In message , ARW
writes
On 18/12/2019 08:46, Ian Jackson wrote:
In message , "Brian Gaff (Sofa 2)"
writes
Have you heard some of the RFI generated by Christmas lights these days?
From* gently gurgling to whining noises. I suppose they all have
dirt cheap
switch mode supplies with a convenient aerial to radiate the crap
built in.

'Twas ever thus. It was around 1950 that we got our first 12-bulb set
of Christmas lights. I think they were originally 'always on', but
you could buy a flasher bulb that contained bi-metal make-break
contacts. The regular wideband RF splat as the lights innocently
turned on and off carried a considerable distance, and when listening
to the radio (no TV in those days) the flasher bulb had to be
temporarily replaced with a normal type. [I still have the set, but
about half of the bulbs are blown. The only way to run them now is to
put some silver paper in the dead bulb sockets, screw in the dead
bulbs, and run the remainers from a reduced voltage.]

Rewire them to parallel and use a 12V power supply.

They would be a bit dim. 12 bulbs across a 240V mains means that they
are each 20V. Also, running even six in parallel would mean a lot of
bulky wire. Instead, I use a variac (variable output mains transformer).

Note that modern incandescent bulbs (if they haven't all by now been
succeeded by LEDs!) have a fail-safe loop of wire around the filament
supports. If a filament fails, the supports spring apart, and the wire
loop provides a S/C across the bulb - so the remaining bulbs in the
string stay lit (albeit a little brighter).
--
Ian