Servicing Radio And Sound Equipment


Posted on Feb 5, 2014

The tuned circuits of capacity and inductance used in vacuum tube transmitter circuits are frequently called `tank` circuits, because from one viewpoint they act as tanks or reservoirs of RF energy. Blocking Capacitors. -Blocking capacitors are used to provide a high impedance path for DC or low-frequency AC, and so prevent the flow of such currents


Servicing Radio And Sound Equipment
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without appreciably affecting the flow of RF. Series and Parallel Feed. -The DC grid and plate voltages required for tube operation may be fed through the coil of the tuned circuit, or may be fed through a choke in parallel with the tuned circuit. In the first case the voltage feed is called series feed, in the second, it is called parallel feed. The connections are shown in Figure 59. Filament Center-Tap. -When filament type tubes are heated by AC, the grid and plate returns must be made to the electrical center, or center-tap, of the filament circuit in order to avoid hum. Excitation. -In transmitters, the AC signal voltage applied to the grid of a tube is called the excitation, or the exciting or driving voltage. Exciting or driving power is the power required to develop the exciting voltage across the grid circuit. Oscillators supply their own excitation, but amplifiers must be driven by voltage from an oscillator or from another amplifier. Power Input. -Unless otherwise specified, the term power input applies to the DC power consumed in the plate circuit. It is the product of the DC plate voltage and current. Power Output. -It is important to distinguish between the tube power output and the circuit power output. The tube output does not take into account the tank and coupling circuit losses. Antenna Feeding. -Distances along an antenna are usually expressed in terms of electrical wave length. Every half wave length...




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