WOW~!!
Thanks for the cogent responses.
That was a fair bit of information.
I'm going to spend some time on the Brew Troller site to see if I can make that work for me.
Apparently they have a mode they call PID mode which works sort of like a light dimmer by clipping the voltage with a variable dwll between bursts of power which may work as a PWM - though truly I'd rather reduce the volts not clip them