Found in a 1964 Electronic Design this circuit compares two signals by providing the inverse of the algebraic sum of their frequencies. The circuit can be made with modern equivalent transistors.
This simple circuit of a question-answer minicomputer with tray was found in a 1987 magazine. The...
This receiver for listening on the phone was found in a Japanese magazine in 1967. The circuit uses...
We found this circuit in a 1977 publication for radio amateurs. It serves to test general purpose...