An Output-Transformerless Amplifier
An amplifier with no output transformer is described. The output stage is single ended, and the tubes are connected in series. The cathode-coupled phase-inverter drive is used to drive the output stage. An analysis of the driver circuit is followed by a description of the amplifier and its performance. With 20 db of negative feedback, frequency response is flat to 30 kc, down only 1.5 db at 100 kc. A power output of 3 watts is obtained into a 600-ohm load with an input signal of 0.8 volt. Intermodulation distortion is only 0.7% at 3 watts.
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