The Ebers-Moll Effect Transistor Used as a Low-Value Controlled Resistor in ACC and Other Variable-Gain Applications

An Automatic Chroma Control (ACC) amplifier was developed using for gain control a conventional small signal transistor operating as a variable degeneration element in the emitter of the amplifier stage. The gain-control transistor was operating around the knee of its collector characteristic, and acted like a linear variable resistor. The resistance was controlled by a small DC current in the base. Mathematically, the behavior of such transistor was described by Ebers and Moll in 1954 -hence the name.