Found in a publication by Gernsback from 1960, this circuit uses germanium transistors of the time and commercial coils. It can be changed to operate with modern transistors and other wavebands.
This circuit is from a 1998 Poptronics. The circuit triggers a buzzer after a certain time, waking...
An integrated circuit 741 (operational amplifier is the basis of this voltage indicator, which can also...
This transistorized voltage converter is one of the oldest that we find in technical publications. It...