13v linear regulated power supply
You can easily make a 13V low current linear regulated power supply with the LM317. The LM317 is a programmable regulator that has the output voltage set via a pair of resistors that form a divider from the output to GND. A simple power supply would consist of these two resistors and two capacitors, one at the input and one at the output. The following picture shows the circuit for an LM317.



For a 13V output you will want an input voltage 16V or more. A typical current value to use for the IADJ is 50uA as can be determined from the part data sheet. For a 13V output you can use the formula in the picture to get the resistor values. If you use precision values of R1=274 ohms and R2=2550 it is possible to achieve an output of almost exactly 13V when the IADJ value is 50uA.