Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
This circuit is from an Italian magazine Radio Elettronica of January 1977. The circuit shows how...
This is one of the possible timer configurations with the 555. We found it in October 1986 Radio...
This circuit was found in a 1969 US documentation. It provides a signal that can be externally...