I have used an ancient Raytheon voltage regulator for many years. A more comon brand is Sola. These simple regulators rely on perhaps something like a magnetic amplifier instead of more delicate electronic devices. Standard 120 volt incandescent enlarger bulbs last a long, long time.
Decades ago, when I operated 16mm movie projectors, we wired a 12 volt filiment transformer as a step-down transformer. This greatly extended projector lamp life.
As a matter of fact, my enlarger now has both a rewired filament transfomer and a dimmer switch. That keeps me from accidentally zeroing the dimmer.