Eh, took me a bit longer than “a bit”. (eye roll)
I did just post #27, paragraph 4 applies in particular. :-)
Indeed, there are cheaper linear regulated supplies on Amazon, eBay, etc., that with good heat sinking of the regulator chip and output transistor could easily crank out a couple amps, especially given that the voltage drop when limiting the output will be modest. BUT... same problem — if the input is 13 volts, what does the output do?
It occurs to me that SOMEWHERE around here I should still have my old audio op amp prototyping breadboard which had either a 7815 and a 7915 in the power supply section, or possibly a 7818 and a 7918, as I sometimes worked with +/- 18v supply rails and NE5532’s and NE5534’s. I could muck around with the 7815, for example, to see how the output behaves as the input decreases. If below a supply voltage of 18 volts or so, the output pretty much follows the input, no problem. I don’t really need true regulation, just voltage limiting. But if the regulator turns off when the input falls under 17v or so, that’s no good.
Then I would go on the assumption a 7812 would behave much the same, just at 3 volts less all around.
I still think the zener-transistor circuit MAY do what I want, so, I have parts ordered and will see what happens... If it doesn’t work I’m out ~$15 and will have several extra 13v zeners and TIP31C’s to add to the parts bins. Plus I got up to $35 for my Amazon order, finally! :-)