This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
Found in documentation from the 90s, this circuit is based on operational amplifiers of the time....
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....
This traditional oscillator uses two complementary transistors to produce low frequency signals....