This circuit was obtained in a 1964 Electronic Design. Equivalent modern transistors can be used. The circuit requires a 6 V symmetrical power supply.
This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high...
This is one of the many versions of this type of indicator that the reader can find on our...
Found in an English publication from the 1980s, this circuit can be built with equivalent...