This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent components. The transistors may be BC558 and the transformer is obtained from a disused transistor radio.
We found this circuit in a 2002 documentation. The frequency of each note is determined by the...
This circuit memorizes the input voltage that is then applied to the load in the form of a...
This interesting circuit found in American documentation generates a busy signal, without you...