We found this circuit in a 90s Radio Electronics. The integrated circuit used is uncommon today. The table indicates the components for different operating ranges.
With this name, we found this electronic stethoscope with a coal microphone in a 1957 Raytheon...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
Found in Motorola documentation from the 1970s, this circuit makes use of period components. The lamp is...