Three stage push-pull amplifier with only one internal coupling capacitor.
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The above circuit illustrates the addition of a gain stage to the previous circuit. A feedback loop returns the output to the input stage's cathode, where the feedback signal is subtracted from the input signal in the conventional negative feedback fashion. The result is that all the tubes are enclosed within the feedback loop and the final distortion and output impedance will be quite low. |
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One point worth highlighting is the 5k resistor that connects the output to the B+. This resistor prevents the top output tube from having to sink the combined current draw from the other output tube, the phase splitter's tube, and the feedback resistor. Because the B+ is a low impedance point in the circuit, this 5k resistor loads the amplifier with its resistance in parallel with the external load impedance. |
Three stage amplifier push-pull amplifier with a different feedback loop that only encompasses the phase splitter and the output stage
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Pg.
21