This conventional filter circuit is from American documentation from the 1990s. The operational amplifier admits an equivalent and the power supply must be symmetrical.
This transistorized “grid dip” oscillator was found at Radio Electronics in June 1953. The...
This circuit has a very traditional configuration that can be found elsewhere on the site. R2 and...
This high input impedance amplifier stage was found in a 1963 documentation. The transistor...