Found in a 73 magazine for radio amateurs of the 1980s, this circuit uses a dual-gate MOSFET. This component is not currently common.
This tone recognizer circuit that relies on R5 and C1 was found in the December 1994 issue of...
This circuit for cars with mechanical breakers (contact breakers) was found in the April 1969...
We found this circuit in the December 1994 Electronics Now magazine. The worthless components are...