Carter Duncan Corp.

Joseph K Beller

Bruce Laurence Kennedy

Roger A Modjeski

A variable power amplifier having a constant current differential amplifier driving a cascaded driving amplifier, a variable power amplifier including a vacuum tube for selectively amplifying output signals wherein the drive of the variable power amplifier is determined by the plate shunt resistive loading of the vacuum tube, a push-pull amplifier including an output transformer operatively coupled to the variable power amplifier and to an amplifier output terminal to amplify and apply to the amplifier output terminal a selectively amplified output signal, and a variable damping circuit including a sensing element for sensing the loading on the output tranformer and a circuit for defining a feedback loop for producing a feedback signal having magnitude and polarity which are determined by the sensing element and wherein the variable damping circuit includes a circuit for applying the feedback signal as an input to the constant current differential amplifier to control the current level thereof as a function of the loading on the output transformer as sensed by the sensing element and wherein the plate current resistive loading of the vacuum tube in the variable power amplifier determines the drive thereof to limit the power of the selectively amplified output signals applied to the amplifier output terminal as shown. The combination of a preamplifier having pluggable modules for providing controlled output signals and a variable power amplifier is shown. A method for processing audio frequency electrical signals is also shown.

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Santa Barbara, CA, United States of America

Joseph K Beller