variable curent power suply

i need a circuit to make a variable current power supply lets say from 0 to 3 a it doesn't have to start at zero but it needs to be variable as in you use a pot or something else to adjust it i already have and ammeter. so give me a simple circuit that i can solder up or i can maybe make a PCB out of it i have been doing electronics for about half a year or more im good but not really good so if you can explain that would be nice thank you.

Read my post to this thread.

thanks where do you buy your part i get mine from jameco but i don't know if there would be a better site

Good list of suppliers