We found this precision circuit in a manual from the 80's. The operational amplifier is of a common type at the time, and equivalents can be tested. Transistors are general purpose types.
This circuit is a handset receiver that picks up the signal emitted by a coil under the rug or...
The connection of high-value input resistors causes the circuit to behave like a conventional...
This circuit activates a relay when raindrops fall on the sensor. The circuit is from 1960...