[BC] unreliable old equipment query

[Gary Peterson]

One TV station was known to have gone off the air
a few times, due to an overlooked maintenance
item.  There was a manometer with integral
electrical contacts.  When sufficient air pressure
existed for tube cooling, a conductive fluid was
pushed to/beyond the level of the contacts.  More
than once, enough of the conductive fluid
evaporated, taking the transmitter off air.
Keeping the fluid level in the manometer up to
snuff should have been, but wasn't always, a
regular maintenance item.

Late one Saturday night, I was watching a movie on
a local station.  Apparently, no one in
programming had previewed the film.  I was quite
surprised to hear the F-bomb, a couple of times.
Shortly thereafter, the operator faded from film
to black.  After nearly ten minutes of black, I
called the TV station's CE, who was a good friend,
and told him what I had been seeing.  Within five
minutes, the station did their regular sign off
and left the air (about 90 minutes early).  The CE
later told me that the visual power amplifier tube
had been pretty well cooked by that episode.  An
all black picture resulted in maximum visual power
output, in the legacy NTSC television system.

Gary

"Transmitter wise (no trouble slide would be
possible unless it effected only the aural 
transmitter) the earliest transmitters were water
cooled, some with 6,000 Volts across a 2" piece of

plastic tubing made of "saran" plastic (like saran
wrap) that physically deteriorated in months and 
if not "caught" during daily inspections would
split ever so slightly and spray a mist of
distilled 
water on the RF chokes and other components, if it
just dripped it would kill drive until it 
evaporated (5 to 20 seconds) then it would repeat
when the next drop landed until the transmitter 
was shut down and the water cooling link was
replaced, perhaps a 1/2 hour job including warming
up 
the filaments again before the high Voltages could
be reapplied and broadcasting could resume.
Ron KA4INM"