[ARC5] Anybody Know Good Regulator Circuit?

[releazer at earthlink.net]

Some years ago I bought a Tema 0-20VDC power supply on ebay.  The seller reported that it seemed to have been modified to produce a steady 25 VDC output by a change to a trimpot.  I finally got around to replacing that "bad" trimpot but that had no effect.  I then realized that the 25 VDC output is simply the unregulated output of the rectifier.  Obviously the regulator section had failed, so I replaced the HA17324 op amp, the only active component in the regulator board, but that did not fix it.
 
Lacking any schematics or other troubleshooting info, I think the simplest thing is to simply build a new regulator section using a suitable circuit; it simply feeds the bases of a bank of power transistors.  Any of y'all have a favorite IC for that application?
 
Thanks!

Wayne
WB5WSV