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.
This 1 kHz oscillator uses a Norton LM3900 operating system. The frequency depends on C1 and R1...
This configuration was found in a 1990s documentation. Modern operational amplifiers can be used...
This voltage regulator from STMicroelectronics provides a 1,2 A current in the voltage range from...