[Oldcodger]

An idea I've only seen applied to KV regulation ( as used on submarine cable PSU) is to use saturation of the core via a second winding to keep the transformer output volts stabilised. The two systems I have in mind fed circa 500mA at a few KV regulated on cables carrying approx five 12 channel groups at 3khz spacing with other circuits. Th idea is that as output volts from the transformer rise, the saturation current is increased to make the transformer less efficient and thus reduce the output volts.