This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is 1000 M ohm.
Found in a Popular Electronics from the 80's, this circuit triggers an SCR keeping an LED on when...
This circuit was found in a 1994 documentation. Speed measurement pulses are obtained by a reed...
I found this Vox circuit or acoustic receiver as it was originally called, in a 1973 publication. The...