I left this here voor archeologic reasons. Everybody has to learn and makes mistakes. Often you learn a lot from the faults you make. (and I made and still make a lot of them)
I made this around 2008 or so. This should be a FET tester. The principle is not difficult but the one above is not a good one. It worked in the simulation but that must be pure luck. The comparator has an open collector output. And I forgot the pull up resistors. But that was not enough, I made a pcb in Eagle, for the first time. And if you place comparators without “invoking” the PSU pins you end up with a comparator that is not powered. The only advantage of that is the low power consumption….
The strange thing is that it “kinda” worked because I made a “fault” building while adding the missing power-rails and by accident placed the resistors right. Besides that, there is not much need for testing JFETs. Now, 2015, I use a curvetracer or a beautiful Metrix transistor tester for testing semiconductors. (if needed, most times the diode test of a DMM is enough)