This circuit reproduces the dial noise in a small speaker. The transistor can be a general-purpose type. We found it in an 80's Electronic Design.
The figure shows how to use CMOS inverters as amplifiers. The circuit is from a Radio Electronics from...
This interesting circuit measures the distortion of the sinusoidal voltage of the power grid. We...
This circuit was found in an American publication from the 50's. The transistors are made of...