Inter Electrode Or Electron Stream Injection

Grid Controlled Amplification is composed of five types; classified by the location of the bias voltage on the curve formed by the plate current flow plotted against the grid voltage; as follows:

CLASS A—In a class A Amplifier the grid bias is fixed so that plate current flows at all times.

CLASS ABi AND CLASS AB^In a class AB Amplifier the grid bias is fixed so that plate current flows for appreciably more than half but less than the entire duty cycle. The peak driving voltage in a class ABi Amplifier does not exceed the negative bias voltage. In a class AB2 Amplifier the peak driving voltage exceeds the negative bias voltage.

CLASS B~A class B Amplifier has its grid bias at approximately cut off in order that there will be no appreciable current flow when there is not an exciting voltage applied to the grid. CLASS C—A class C Amplifier has its grid bias fixed at a point exceeding cut off so that plate current flows only during a fraction of the input duty cycle.

Class A Amplification finds its greatest use in receiver radio frequency circuits. Class AB and Class B in audio power amplifiers, and Class C in radio frequency power amplifiers.

III. Frequency Mixing: Frequency mixing can be employed in any of the circuits of an electron tube and is converting frequency in superheterodyne receivers, modulating radio frequency amplifiers, and mixing speech and music.

Frequency conversion in superheterodyne receivers is commonly done by pentagrid converter tubes which utilize electron stream injection, ^he input signal (E) is beat against the mixing signal (E2) to give basically the following four signals in the plate circuit: Ei, E2, Ej+E2, and E1-E2; the latter used as the IF signal in the receiver.

IV. Other Circuits: These include automatic gain control, automatic frequency control, bridge, limiter, oscillator, separator, superregenerative, picture tube filter, etc. Since the scope of this manual must be limited these circuits have not been discussed. Careful analysis will show their similarity or that they are a part of the circuits covered in topics I, II, and III.

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