For analog lines, this circuit was found in the August 1994 issue of Electronics Now magazine. The transistors are common general-purpose types.
We found this ultrasonic emitter in a 1964 publication. The transducer is a piezoelectric type....
This 80's circuit has an input resistance of the order of 880 M and gain 10, using operational...
This circuit was found in 1968 General Electric documentation. The circuit uses components from the era...