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.
This is the circuit of an old oscilloscope, using components from the 80s. Of course, it serves...
This circuit controls a heating element using a triac. Triac must be fitted with a heat sink. We...
This complex circuit with many digital components measures inductances in 6 ranges ranging from 100...