Nick Flowers Posted May 11, 2020 Report Share Posted May 11, 2020 My first feature film involved powering the camera (Mitchell BNC) off a rotary converter, which supplied a 50Hz pulse for the Nagra as well. I suppose the rotaries have been consigned to history books, but I was glad to have had experience with them. Here is the Wiki page that describes them: https://en.wikipedia.org/wiki/Rotary_converter The one I used for film work had a couple of beefy 12 volt lorry batteries as the power source, which powered a DC motor. This turned a three phase alternator which supplied the energy to power the camera motor. I assume that the rotary supplied 110 volts (I can't remember) for the American Mitchell; but the pulse for the Nagra was 50Hz.. There was an automatic system for keeping the machine at the right speed, which varied with load, although there was also a knob for manual regulation; and the frequency of the pulse was displayed on a reed meter, which vibrated a bank of reeds, each carefully cut to the right length to vibrate most at its indicated frequency, with 50Hz in the middle and + or - 0.1 Hz on either side.I expect that in the USA this would have been 60Hz. In a studio, this three phase power supply would have been available off the wall boxes, but we were shooting in a disused factory, so it was location equipment. Nevertheless, it took two men to shift the box containing the equipment. The operation of the rotary guaranteed the four man sound crew: the sound maintenance guy watched over the rotary, the sound camera operator would operate the Nagra (only a few years previously he would have operated a Sound Camera), the boom op swung the boom (Fisher or Mole) and the mixer twiddled the knobs. Four man sound crew. Luxury! The sequence of events when shooting would be for the 1st Assistant to shout "Turn over," and the rotary would be switched on. After about 4 or 5 seconds it would have got up to speed and stabilised, and the operator would call out "Speed", and the board would go on. There were other way of getting the 3 phase supply on location, using big capacitors, but these were unmanned and therefore of little interest. Quote Link to comment Share on other sites More sharing options...
John Blankenship Posted May 11, 2020 Report Share Posted May 11, 2020 Here's an example of a vibrating reed frequency meter with reeds a half Hertz apart: Quote Link to comment Share on other sites More sharing options...
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