This 800 Hz sinusoidal oscillator was found in a 1970s American documentation. The transistor supports a modern general-purpose equivalent. The frequency is given by the RC network that can be changed.
Common operational amplifiers can be used on this circuit. The resistor with no value in series with...
Carefully removing (and a lot of work) the cover of a metallic 2N3055 to expose its joints it...
The circuit shown, found in French documentation from the 1970s, functions as a variable...