Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.
Although the so-called “boots” or amplifiers that increase the power of transmitters are not...
Another of the many similar configurations we have in this section. This one is from a Radio...
The current of this charger is determined by Rs. The circuit is from the 1982 SGS linear...