On Tue, 25 May 2010 13:01:09 +1000, "Phil Allison"
wrote:

......[snip!]......

BTW:

Such resistors are of a special high voltage type approved for this purpose
and should never be replaced with general purpose ones.


.... Phil




To further Phil's point, I used to work at RCA at a television
manufacturing plant back in the '60's. In the previous 10 years from
that, a number of sets (not sure if they were RCA brand or not) had
used ordinary paper capacitors wired to the AC line. They were wax
impregnated. These were installed on the "instant-on" TV's. Instant-on
meant that the unit had power applied to part of the circuitry even
though the unit was seemingly turned off. When you turned the unit on,
most of the tubes were already hot, and the unit came on in a few
secs, instead of about half a minute. Well, some of those capacitors
failed, they overheated, and caught fire (wax burns real good), the TV
cabinet (wood/plastic), caught fire, the house caught fire, and
everyone was in bed, assuming the TV was really off.
A number of families perished.
The immediate engineering fix was to have the same wretched
capacitors enclosed in a little porcelain tube, with fire resistant
cement covering up the ends. I still have one or two in my junkbox. A
few years later they used plastic film capacitors, whose dielectric
would not burn as easily. Nowadays there are very stringent standards
that must be applied for components that are attached to the
powerline, or are in circuits where the energy is not limited to safe
values.
I always get the heebie-jeebies making up electronic units that run
off the powerline. Some are designed for hospital/medical use. So many
standards, so many things to go wrong, so many potential disasters.
That's why I feel much more secure buying approved and certified power
supplies that I can run my circuitry from.
Don't screw around with the circuitry and wiring attached to the
powerline!

Paul G.