This circuit was found in an American documentation from the 70s. The operational amplifier is from that time. Modern equivalents can be used.
This telegraphy circuit generates an audio tone from a pure RF carrier. We found it in a...
The idea of this circuit is a resistance meter or continuity test with a common microammeter or...
This low-pass filter with 741 op and symmetrical source was found in the August 1993 issue of...