Fail-safe electronic amplifying circuit

Claim 1

An electronic circuit comprising, a first and a second transistor each having an emitter, a collector and a base electrode and interconnected as a differential amplifier, a source of a.c. signals applied to the input of said first transistor of said differential amplifier, said emitter electrodes of said transistors are coupled to a first source of biasing voltage by a common resistor, said collector electrodes of said transistors are coupled to a second source of biasing voltage by a transformer, said base electrodes of said transistors are respectively coupled to said a.c. signals and to negative feedback signals by impedance means, a difference signal derived from the output of said first and said second transistors of said differential amplifier and applied to the input of a power amplifier, a feedback circuit applying d.c. operating potential to said second transistor of said differential amplifier, and the output of said power amplifier supplies said negative feedback signals over said feedback circuit to the input of said second transistor of said differential amplifier and provides an a.c. output signal which is the maximum gain times the difference between said a.c. input signals and said negative feedback signal plus the gain of said power amplifier to a load when and only when each critical circuit or component is functioning properly in a safe manner.