This circuit was found in a 1966 EEE. What it does is it converts the logic levels of 0 V and +4 V into -6 V and +6 V. Some older type transistors can be replaced by modern equivalents.
This interesting capacitive water level sensor was found in Popular Electronics. The circuit can be...
LTC7841 PolyPhase® Synchronized Boost Controllers Mouser Announces Analog Devices LTC7841...
This circuit was fond in an old publication of the years 1950. The transistors are germanium types and...