Yep. Seen those types of units and was about to mention them. One
model had a core that had a space in it much like a D'Arsonval meter
movement. The space was filled with a 'bobbin' that when cross-ways left
two large air-gaps and when aligned would neatly bring the gap between
the two sides of the core. A weight and lever would turn the 'bobbin'
into/outof the core to control the current.

Problem with those is, if you get a loose connection or arc, the unit
will just keep pumping power to the system no matter what.

daestrom



The only place I've seen those used was for regulating current in 6.6A
(usually) series loop streetlighting. Lots of this still left in the Los
Angeles area and a few other pockets but most is gone by now. It was
very common from the 20s up through the 60s though, incandescent at
first, but 6.6A matching transformer "ballasts" are available for HID
lamps as well. Most airfield illumination is still 6.6A series, I
suspect the modern control gear is solid state.

Westinghouse had a design where the secondary was on a linear mechanism
with a counterweight and would float above the primary. Current was
adjusted by moving the counterweight.