IEEE Power & Energy Magazine - January/February 2017 - 74

The magnitude of the dc in the control winding was, in turn, controlled by
means of a relatively small resistance dimmer operated by a lever on the board.
Of course, this rheostat did introduce
some energy loss but far less than
would be the case if resistance dimmers
were used to control the lamps directly.

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These levers, by the way, were capable
of being interconnected mechanically
to provide a crude form of mastering. However, the interconnection of
a large number of levers introduced a
fair amount of mechanical friction to be
overcome. It was not possible to provide
a long enough master lever to give an

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operator sufficient mechanical advantage to accomplish this. Therefore, a
large wheel (seen at the center of the
board in Figure 1) was provided for this
purpose. The wheel was geared to the
shafts inside the board that moved the
levers, so it provided the necessary mechanical advantage.
The operation of this wheel did not
allow for extremely rapid cues. The fastest cue possible was about 15 s, which
corresponded to about 30 revolutions
of the wheel. Extremely rapid cues (for
dramatic effect) had to be made by using
the control switches associated with each
dimmer. These, in turn, switched the main
lamp circuits by means of remote contactors, and the switches themselves could
be connected to each other electrically to
provide a mastering function. The wheel,
however, was very useful for extremely
slow cues, such as sunrises or sunsets,
taking place over many minutes. Thus, it
was called the slow-motion wheel.
The Roxy Theatre was huge, with
nearly 6,000 seats, so its stage was correspondingly large and required a lot
of lighting to cover it. The total electrical load planned for the entire building
was 2,500 kW, with 780 kW allocated
for stage lighting via the Hub board.
a total of 23 watthour meters were
required for the various areas of the
building because different rates were applied to various uses (such as motors and
lights). However, another reason for such
a large number of meters was that it was
extremely difficult to calibrate watthour
meters designed for currents in excess of
800 a (the total current corresponding
to the anticipated load would have been
about 20,000 a at 120 V). Presumably,
such calibration at that time required the
inclusion of the current transformer or
shunt to be used with the meter.
The building had a total of four electric services, two for ac and two for
dc. UEL&P supplied the ac services at
208Y/120 V, three phase, and the New
York Edison Company supplied the dc
services at 120/240 V, three wire. The
main reasons for multiple services were
the high connected load and the need
for two different types of current. However, there also were requirements at
january/february 2017
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