This electronic Morse key was found in a Popular Electronics from the 90's. The components are common, but there is a mechanical part that requires assembly skills.
This amplifier with differential input uses two old op amps but can be implemented with modern op amps....
This signal switching circuit uses currently unusual field effect transistors and an operational one that...
This JFET amplifier was found in documentation from 1958. The circuit has voltage gain of 4 and 10...