This power supply protection circuit using a relay was found in a 1967 documentation. The components are from the time, but current equivalents can be used depending on the power source current.
This circuit was obtained from an American 80's documentation. The balanced mixer can be shown in...
Found in a 90s Electronic Design, this circuit generates harmonics from a sinusoidal input signal....
Published in an old Popular Electronics, this circuit makes use of components that are still...