From Crystal Sets To 405 Line television


Posted on Feb 7, 2014

A valve radio receiver in its crudest form is a frequency determining tuned circuit, (consisting of an inductor and capacitor in parallel) followed by a series of valves coupled together. These valves act on the signal and provide high frequency amplification, detection (rectification) and low frequency amplification (audio amplification). A louds


From Crystal Sets To 405 Line television
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peaker or headphones terminates the line of valves. There are several ways in which linkage can be provided between the separate valves; the basic methods will now be shown. This arrangement is shown in Figure 3a. There is a resistor (Ra) between Valve A`s anode and the H. T supply. The A. C signal on the anode of valve A is passed to valve B via capacitor C, which should be well able to withstand the H. T supply voltage. In the event of a breakdown of this component, the grid of Valve B would be exposed to damaging H. T voltage from Valve A`s anode. Resistor Rb is to provide a path for electrons from the grid of valve B (the so-called grid leak resistor). The capacitance value of C is chosen to present low impedance to the signal to be processed. Resistance - Capacitance coupling is only suitable for use at audio frequencies (20Hz-20 KHz); above these frequencies capacitive effects in the valve reduces the gain possible from the coupled stages. This arrangement follows the form of the capacitive-resistive coupling illustrated in diagram 3a but the resistor between the first valve`s anode and the H. T voltage is replaced by an inductor (choke). The inductor and Capacitor values will depend on the frequency that the stage is required to operate at and the impedance of Valve B`s input circuit. This is arrangement is shown in figure 3b. It requires the use of a transformer (TR1) that is able to withstand the anode current from...




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