This simple tone control using two transistors was found in an Electronics Today International of the 90s. Transistors are general purpose NPN types, like the BC549 for greater gain.
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...
Found in Popular Electronics, this sophisticated short-wave receiver requires a lot of skill from...
This circuit is from an old American documentation using LEDs in the rectification. The circuit...