This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which in many cases were arrays of transistors allowing use as audio amplifiers, as in this case.
This circuit with the 555, was obtained in a 90s American documentation. The signal must be...
In the figure we have a simple and efficient way to obtain rectangular signals from an astounding 555...
This is the traditional Hartley Oscillator configuration for high frequencies. For 1 MHz wind 80...