The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
Found in a 90’s Popular Electronics, this circuit generates sinusoidal signals with frequency...
An interesting basic circuit for projects is the one shown in the figure which consists of a...
This power supply with a power inverter was found in a documentation on transistors from 1960. The...