Figure 9.8 Schematic of Atwater-Kent Model 20. The connection terminals are located on the back of the radio for connection to antenna, batteries, and speaker. There are two connection terminals shown on the left. One is labeled A for antenna and the other G for ground. The G terminal connects to the radio ground. The A terminal connects to the swinger of a 3 position switch. Each of the three stators is connected to a different tap near the bottom of the antenna coil. The bottom of the antenna coil connects to radio ground. There is a single variable capacitor in parallel with the antenna coil. The top of the coil goes to the grid of V1, first RF amplifier. The left side of the filament goes to radio ground. The right side goes to a terminal labeled A plus, B minus. The plate of V1 goes to a link on the interstage coil. The top of this link goes to B plus. The bottom of the interstage coil goes to radio ground. There is a single variable capacitor in parallel with this coil. The top of the coil goes to the grid of V2, second RF amplifier. The left side of the filament goes to radio ground. The right side goes to A plus, B minus. The plate of V2 goes to the bottom end of a link that is wound on the detector coil. The bottom end of this coil goes to radio ground. Radio ground connects to the wiper of the left hand filament rheostat. There is a single variable capacitor connected in parallel with the detector coil. The top of the detector coil goes through a 0.0002 u f, (200 pf), capacitor to the grid of V3, detector. The grid of V3 goes through a resistor to the right side of the filament. The resistor is labeled 2 dash 4 meg ohms. The plate of V3 goes through a capacitor, value unknown, to the right side of the filament. The right side of the filament with the grid leak resistor and plate bypass capacitor goes to A plus, B minus. The left side of the filament goes to the wiper of the right hand filament rheostat. The plate of the detector goes to the low end of the primary of an audio interstage transformer. The upper end goes to plus 20 volts. The low end of the secondary of the transformer goes to A minus. The upper end of the secondary goes to the grid of V4, first audio amplifier. The left side of the filament of V4 goes to the wiper of the right hand rheostat. The right side of the filament goes to A plus, B minus. The plate of V4 goes to the low end of the primary of another audio interstage transformer. The upper end goes to B plus. The low end of the secondary goes to A minus. The upper end goes to the grid of V5, second audio amplifier. The left side of the filament of V5 goes to the wiper of the right hand rheostat. The right side of the filament goes to A plus, B minus. The plate of V5 goes to one of two terminals labeled S P K R for speaker. The other speaker terminal goes to B plus. The A minus terminal goes through the on off switch to the other ends of both rheostats. End verbal description.
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