We found this circuit in a 1969 General Electric documentation. The circuit uses transistors of the time and the diodes in the dotted board must be mounted on the output transistor heatsinks.
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...