This simple low current circuit was found in a Radio Electronics magazine from August 1960. The circuit does not use transistors in regulation, but only zeners directly.
This adapter circuit was found in a 1990 documentation. It is possible to connect a telephone line...
This receiver circuit was found in a Hands On Electronics from the 90s. The circuit uses a PLL...
The operational amplifier of this low current source may be any of the JFET type. The output...