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Re: Terrified Parents



Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: dhmccauley-at-spacecatlighting-dot-com
 >
 > Definitely an urban legend.  HV probes always have dividers built in them.
 > Thats the whole purpose of a HV probe.   If it didn't have the divider, it
 > would basically be
 > just a metal rod with an insulated handle.
 >
 > However, i do have a story that is true.  A technician at my company was
 > working with a radar transmitter in the high voltage cabinet, and was taking
 > oscilloscope measurements from a
 > modulating high voltage deck.  The deck itself is low voltage (28VDC with
 > +/-1000VDC for the grid modulating system), but the entire deck is floated
 > at the cathode voltage of the TWTs
 > which is about 45-60kV depending on TWT.  Anyways, the oscilloscope was
 > being floated on top of the deck to measure something in the deck, and the
 > technician went to change a setting
 > on the scope and . . . well . . . you can imagine what happened next.
 >
 > Dan

	Sounds remarkably like an event I was involved in at Hughes Aircraft,
about 1971.  We had a high-power Ku Band TWT operating at a cathode
voltage of -65 kV and wanted to look at the grid modulation voltage.
One of the guys found someone who would rent us a battery-operated scope
with enough frequency response.  Stuff was set up and the scope was hung
from the ceiling with lacing cord.  The transmitter breadboard was
operated in a big tank of oil about 3' square by 6' long and scope was a
couple of inches above the oil.  The thing worked pretty well but one
day someone managed to arc the case of the scope to ground!  It made
quite a bang.  The interesting part is that the scope still worked and
was returned to the renting agency with no mention of what had happened
and no subsequent complaints from them.

	I often think about this when guys are trying to figure out how to
monitor what's going on at the HV terminal.  Maybe someone could rig a
transparent (wire screen?) toroidal terminal big enough to hold the
scope and then watch the scope trace through the openings.

Ed