The rectifiers of continental. These worked until 1988/89, shortly before I began work here (sept 1989) and they had very very very problems, they had a lot of  problems with arcs and instability, as well as unbalances of phase. Here they were as spare with the preheating light bulbs to maintain then warmed up, because I think they needed about 45 minutes preheating  before be ready to work, for that reason the sapre ones were always with these infrared lights, even the first days/weeks after being replaced by solid state rectifiers, until it was seen that the substitution rectifiers went really well. It was a rest for the technicians.