Peter, I'm not sure how to make a carbon pile regulator, but I imagine there must be something on the net. It's old technology after all. Just a couple of other thoughts.. 1)rotary stud switch with home made BSRs (big sweaty resistors), perhaps from a scrap electric fire. I haven't done any sums on this, I suspect you'd need several in parallel to take the current. 2)I looked at some fork lift truck control circuits many years ago. In those days the only high current device available was a thyristor, which was fine for turning on but needed something a bit clever for switching off. From memory, one thyristor was turned on, and to turn it off, another thyristor in parallel shorted it out (the only way to turn them off was to remove the supply or let the current drop to zero). The cunning thing was that this second thyristor had a capacitor in series, which charged up to the supply voltage. At this point the current in the second thyristor fell to zero, so it too turned off. I seem to remember the capacitor was referred to as a commutating capacitor. One obvious question is how the second thyristor turns off the first - I guess something is arranged to ensure that the volts drop across the second is less than the first. You've whetted my appetite so I'll have a rummage on the web and see what I can find. JohnP MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.