Howdy Dave......I like your simple solution to use a 7915 from your junk
box and in the process, simplifying your circuitry a little! Of course
my first choice would have been something like a 7912 with a single gen
purpose diode (1N4001 etc) inserted in the leg to ground to bump the reg
voltage output up nearer to 13. With your 7915 you could likewise add a
couple of similar diodes in series with the output to lower the voltage
to your load.

Keep on tinkering.


Gord