Building a power supply is kinda hard

When you find something you want to build from scrap salvaged parts it can be daunting at times. I have been wanting a variable power supply that can go from 1.5v to 24v around 2 or 3 amps. Granted I could toss on a simple LM317 regulator and call it done but I want a couple of options like current limiting, option for negative voltage and so forth. Now I have found great articles, guides and schematics on the one I want to build but a few of the parts I don’t have and tried using a alternative parts in its place. Mostly the OPAmps are a factor. I have tried using some 741 and a couple of general purpose OPAmps that are used for electric music instruments. They work to a degree like only letting me select 1.5v to 4.5volt. I even tried copying mjlorton’s power supply and doesn’t even work. I don’t know if I did something wrong and just can’t see it or I have more bad parts then I thought.

The 741 OpAmp is tricky since it requires a negative voltage but from what I have found on some sample schematics that they just put the negative to ground but when I tried it the damn thing didn’t work so I would toss on a voltage divider and run 6 volts positive and 6 volts negative and I would get only 1.5v to 4.5v and if I tried 12volt positive and 12 volt negative I can only get 3.5v to 11v.

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