This simple step of low power audio is from a 1975 documentation. The transistor can be a BC548, and the transformer of the type found in small transistor radios and recorders of the time.
This circuit is from a 1992 publication. The transistors can be the BC549 or BC548 and the power...
This receiver for frequencies up to 18 MHz was found in American documentation from the 1990s. Data...
This toy musical instrument has the notes given by the capacitors on the keyboard. The circuit can be...