The operational amplifier used is not common today, but the circuit can be implemented with modern operational ones. The gain is 1000 and the source must be symmetrical.
This circuito from the 1977 GE Semiconductor Manual circuit provides timings from 0 to 90 seconds...
Suggested by General Electric in a 1965 document, this circuit can accept a greater number of...
This circuit with an unusual configuration was found in the January 1974 issue of Radio...