This Small 5-volts DC Regulator. without IC-7805. Using transistors are interesting. If you have an old transistor or want to save. It may be a good choice.
This is 5v 12v dual power supply circuit using 2N3055 and Zener diode for 12V then to LM309 or IC-7805 dc regulator IC for 5V output which easy circuit [...]
Although it is ancient, it is still interesting.
Though very ancient, it still is many useful.
This is inverter circuit, 12VDC to 220V 50Hz at 500W power.It easy to make and Low cost. using basic parts transistors 2N3055,IC-4047,