With this circuit it is possible to tune an AM signal using a 5k potentiometer (4k7). The circuit was found in a publication from the 1980s and the PLL can be replaced by an equivalent one, with tests.
This circuit is from an old publication from 1977 and can be implemented with more modern...
This basic buffer circuit can be implemented with other operational amplifiers. The circuit is...
This circuit can be applied to other 3-terminal regulators and equivalent transistors can be used....