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October |
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Page 4 |
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Copyright © 2003 John Broskie All Rights Reserved |
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Generic one-tube-on-top-of-the-other push-pull class-AB amplifier |
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In the circuit to the right, we see the classic totem pole configuration. Both triodes, top and bottom, can simultaneously function as grounded-cathode amplifiers or as cathode followers, depending on the driver stage’s configuration in relation to the output stage. In this example, we witness a cathode follower functioning from both output tubes, hence the larger input signal swing for the top triode than for the bottom, as the top triode’s cathode must follow in phase the output signal and while the bottom triode’s cathode is effectively grounded through the large power supply capacitor to ground, the driver stage will return output to the bottom triode’s grid, so that it too will function as a cathode follower. (Whenever you are evaluating a circuit’s AC operation, imagine that the power supplies and capacitors have been shorted out with wires, as they effectively are dead shorts to AC signals, at least to high-frequency ones.) |