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 circuit from an old Radio Electronics is used to connect headphones to the output of...
This electromyography monitor is from a 1978 publication on operational amplifiers. The components are...
This circuit can switch signals in the 3.5 to 30 MHz band. We found it in a QST magazine from the...