> Could I use a hexfet as a pass-transistor so it won't get as hot or is
> this a bad idea for some reason?

In some applications FETs don't get as hot as bipolar transistors would
because they have a very low on resistance (10 - 20 mOhms is readily
available) and therefore have less voltage drop accross them.  FETs don't
just run cooler by some magic.

However, the pass element in a linear power supply will have the same
voltage accross it and current thru it at a particular setting regardless
of how it is implemented.  Voltage x current = power, so whatever pass
element you use will need to dissipate the same power.  That usually
favors bipolar transistors because they tend to be cheaper at the same
power levels.  Also, many FETs are intended for switching use where they
don't dissipate much power, and therefore aren't available in high power
packages compared to their current ratings.


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