[SunRescue] Monitor's Are Deadly!!!

[Martin Frost]

bobk wrote:

> I friend of mine describes how he safely discharged a monitor, was working
> on it, but then closing time came and he went home for the weekend,
> leaving it on his bench. Come monday morning, he starts working on it,
> only to get a decent ZAP. It turns out that the monitor was facing a
> window, where it received sunlight over the weekend - evidently this can
> cause a charge to build up on the tube!

I don't think it's the sunlight. Most likely dielectric relaxation in the
tube: the reason they hold a charge is that they act like capacitors. When
a capacitor is shorted, the voltage drops very quickly and the charge
doesn't dissipate as fast as you'd expect. When the short is removed,
the voltage returns to the level it should be for the remaining charge,
which can still be enough to give an unpleasant shock (remember that
some tubes get as high as 35KV normally, so you don't need a very big
proportion of that to cause problems).

I don't know what actually causes this effect, but I've heard it
referred to as `dielectric relaxation', and it can be easily
demonstrated under safer circumstances with a large capacitor, a
battery, and a voltmeter.

--m