Found in a 1966 documentation, this “coin finder” uses components from the era operating at 2.1 MHz. The circuit uses an audio amplifier for detection.
Found in Popular Electronics from the 90s, this circuit generates signals in a frequency range set to...
This circuit provides 6.3V of output from a 9V input. The circuit was found in a Dutch publication from...
Based on operational amplifiers of the time, this circuit from the 1980s has high input impedance. The...