This detector uses an unusual sensor today. The circuit is from an 80s documentation. Its sensitivity is 10 ppm. The transformer has two secondary voltages.
This 1kHz rejector filter can be modified to operate at other frequencies. Operational can be just...
This small audio amplifier is based on the LM390 with a minimum of external components. We found it...
We found this circuit in the Audio Handbook of the National Semiconductor of 1977. The circuit is used...