This circuit uses the LM2931 which is not a common component today. What it does is to activate a lamp causing it to blink at a frequency determined by the capacitor.
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This variable gain circuit for analog video signals was found in a 90s Linear Technology...
In the figure we show how to connect a power MOSFET to the output of a CMOS function to control a power...
This receiver using a FET appeared in a November 1957 Radio Electronics magazine. It is one of the...