Two-Stage Degenerative Amplifier

Author: J.B. Hoag

Fig. 26 D. A typical two-stage degenerative amplifier

Figure 26 D shows a typical two-stage degenerative amplifier. When a positive impulse is applied to the grid of the first tube, the grid of the second tube goes more negative, due to the usual phase reversal of a single-stage amplifier. When, as a result, the plate current of the second tube decreases, the top of the output resistor becomes more positive. This is transmitted through C₁R₁ to the top of R₂, hence making its grounded end more negative. This is applied via the grounds through the input grid resistor to the grid of the first tube, and in opposite phase to that of the impressed signal.

With two stages, the feedback factor FA can be made larger than with one stage, making possible to a fuller extent the potential advantages of this type of amplifier.

Fig. 26 E. A three-stage feedback amplifier

A three-stage unit is shown in Fig. 26 E. This operates, in the absence of R₃C₃, as a degenerative amplifier.