On Thu, 14 Jul 2005, Roy Lewallen wrote:

Date: Thu, 14 Jul 2005 13:27:57 -0700
From: Roy Lewallen
Newsgroups: rec.radio.amateur.homebrew
Subject: QUESTION: Fun with Svetlanas or Staying alive with kV power
supplies

Don't forget about "soak", also known as dielectric absorption or dielectric
hysteresis. In some capacitors, particularly electrolytics, charge "soaks"
into the dielectric and can take from seconds to days to work its way out.
The result is a "discharged" capacitor that seems to spontaneously recharge
itself. (One story I heard during my broadcast days was someone who put a
screwdriver across a "discharged" capacitor.

Yep, I can vouch for this effect. I've seen it, too. Short the cap with
alligator clip-tipped wire for a few seconds if you want that voltage down
to microvolts. I think it is not "soak" but simple RC time constant decay.
Just like radioactive half-life. Residual voltage on a cap _never_ goes to
true zero, only according to the decay equation. However, there is a
so-called "electret" effect which really sounds like your "soak" effect.

After he picked himself up off
the floor, he found just the handle of the screwdriver. He was lucky his eyes
weren't hit with molten metal. You'll often find large capacitors stored with
a shorting wire across them -- a good idea.)

D'arsonval meters, especially sensitive ones, are also best stored with a
shorting wire accross the terminals.

I recommend leaving a heavy
cliplead in place across the high voltage capacitors for the entire time
you're working on the unit. Put some tape over the on/off switch and/or a tag
on the plug to remind you to remove it before turning the power back on.

As a side note, the aquadag coating of a CRT is notorious for this. I've
gotten a healthy bite off a CRT the day after it was discharged for an hour
or more with a cliplead.

Roy Lewallen, W7EL