Philp Lalone asked about applying the uA723 VR.

The uA723 has been around forever, but it's a very versatile device: I guess
that's one reason it's still around after all this time!  (I've used them on
and off in my designs for about 20 years).  It is available in a Dual in
line package, as well as a tall TO-5 style metal can.

What may be a little confusing (as compared to common-garden 3 terminal
devices) is that there are several distinct application topologies, relating
to differnet modes of operation.  With a little ingenuity, you can configure
its functional blocks to provide the following functions:

  - outputs above Vref (7.15v),
  - outputs below Vref,
  - fixed or adjustable output
  - low output currents, with only its internal pass device,
  - with an external pass device for high output currents,
  - series or shunt regulator configs,
  - in a free-running switched-mode configuration
  - in a driven switched-mode (PWM) configuration
  - as a current source
  - and likely many other things I haven't thought of yet

The best sources of info are the Linear Applications books from Mot or
NAtional.  Just be careful, especially in the switched-mode configurations:
the uA723's op amp is a (comparativley) wide-bandwidth device, making layout
and grounding critical to a  successful design... you may end up with an
oscillator instead of a regulator!

However: unless you need the flexibility or high performance, *and* can pull
off the design, why not just use a good ol' 3-terminal device?  It can be
very easy to botch a uA 723 design if you're not experienced with analog design.

Hope this helps,
....Gregg