[Hartley118]

Back around 1970 when I was running a university teaching lab, we encouraged students to actually build circuits and measure their performance. When FETs were a bit novel, I introduced a single-stage FET amplifier using a 2N3819. The prototypes had worked fine, but I have a painful memory that out of a class of 40 only around 20 worked as expected: the rest all needed the source bias resistor to be increased from 4k7 to 8k2, requiring some rapid on-the-spot creativity to maintain the all-important confidence of the class. It was interesting that, rather that being randomly distributed, the device characteristics fell into two definite groups of bias requirement.

Martin