In article , Chuck Harris
writes:

When transistor circuits get designed by marginal engineers, they
often end up with stage gains being so close to the transistor's
maximum gain that the transistors need to be selected for proper
operation in the circuit. That ends up being a manufacturer's
nightmare! National's 2N4401's might work 90% of the time, but
Fairchild's only work 10% of the time. This datecode is fine, but
that one is a bust...soon manufacturing is looking for an engineer's
head to put on a pole.

At Bell Labs I heard the story of an early transistorized circuit that was in
mass production for years by Western Electric. Suddenly, one year the new
units started giving trouble. Turns out the designer had assumed a *maximum*
gain per transistor. The transistor plant had finally improved the gain of
that type to where the original circuit would no longer work!

Generally, the more negative feedback you put into a transistor or tube stage,
the less finicky it is about how "hot" a device you plug in. --Mike K.

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