This circuit is from a 1968 documentation. It makes use of thermistors (NTC) to indicate overheating of charged batteries. Modern equivalent components can be used.
This encrypted key was found in a 1989 documentation. It controls a relay that is activated only...
This circuit is from an American transistor book from the 60's. The transistor is germanium of the...
This simple SCR alarm circuit was found in an old Poptronics, but can be easily assembled as all...