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Home Electronic Applications in Communication Amplifiers Resistance-Coupled Audio- Frequency Voltage Amplifiers | |||
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Resistance-Coupled Audio-Frequency Voltage AmplifiersOne tube and its associated circuit often give insufficient voltage gain, and hence two or more tubes are connected in tandem, or cascade, to provide additional amplification. A circuit arrangement is shown in Fig. 19. Capacitor Ci is to prevent the flow of direct current from the source through the grid resistor Rg. The electrons returning from the plate through resistor Rk to the cathode cause drops in voltage across cathode resistors Rk and self-bias the tubes the desired amount. Resistors Rg impress these bias voltages on the control grids of the tubes. Cathode capacitors Ck prevent appreciable alternating signal voltage from being produced across Rk by the plate-current signal variations. This prevents feedback (page 300). The load resistors RL are discussed on page
285. Capacitor Cc is the coupling capacitor that isolates the plate of one tube from the grid of the next, so that these electrodes can be at different direct potentials. Capacitor C0 is to prevent the flow of direct current into a device connected to the output terminals. Capacitor Cf and resistors Rf are decoupling capacitors and decoupling resistors. They provide filtering to prevent the flow of alternating signal components from the tubes back into the power supply which is common to both tubes. This prevents motor-boating, which is a type of low-frequency oscillation.
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Home Electronic Applications in Communication Amplifiers Resistance-Coupled Audio- Frequency Voltage Amplifiers |