Чтение общенаучной литературы. Кытманова О.А. - 8 стр.

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9
the centre tap, diode D, conducts current I, in the direction indicated by an arrow.
During the next half-wave the voltage polarity will be reversed and Diode D2 will
conduct current I2 to the common load. During both half-waves the current
through the load resistor R (It and I2) is of the same direction, the output current I
= Ij + Ia being of a pulsating wave-form.
Vacuum-Tube Oscillator
То broadcast the human voice by radio, a generator of alternating current of
extremely high frequency and constant amplitude is required. In commercial
broadcasting stations and amateur transmitters this function is performed by a
vacuum tube and circuit of relatively simple design.
One type of oscillator circuit is shown in Fig. 13. When the switch S is closed
connecting the B-battery to the plate of the tube an electron current from the
cathode К to the plate P
starts a current in the circuit
PRVL3K. This growing
current in L3 creates an
expanding magnetic field,
which cutting across L2
induces a current in the grid
circuit in such a direction that the grid becomes negative. A negative charge on the
grid causes the plate current to decrease. This decreasing current causes the field
about L3 to collapse, thus inducing a reversed current in the grid circuit and
therefore a positive charge on the grid. Such a charge increases the plate current
and the above process is repeated.
If the two circuits L2C2 and PRVL3 were properly tuned by adjusting C2
resonance would occur and energy from the B-battery would be continuously
supplied to keep the oscillations going with constant amplitude. The graph of the
continuous oscillations
shown in Fig. 14 represents
the voltage across L3 as it
varies in time. The L3C2
circuit controls the
frequency by controlling
the grid potential while the
large voltage and current
fluctuations take place in the L3 circuit.
The oscillatory circuit. An inductance and capacitance, connected as shown in
simplest, schematic form in Fig. 15 form the necessary elements of all oscillating
circuits. If initially the capacitance is charged as indicated, the surplus electrons on
the plate below cause a surge of negative charge counterclockwise around the
circuit to neutralize the positives and, in so doing, set up a magnetic field in and
around the inductance. When the positives become neutralized and the electron
current tends to cease, the magnetic flux linking the circuit decreases and keeps the

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