This circuit was found in a British documentation from 1969. It can be implemented with modern transistors. The pass band is 6 MHz.
This circuit was found in a 1980s documentation. Modern general purpose transistors can be used....
Found in a 90’s Popular Electronics, this circuit uses a component that can be difficult to obtain...
Suggested by Fairchild in a 1980s publication, this multiplier uses operational amplifiers from that...