Single-Stage Degenerative Amplifier

Author: J.B. Hoag

Fig. 26 B. A simple degenerative amplifier

In Fig 26 B, the negative feedback voltage is transmitted through the condenser C₁ and resistor R₁ and appears across resistor R₂. Suppose, for instance, that an input signal makes the grid of the tube less negative for a moment. The resultant increase of plate current produces a negative potential at the top of the primary of the output transformer. This is transmitted through R₁C₁ to R₂. The top of R₂ becomes negative for a moment, and, through the secondary of the input transformer, makes the grid negative, the reverse of the positive impulse of the input signal.

Fig. 26 C. Another simple degenerative amplifier

In Fig. 26 C, the cathode resistor R₂ is used simultaneously to provide the C-bias and for the feedback purpose. When a positive impulse occurs on the grid, the plate current increases; and also the ir drop in R₂ increases because it is in the plate circuit. An increase of voltage across R₂ makes the grid more negative, the reverse of that of the signal voltage.