This circuit was found in a 1970 US publication. Transistors are still common and the circuit can be used as a PWM shield or pulse transmission modulator.
This fuzz effect for guitars was found in an American 1980s documentation. The transistors may be the BC549...
This circuit was found in a 1963 magazine, but can still be easily assembled with some current...
This circuit came out in an American magazine that no longer exists. It's the Electronic...