1870s. Moving iron horn loudspeakers developed from earphones after the first amplifying device which could drive a speaker, the triode vacuum tube, was perfected around 1913.
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The simplest valve (named diode because it had two electrodes) was invented by John Ambrose Fleming while working for the Marconi Company in London in 1904. The diode conducted electricity in one direction only and was used as a radio detector and a rectifier. In 1906 Lee De Forest added a third electrode and invented the first electronic amplifying device, the triode, which he named the Audion. This additional control grid modulates the current that flows between cathode and anode.
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Vacuum tubes remained the preferred amplifying device for 40 years, until researchers working for William Shockley at Bell Labs invented the transistor in 1947. In the following years, transistors made small portable radios, or transistor radios, possible as well as allowing more powerful mainframe computers to be built. Transistors were smaller and required lower voltages than vacuum tubes to work. Before the invention of the integrated circuit in 1959, electronic circuits were constructed from discrete components that could be manipulated by hand.
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The X mark is also contagious: it can be spread from one person to another, allowing other people to become Revolutor. Keroro then orders Kururu to create an amplifying device, planning to use his new power to send amplified orders to the Revolutor of Earth, putting them under his control. That night, the white Keronian (who has taken residence on a tower) sends out a strange signal. The next day, everyone has become depressed, this is because the Revolutor can sense each other's malicious thoughts, they're avoiding others, and begin to withdraw from society.
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Early in his presidency, Reagan started wearing a custom-made, technologically advanced hearing aid, first in his right ear and later in his left ear as well. His decision to go public in 1983 regarding his wearing the small, audio- amplifying device boosted their sales. On July 13, 1985, Reagan underwent surgery at Bethesda Naval Hospital to remove cancerous polyps from his colon. He relinquished presidential power to the vice president for eight hours in a similar procedure as outlined in the 25th Amendment, which he specifically avoided invoking.
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For this example, the OP1dB is approximately 2 Watts because at that input power level, the green curve is at 6 Watts and the red curve is at approximately 5 Watts. The ratio of 5/6 is 83.3%, whereas a 1 dB loss is a ratio of 79.4% = (10^{-1/10}) Gain compression is a reduction in "differential" or "slope" gain caused by nonlinearity of the transfer function of the amplifying device. This nonlinearity may be caused by heat due to power dissipation or by overdriving the active device beyond its linear region. It is a large-signal phenomenon of circuits.
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Distortion levels in early amplifiers were high, usually around 5%, until 1934, when Harold Black developed negative feedback; this allowed the distortion levels to be greatly reduced, at the cost of lower gain. Other advances in the theory of amplification were made by Harry Nyquist and Hendrik Wade Bode. The vacuum tube was virtually the only amplifying device, other than specialized power devices such as the magnetic amplifier and amplidyne, for 40 years. Power control circuitry used magnetic amplifiers until the latter half of the twentieth century when power semiconductor devices became more economical, with higher operating speeds.
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Many electronic circuits, especially amplifiers, incorporate negative feedback. This reduces their gain, but improves their linearity, input impedance, output impedance, and bandwidth, and stabilises all of these parameters, including the closed-loop gain. These parameters also become less dependent on the details of the amplifying device itself, and more dependent on the feedback components, which are less likely to vary with manufacturing tolerance, age and temperature. The difference between positive and negative feedback for AC signals is one of phase: if the signal is fed back out of phase, the feedback is negative and if it is in phase the feedback is positive.
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In addition, since the IF filters are fixed-tuned, the receiver's selectivity is the same across the receiver's entire frequency band. Another advantage is that the IF signal can be at a much lower frequency than the incoming radio signal, and that allows each stage of the IF amplifier to provide more gain. To first order, an amplifying device has a fixed gain-bandwidth product. If the device has a gain-bandwidth product of 60 MHz, then it can provide a voltage gain of 3 at an RF of 20 MHz or a voltage gain of 30 at an IF of 2 MHz.
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All had a normal control grid whose function was to act as a primary control for current passing through the tube, but they differed according to the intended function of the other grid. In order of historical appearance these are: the space-charge grid tube, the bi-grid valve, and the screen-grid tube. The last of these appeared in two distinct variants with different areas of application: the screen-grid valve proper, which was used for medium- frequency, small signal amplification, and the beam tetrode which appeared later, and was used for audio or radio-frequency power amplification. The former was quickly superseded by the rf pentode, while the latter was initially developed as an alternative to the pentode as an audio power amplifying device.
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Unlike today, when almost all radios use a variation of the superheterodyne design, during the 1920s vacuum tube radios used a variety of competing circuits. During the "Golden Age of Radio" (1920 to 1950), families gathered to listen to the home radio in the evening, such as this Zenith console model 12-S-568 from 1938, a 12 tube superheterodyne with pushbutton tuning and 12 inch cone speaker. The Audion (triode) vacuum tube invented by Lee De Forest in 1906 was the first practical amplifying device and revolutionized radio. Vacuum tube transmitters replaced spark transmitters and made possible four new types of modulation: continuous wave (CW) radiotelegraphy, amplitude modulation (AM) around 1915 which could carry audio (sound), frequency modulation (FM) around 1938 which had much improved audio quality, and single sideband (SSB).
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RC oscillators are a type of feedback oscillator; they consist of an amplifying device, a transistor, vacuum tube, or op-amp, with some of its output energy fed back into its input through a network of resistors and capacitors, an RC network, to achieve positive feedback, causing it to generate an oscillating sinusoidal voltage. They are used to produce lower frequencies, mostly audio frequencies, in such applications as audio signal generators and electronic musical instruments. At radio frequencies, another type of feedback oscillator, the LC oscillator is used, but at frequencies below 100 kHz the size of the inductors and capacitors needed for the LC oscillator become cumbersome, and RC oscillators are used instead. Their lack of bulky inductors also makes them easier to integrate into microelectronic devices.
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As long as the gain of the amplifier is high enough that the total gain around the loop is unity or higher, the circuit will generally oscillate. In RC oscillator circuits which use a single inverting amplifying device, such as a transistor, tube, or an op amp with the feedback applied to the inverting input, the amplifier provides 180° of the phase shift, so the RC network must provide the other 180°. Since each capacitor can provide a maximum of 90° of phase shift, RC oscillators require at least two frequency-determining capacitors in the circuit (two poles), and most have three or more, with a comparable number of resistors. This makes tuning the circuit to different frequencies more difficult than in other types such as the LC oscillator, in which the frequency is determined by a single LC circuit so only one element must be varied.
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With artificial aids, Mastermind can cause only one person among many who are present to see his illusions. He is even capable of affecting telepaths as powerful as Professor Xavier and Jean Grey, although to manipulate Dark Phoenix he required an amplifying device called a "mind-tap mechanism" provided by the White Queen that enabled him to project illusions directly into the entity's mind, so that the entity "saw" them, and to monitor the entity's thoughts, both over great distances. Emma Frost described his abilities to the Sentry in the New Avengers storyline as something akin to a psionic virus, which he plants in to the mind of the victim and allows to grow and change according to their view and feelings. It would appear that these "viruses" can continue to function even without his influence, as the illusions placed in to the mind of the Sentry remained after Mastermind's death.
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