The publication provides information on the parameters of single-transistor cascades (on bipolar and field-effect transistors). Main parameters of amplifiers are considered. Elements of feedback theory and its influence on device parameters are described. Information is given on the construction of scaling amplifiers (inverting, non-inverting, differential) using an operational amplifier, as well as information on basic functional circuits based on op-amps: analog adders, integrators, differentiators, converters and analog multipliers.