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Re: Rank AC Power



I'd be curious to know how you're measuring the harmonic distortion on the
power line.  Very few power transformers produce outputs that are perfectly
harmonic-free, and there is no real need for them to, since it's a fiction
that commercial power alternators produce pure sine-waves to begin with!
 Viewed from the point where the power enters the equipment, any type of
rectifier distorts the AC power waveform, whether it is on the other side of
an equipment power transformer or directly connected.  Switching power
supplies make a much bigger mess of things than linear ones, and
ferroresonant voltage regulating transformers are also quite notorious for
distorted output waveforms under load.  Of course none of this matters to the
equipment as long as there is adequate filtering and sheilding to keep the
"trash" out of the DC supplies.  It is for this reason, by the way that Rank
puts electrostatic sheilding between the primary and secondary of its power
transformers.  Proper grounding of this sheilding is one of those things that
sometimes gets overlooked, by the way.

The solid state relay used in the Rank power box is a zero-crossing type (or
should be), which means that it should not be messing up the power
significantly.  Of course these devices can and do go bad--particularly if
the machine took a lot of power hits--in which case all sorts of weird things
might happen.  However, the wiring in the box can sometimes make enough of a
magnetic field to cause subtle positional hum problems, since the box is
directly beneath the CRT.  For this reason, you'll often see a mu-metal
sheild under the CRT in some Ranks, or the power box will be moved to the
bottom of the cabinet.

Christopher Bacon