Direct Coupled Detector and Amplifiers with Automatic Grid Bias

A system for direct coupling of vacuum tubes to give composite detection and amplification is described. The system is designed to avoid frequency discrimination in amplifying audio frequency, and to be free from electrical and acoustical feed-back effects. High-μ tubes are used to control the output of the power amplifier through the aid of the very high filament-to-plate impedance of such tubes with extremely small expenditure of energy therein, and in such a way as to avoid effect of so-called "detector overloading." Microphonic effects are avoided. A unique method of automatically regulating the system to be responsive to carrier currents of different intensities is described, and includes an extension of the automatic effect to volume control. The entire system is designed to be inexpensive and extremely simple in the matter of construction.