Paul Burridge wrote:
Hi all,
Anyone got any high-current/low-voltage horror stories they'd care to
share? You know; where your messin' about with a car battery or
something like that and forget to take your watch off or whatever.
p.
When I graduated from highschool, 1967, I started work for a company
called Standard Plastic Products. What we really did was make those
plastic and cardboard Barbie cases. These were heat sealed with
RF Energy. Lots of it.
The work area had about 50 sealing machines. These units were Class-C
RF oscillators and ranged from 25 to 60 KW. Yes, that is Kilo Watts.
Each unit had a large ceramic tube that had a base of around 6 - 8
inches in diameter. The larger units had tubes with large heat sink
hats which required a chimney to remove the heat. The RF energy was
applied to two copper platens that performed the sealing.
My job, along with three other techs, was to keep these machines
working. The most common problem with these things was blowing fuses,
dirty coupling capacitor clips, and some pretty spectacular blowouts
on the platens when the material got too thin.
The real problem was that, you had to reach into the units from the
back to get to the fuses or the coupling caps. The units had
power interlocks, so you couldn't activate with the back open
This was suppose to disable all power, remove the plate voltage,
and allow any charge to bleed off. But there were a few units where
the bleeder circuits did not work properly. This usually left a few
thousand volts on the plates of the tubes. You learned real quickly
to grip your adjustable wrench with your cardboard fuse pullers and
short the plate to ground. It was a heck of a blast and after 2 or
3 times, the unit was safe to work on.
Although I never heard of anyone actually comming in contact with
the voltage, because we were always on our toes, but I am sure that
it would have done some damage. I doubt the government would let
them get away with something like that now.
And you want to talk about QRM, these things oscillated around 27 MHz.
--
Martin E. Meserve
http://www.k7mem.150m.com