[cctalk] Re: Ferroresonant transformer mystery

Recently I got a nice and complete PDP-8/s from the US. The power supply uses a ferroresonant transformer which in addition to the standard primary and secondary windings has a separate 2.3H winding connected in series to a 2uF 660VAC capacitor forming a resonant "tank" circuit. The transformer's secondary side and the resonant circuit are operated in saturation. There is a magnetic shunt to prevent the primary side going into saturation as well. It accepts a wide input voltage range, but is very sensitive to the input frequency of 60Hz. This is quite a nice if not elegant design for the period in question, but maybe not the most efficient.