This high voltage source, found in 90’s Popular Electronics, can reach tens of thousands of volts. The Q2 transistor must have an excellent heat sink and the 9 V source is high current.
We find this circuit in a 2005 Linear Technology manual. The circuit applies to small DC motors...
This 12V battery charging circuit automatically shuts off at the end of the charge. The disconnect...
This is one of many Morse code audio oscillators that can be found in this section. The circuit...