The Audio-frequency Power Amplifier

Introduction to Audio Power Amplifier

In this tutorial we shall study vacuum-tube amplifier circuits which give a large output voltage of substantially the same waveform as that of the input voltage, accompanied by a large curr ent of like waveform, so that there is considerable power delivered to the load, rfhe operation really is a power-conversion process, as in most cases all of the output power derives from the plate d-c source, under the control of the signal voltage applied to the grid. In general the treatment can often be made similar to that used for voltage amplifiers, except that usually the operation is not linear and therefore graphical or experimental procedures give most accurate results.

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Feedback Amplifiers

Distortion and Stability in output

It is well known that the output of an amplifier does not have a voltage waveform exactly a replica of the input signal. Because of the presence of inductance and capacitance in the tubes and circuits, the various frequency components of the signal are affected by different amplifications and phase shifts. Also because of nonlinear action of the tube itself, the output voltage is not exactly prop optional to the input voltage. Again, if one or more of the bias voltages E0, Eb0, etc., varies,

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Meachom Bridge Oscillator

Meachom Bridge Oscillator with circuit

The Meacham bridge oscillator, illustrated in figure 1460, provides the greatest frequency stability of any vacuum-tube oscillator yet devised, but the region of maximum frequency stability is limited to the lower frequencies because of the increased effect of the 8cray circuit capacitances when the frequency becomes greater than a few hundred kilocycles per second. The oscillator is of the crystal-stabilized type employing tuned circuits. At frequencies above 1000 kv the effect of the stray capacitance is sufficient to reduce the stability to a point where little is to be gained by the use of the Meacham

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Crystal Oscillators

Oscillators with Crystals Having Two Sets of Electrodes

The original crystal oscillator devised by Dr. Nicolson, as well as a number of the earlier crystal oscillators tested by Dr. Cady, employed crystals with, effectively, two pairs of electrodes. The basic circuit is shown in figure 1-156. The re quired phase inversion of, the amplifier output voltage is provided by the crystal unit operating at a mode for which the polarities of the plate and grid terminals with respect to ground are 180 degrees out of phase. The circuit shown operates the crystal unit very

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Miller Oscillator with Cricuit

1428. The Miller oscillator is the crystal equivalent of a Hartley oscillator in which no mutual inductance exists between the plate-to cathode and gridt o.cithode inductances. ( See figure 1-140.) The Miller oscillator has an average frequency deviation of approximately 1.5 times that of the Pierce circuit. The plate circuit must appear inductive in order that the correct phase shift will be produced in E, the plate r-f voltage, to compensate for the

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Principles of Rectification

BasicPrinciple of Rectification

Rectifiers change ac into pulsating dc by eliminating the nega Live half’cycles or alternating the ac voltage. Only a series of sinewave pulsations of positive polarity remain. An ideal rectifier may be thought of as a switch that closes a load circuit whenever the polarity of the alternating voltage is positive, and opens the circuit whenever the alternating voltage is of negative polarity. A switch

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