This is the basic configuration of an operational amplifier sample & hold circuit. The FET and transistor are commonly used. The circuit is from an 80's documentation.
From a 90s Popular Electronics, this circuit emits pulsating signals for different types of...
Found in a Popular Electronics from the 90's, this circuit converts a 40 V symmetrical source to a 5...
This circuit generates frequencies determined by R3 and C1. We found it in the Radio Electronics magazine...