Replacing failed powersupplies on qbus PDP-11s

Yes...but (assuming the chopper frequency is high compared to the mains frequency) there will be a period near the top of the mains AC cycle when there is a chopper-frequency component to the draw. If the filter caps are decently large, it will be tiny, but it will be present - well, possibly excepting the case where the filter caps are large enough that the time current is drawn for is less than one chopper cycle wide, in which case I'm not sure how fair it is to say that. In the presence of resonance it doesn't take much, though; the saving grace is probably that the resonance has to be both very close to exact and very low loss for the small boost each peak to be enough to produce an oscillation that grows in the long term - and neither of those is likely to be true. Not in computers, maybe. But - well, incandescent lamp dimmers. Variable-speed power hand drills. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B