Re: -5V
If you have a power supply with a negative voltage output you can tap off the transformer, filter, and use a regulator. The regulator can just be a series transistor with a feedback transistor. Make sure the gain is right and use the collector of the feedback resistor to control the voltage at the base of the series transistor. Be sure the current of the series transistor always remains constant, so add a load if you have to. The VCE will have a wide range because it's normally a high current transistor.