The usual advantages of transistorized amplifiers—lowered power consumption, lighter weight, improved compactness, and increased reliability—are often cited. A fifth consideration is improved performance.

One of the elements previously limiting amplifier performance is the AGC losser device. A photo-resistive device can approach five idealized requirements quite closely. The amplifier described uses four cells of photo-resistive material mounted in a common configuration. The four cells are illuminated from a common miniature lamp. Voltage for the lamp is derived from AGC control circuits. Resistance of the cells, and hence loss across them, depends on the level of illumination.

Temperature compensation is achieved for the entire amplifier by use of a “fifth” stage with current derived from it being fed back to the other four primary amplifying stages.

Amplifier performance and stability are illustrated by graphs of pertinent data.

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