Hi Wayne,

Have almost exclusively used the LM-317 and Chinese modules with that chip as long as the minimum voltage doesn't need to go lower than 1.25 .  Good for 1.5 amps self-limiting for heat or use LM-350 for 3 amps.  For more current, use pass transistors.  If using the little Asian modules, add a reverse bias diode from out to in since the modules do not come with one.  I also bolt on a bigger heat sink.  I would have used an LM-317 on this homebrew PS (link below) but I had lots of 5 volt regulators, essentially the same circuit but higher minimum voltage. 
<https://people.ohio.edu/postr/bapix/HBpowerS.htm>

I suppose you could also copy the Astron circuit using the LM-723.  Here's a link where I repaired a dead Astron and added a MOSFET for over-voltage shutoff.
<https://people.ohio.edu/postr/bapix/Astron_VS-35M.htm>

73 de Rich KB8TAD

On Sun, May 15, 2022 at 10:05 AM <releazer@earthlink.net> wrote:
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   
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