Thanks to all for the responses.  I'll probably go ahead and
put a couple of silicon diodes of suitable power rating in the circuit
since I would only loose about .3 volts unregulated output.  I imagine
our mains voltage fluctuates more than that from time to time.  That
difference would represent a change in the mains voltage of a whopping
1.5 or so volts.  Since it ends up regulated from about 20 volts down
to 12, it hardly matters.

Martin McCormick
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