The circuit shown has a voltage gain of 500 times and can use equivalent FETs like the BF245. The circuit is suggested by National Semiconductor in its 1994 Linear Applications Handbook.
This circuit uses a GE optical coupler. Equivalents can be tried. The circuit is from the GE...
This circuit from a 1995 documentation triggers a set of lamps when the power goes out. In a more...
This circuit uses a JFET at the input to increase the impedance, and is temperature compensated...