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43-459: Dynatron can refer to: Dynatron oscillator , type of vacuum tube electronic oscillator circuit Dynatron Radio Ltd , British electronics company (1927-55) Dynatron (music producer) , Danish music producer Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Dynatron . If an internal link led you here, you may wish to change

86-424: A bipolar junction transistor , FET , triode, or amplifier of almost any type (non-inverting in this case, although variations of the circuit with an earthed centre-point and feedback from an inverting amplifier or the collector/drain of a transistor are also common), but a junction FET (shown) or triode is often employed as a good degree of amplitude stability (and thus distortion reduction) can be achieved with

129-432: A pentode vacuum tube, in which, instead of the plate, the screen grid has negative resistance due to being coupled to the suppressor grid . See the circuit at right. In the transitron, the screen grid is biased at a positive voltage (battery B1) above the plate voltage while the suppressor grid is biased negatively (battery B2) , at or below the cathode voltage. Therefore, all the electrons will be reflected by

172-431: A bypass capacitor ( C2 ) which has a low impedance at the oscillation frequency, so they have a constant potential difference. The parallel tuned circuit ( C1-L ) is connected between the screen grid and the cathode (through battery B1 ). The negative resistance of the screen grid cancels the positive resistance of the tuned circuit, causing oscillations. As in the dynatron oscillator the control grid can be used to adjust

215-406: A capacitor ( C2 ) so there is a constant potential difference between them, increasing the screen grid voltage will increase the suppressor voltage, resulting in a decrease in screen current. This means the screen grid has negative differential resistance with respect to the cathode, and can be used to create oscillations. In the transitron circuit, the screen and suppressor grids are coupled with

258-412: A current of electrons I G2 away from the plate, which reduces the net plate current I P below the cathode current I C Higher plate voltage causes the primary electrons to hit the plate with more energy, releasing more secondary electrons. Therefore, starting at the voltage at which the primary electrons have enough energy to cause secondary emission, around V P  = 10V, there

301-406: A negative transconductance of only around −250 microsiemens, giving a negative resistance of −4000Ω. Tubes with more grids, such as the pentagrid converter , can be used to make transitron oscillators with higher transconductance, resulting in smaller negative resistance. Hartley oscillator The Hartley oscillator is an electronic oscillator circuit in which the oscillation frequency

344-437: A normal tetrode amplifier this is an unwanted effect, and the screen grid next to the plate is biased at a lower potential than the plate, so these secondary electrons are repelled and return to the plate due to its positive charge. However, if the screen grid is operated at a higher potential than the plate, the secondary electrons will be attracted to it, and return to ground through the screen grid supply. This represents

387-459: A simple grid leak resistor-capacitor combination in series with the gate or grid (see the Scott circuit below) thanks to diode conduction on signal peaks building up enough negative bias to limit amplification. The frequency of oscillation is approximately the resonant frequency of the tank circuit. If the capacitance of the tank capacitor is C and the total inductance of the tapped coil

430-442: A source of instability in amplifiers, the tetrode's main application, tube manufacturers began applying a graphite coating to the plate which virtually eliminated secondary emission. By 1945 the use of the dynatron circuit was declining. In an electron tube, when electrons emitted by the cathode strike the plate , they can knock other electrons out of the surface of the metal, an effect called secondary emission . In

473-411: A tuning fork. If a tuned circuit could have zero electrical resistance , once oscillations were started it would function as an oscillator , producing a continuous sine wave . But because of the inevitable resistance inherent in actual circuits, without an external source of power the energy in the oscillating current is dissipated as heat in the resistance, and any oscillations decay to zero. In

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516-431: Is L then If two uncoupled coils of inductance L 1 and L 2 are used then However, if the two coils are magnetically coupled the total inductance will be greater because of mutual inductance k The actual oscillation frequency will be slightly lower than given above, because of parasitic capacitance in the coil and loading by the transistor. The Hartley oscillator has several advantages: The output

559-506: Is an operating region (grey) in which an increase in plate voltage causes more electrons to leave the plate than the additional electrons arriving at the plate, and therefore a net reduction in plate current. Since in this region an increase in plate voltage causes a decrease in plate current, the AC plate resistance, that is the differential output resistance of the tube, is negative: As with other negative differential resistance devices like

602-469: Is determined by a tuned circuit consisting of capacitors and inductors , that is, an LC oscillator. The circuit was invented in 1915 by American engineer Ralph Hartley . The distinguishing feature of the Hartley oscillator is that the tuned circuit consists of a single capacitor in parallel with two inductors in series (or a single tapped inductor), and the feedback signal needed for oscillation

645-447: Is harmonic-rich if taken from the amplifier and not directly from the LC circuit (unless amplitude-stabilisation circuitry is employed). This may be considered an advantage or a disadvantage. The schematic shows an example with component values. Instead of field-effect transistors , other active components such as bipolar junction transistors or vacuum tubes , capable of producing gain at

688-853: Is taken from the center connection of the two inductors. The Hartley oscillator was invented by Hartley while he was working for the Research Laboratory of the Western Electric Company . Hartley invented and patented the design in 1915 while overseeing Bell System's transatlantic radiotelephone tests; it was awarded patent number 1,356,763 on October 26, 1920. In 1946 Hartley was awarded the Institute of Radio Engineers Medal of Honor "for his early work on oscillating circuits employing triode tubes " and for his work in information theory (which largely paralleled Harry Nyquist ) about "the fundamental relationship between

731-481: Is the dual of the Colpitts oscillator , which uses two capacitors rather than two inductors for its voltage divider . Although there is no requirement for mutual coupling between the two coil segments, the circuit is usually implemented using a tapped coil, with the feedback taken from the tap, as shown here. The optimal tapping point (or ratio of coil inductances) depends on the amplifying device used, which may be

774-455: Is to employ a common-grid (or common-gate or common-base) amplifier stage, which is still non-inverting but provides voltage gain instead of current gain ; the coil tapping is still connected to the cathode (or source or emitter), but this is now the (low impedance) input to the amplifier; the split tank circuit is now dropping the impedance from the relatively high output impedance of the plate (or drain or collector). The Hartley oscillator

817-423: The split-anode magnetron was said to work by "dynatron oscillation". An advantage of the dynatron circuit was that it could oscillate over a very wide frequency range; from a few hertz to 20 MHz. It also had very good frequency stability compared to other LC oscillators of that time, and was even compared to crystal oscillators . The circuit became popular after the advent of cheap tetrode tubes such as

860-424: The transitron oscillator invented by Cleto Brunetti in 1939, are similar negative resistance vacuum tube oscillator circuits which are based on negative transconductance (a fall in current through one grid electrode caused by an increase in voltage on a second grid) in a pentode or other multigrid vacuum tube. These replaced the dynatron circuit and were employed in vacuum tube electronic equipment through

903-419: The tunnel diode , this negative resistance can be used to create an oscillator. A parallel tuned circuit is connected in the plate circuit of the tetrode. The circuit will oscillate if the magnitude of the negative plate resistance is less than the parallel resistance R of the tuned circuit, including any load connected to the oscillator. The frequency of oscillation is close to the resonant frequency of

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946-403: The 1970s. The dynatron and transitron oscillators differ from many oscillator circuits in that they do not use feedback to generate oscillations, but negative resistance . A tuned circuit (resonant circuit), consisting of an inductor and capacitor connected together, is "almost" an oscillator: it can store electric energy in the form of oscillating currents, "ringing" analogously to

989-481: The CRT's deflection coils. However the dynatron had some drawbacks. It was found that the amount of secondary emission current from the plate varied unpredictably from tube to tube, and also within a single tube over its operating life; eventually it would stop oscillating. When replacing the tube, several might have to be tried to find one that would oscillate in a circuit. In addition, since dynatron oscillations were

1032-465: The UY222 and UY224 around 1928. It was used in beat frequency oscillators (BFOs) for code reception and local oscillators in superheterodyne receivers as well as in laboratory signal generators and scientific research. RCA's 1931 prototype television used two UY224 tubes as dynatron oscillators to generate the vertical deflection (28 Hz) and horizontal deflection (2880 Hz) signals for

1075-479: The coils. The original 1915 version used a triode as the amplifying device in common cathode configuration, with three batteries, and separate adjustable coils. The simplified common-drain JFET circuit diagram uses an LC tank (here the single winding is tapped) and a single battery, but is otherwise essentially the same as the patent drawing. The circuit illustrates the Hartley oscillator operation: Variations on

1118-465: The desired frequency, could be used. The common drain amplifier has a high input impedance and a low output impedance. Therefore the amplifier input is connected to the high impedance top of the LC circuit C1, L1, L2 and the amplifier output is connected to the low impedance tap of the LC circuit. The grid leak C2 and R1 sets the operating point automatically through grid leak bias . A smaller value of C2 gives less harmonic distortion , but requires

1161-406: The dynatron and transitron circuits, a vacuum tube is biased so that one of its electrodes has negative differential resistance . This means that when the voltage on the electrode with respect to the cathode is increased, the current through it decreases. A tuned circuit is connected between the electrode and the cathode. The negative resistance of the tube cancels the positive resistance of

1204-416: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Dynatron&oldid=830650842 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Dynatron oscillator Negative transconductance oscillators, such as

1247-471: The negative resistance. Since the transitron oscillator didn't depend on secondary emission it was far more reliable than the dynatron. However, because the screen grid is not designed to handle high power, the oscillator's output power is limited. Other tubes with multiple grids beside the pentode, such as the hexode and pentagrid converter tube, have been be used to make similar negative transconductance oscillators. Pentode tubes used in this circuit have

1290-424: The negative suppressor grid and none will get through to the plate. The reflected electrons will instead be attracted to the screen grid, so the screen current will be high while the plate current will be zero. However, if the suppressor grid voltage is increased, as it approaches zero (the cathode voltage) electrons will begin to pass through it and reach the plate, so the number diverted to the screen grid, and thus

1333-403: The original patent schematic, still results in a working oscillator but now that the two coils are not magnetically coupled the inductance, and so frequency, calculation has to be modified (see below), and the explanation of the voltage increase mechanism is more complicated than the autotransformer scenario. A quite different implementation using a tapped coil in an LC tank feedback arrangement

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1376-410: The plate is given a coating which drastically reduces the unwanted secondary emission, so these tubes have virtually no negative resistance "kink" in their plate current characteristic, and cannot be used in dynatron oscillators. The tetrode wasn't the only tube which could generate dynatron oscillations. Early triodes also had secondary emission and thus negative resistance, and before the tetrode

1419-430: The plate when electrons from the cathode hit it, called secondary emission . This causes a downward "kink" in the plate current vs. plate voltage curve (graph below, grey region) when the screen grid is biased at a higher voltage than the plate, as described below. This negative resistance was mostly a feature of older tubes, of 1940s or earlier vintage. In most modern tetrodes, to prevent parasitic oscillations

1462-427: The positive resistance, the voltage swing will extend into the nonlinear part of the curve, and the peaks of the sine wave output will be flattened ("clipped"). The transitron oscillator, invented by Cledo Brunetti in 1939, (although a similar effect was observed in tetrodes by Balthasar van der Pol in 1926, and Edward Herold described a similar oscillator in 1935 ) is a negative resistance oscillator circuit using

1505-453: The screen current, will decrease. Since the other grids don't take significant current the cathode current I C {\displaystyle \scriptstyle I_{\text{C}}} is split between the plate I P {\displaystyle \scriptstyle I_{\text{P}}} and the screen grid I G2 {\displaystyle \scriptstyle I_{\text{G2}}} : The division of current between

1548-447: The screen grid and plate is controlled by the suppressor voltage. This inverse relationship is indicated by saying the transconductance between the screen and suppressor grid (the change in screen current Δ I G2 divided by the change in suppressor voltage Δ V G3 ) is negative. Since the suppressor grid voltage and not the screen grid voltage controls the screen current, if the suppressor and screen grid are coupled together with

1591-410: The simple circuit often include ways to automatically reduce the amplifier gain to maintain a constant output voltage at a level below overload; the simple circuit above will limit the output voltage due to the gate conducting on positive peaks, effectively damping oscillations but not before significant distortion ( spurious harmonics ) may result. Changing the tapped coil to two separate coils, as in

1634-438: The total amount of information which may be transmitted over a transmission system of limited band-width and the time required." The Hartley oscillator is distinguished by a tank circuit consisting of two series-connected coils (or, often, a tapped coil) in parallel with a capacitor, with an amplifier between the relatively high impedance across the entire LC tank and the relatively low voltage/high current point between

1677-496: The tuned circuit they could operate over a wide frequency range, from a few hertz to around 20 MHz. Another advantage was that they used a simple single LC tuned circuit without the taps or "tickler" coils required by oscillators such as the Hartley or Armstrong circuits. In the dynatron a tetrode tube is used. In some tetrodes the plate (anode) has negative differential resistance, due to electrons knocked out of

1720-449: The tuned circuit, creating in effect a tuned circuit with zero AC resistance. A spontaneous continuous sinusoidal oscillating voltage at the resonant frequency of the tuned circuit is generated, started by electrical noise in the circuit when it is turned on. An advantage of these oscillators was that the negative resistance effect was largely independent of frequency, so by using suitable values of inductance and capacitance in

1763-469: The tuned circuit. As can be seen from the graphs, for dynatron operation the screen grid had to be biased at a considerably higher voltage than the plate; at least twice the plate voltage. The plate voltage swing is limited to the negative resistance region of the curve, the downward "kink", so to achieve the largest output voltage swing, the tube should be biased in the center of the negative resistance region. The negative resistance of older tetrode tubes

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1806-422: Was around 10kΩ - 20kΩ, and can be controlled by varying the control grid bias. If the magnitude of the negative resistance | r P | is just small enough to start oscillation, just a little smaller than the positive resistance R of the tuned circuit, the oscillation frequency will be very stable, and the output waveform will be almost sinusoidal. If the negative resistance is made significantly smaller than

1849-552: Was invented they were used in dynatron oscillators by biasing the control grid more positive than the plate. Hull's first dynatron oscillator in 1918 used a special "dynatron" vacuum tube of his own design (shown above) , a triode in which the grid was a heavy plate perforated with holes which was robust enough to carry high currents. This tube saw little use as standard triode and tetrodes could function adequately as dynatrons. The term "dynatron" came to be applied to all negative resistance oscillations in vacuum tubes; for example

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