13 Dec
2004
13 Dec
'04
11:09 a.m.
From: "Teo Zenios" <teoz(a)neo.rr.com>
Who would be using DC besides electro-platers?
Hi
I'm not sure if they had the same reason but today,
DC is actually used for long range, high voltage lines
in a number of places. DC doesn't require the insulation
to hold off quite as much voltage. It doesn't suffer
from inductive losses.
It isn't much good
for home use. In fact, lamps don't
do as well on DC as AC because of the electrical effects
of the wire evaporating ( not sure which end goes first ).
Dwight
13 Dec
13 Dec
7 a.m.
"Dwight K. Elvey" wrote:
I'm not sure if they had the same reason but
today,
DC is actually used for long range, high voltage lines
in a number of places. DC doesn't require the insulation
to hold off quite as much voltage. It doesn't suffer
from inductive losses.
But you need specialized devices not available at the end of the
19th century to produce DC in the required range (>750KV).
Back then you only had the transformer (or inefficient DC-DC
motor converters(.
It isn't much good for home use. In fact, lamps
don't
do as well on DC as AC because of the electrical effects
of the wire evaporating ( not sure which end goes first ).
Ah, the "Edison Effect". Some electrons (especially those
closer to the negative side) would jump away from the filament
and then, thanks to the electric field, land on the filament
but closer to the anode. The result was that the section of the
filament closer to the anode would be carrying more current
than say, the first third of the length of the filament (in the
- towards + direction). So filament failures almost always
occured in the last 1/3 of the filament. The fact that part
of the current traveled through the space, not the filament,
was extraordinary news in 1883, especially since the electron
was unknown at the time.
With metal filaments this became worse since some metal atoms would
migrate closer to the - terminal.
carlos.
--
Carlos E. Murillo-Sanchez
Dean of Engineering
Universidad Autonoma de Manizales, Manizales, Colombia
----
"After finding no qualified candidates for the position of principal, the
school department is extremely pleased to announce the appointment of David
Steele to the post." Philip Streifer, superintendent of schools, Barrington
RI.
11:57 a.m.
>>>> "Carlos" == Carlos Murillo
<cmurillo(a)manizales.autonoma.edu.co> writes:
> It isn't much good for home use. In fact,
lamps don't do as well
> on DC as AC because of the electrical effects of the wire
> evaporating ( not sure which end goes first ).
Carlos> Ah, the "Edison Effect". Some electrons (especially those
Carlos> closer to the negative side) would jump away from the
Carlos> filament and then, thanks to the electric field, land on the
Carlos> filament but closer to the anode. The result was that the
Carlos> section of the filament closer to the anode would be carrying
Carlos> more current than say, the first third of the length of the
Carlos> filament (in the - towards + direction). So filament
Carlos> failures almost always occured in the last 1/3 of the
Carlos> filament. ...
Interesting! That suggests that DC should be no big problem for
halogen lamps (incandescents with iodine vapor fill).
paul
5:49 p.m.
On Mon, 13 Dec 2004, Paul Koning wrote:
Interesting! That suggests that DC should be no big
problem for
halogen lamps (incandescents with iodine vapor fill).
How do you figure? There's still evaporation in halogens also, just not
as much as in incandescents, right?
--
Sellam Ismail Vintage Computer Festival
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14 Dec
14 Dec
4:29 a.m.
>>>> "Vintage" == Vintage
Computer Festival <vcf(a)siconic.com> writes:
Vintage> On Mon, 13 Dec 2004, Paul Koning wrote:
> Interesting! That suggests that DC should be no
big problem for
> halogen lamps (incandescents with iodine vapor fill).
Vintage> How do you figure? There's still evaporation in halogens
Vintage> also, just not as much as in incandescents, right?
Halogen lamps have a negative feedback system: the tungsten that
evaporates is carried back to the hot spots of the filament (which are
the thin spots). That's why they last so much longer.
The Edison effect says that the positive end gets hotter so it wears
faster -- but the iodine says that the tungsten will be brought back
predominantly to that end. So that (largely) cancels out.
The other aspect, as Dwight Elvey pointed out, is that modern light
bulbs are not vacuum. I don't know how halogen bulb pressures compare
with "regular" ones -- they may well be higher.
paul
13 Dec
13 Dec
12:34 p.m.
On Mon, 13 Dec 2004, Carlos Murillo wrote:
I'd heard of the effect, but not for a long time, and probably paid little
attention to it :-)
So, how pronounced is this DC-filament effect? If I collect
dead lightbulbs from my cars, should I see filaments with gaps
burned towards the ground end more often than not?
(Tapered filaments would fix this.)
It isn't
much good for home use. In fact, lamps don't
do as well on DC as AC because of the electrical effects
of the wire evaporating ( not sure which end goes first ).
Ah, the "Edison Effect". 
12:59 p.m.
So, how pronounced is this DC-filament effect? If I
collect
dead lightbulbs from my cars, should I see filaments with gaps
burned towards the ground end more often than not?
I have noticed that if a car lightbulb blows, it tends to part at the
bit where one "straight" bit of the filament goes into the helical part.
I think this may be more down to mechanical stress.
Gordon.
3:52 p.m.
Ah, the "Edison Effect". Some electrons
(especially those
closer to the negative side) would jump away from the filament
and then, thanks to the electric field, land on the filament
but closer to the anode.
In a few bulbs, if the geometry is right, they will magically turn into
very low power magnetrons.
William Donzelli
aw288(a)osfn.org
7:23 p.m.
On Mon, 13 Dec 2004, William Donzelli wrote:
EEK! Cool! electromagnetic whistles!
I shudder to think how this effect was discovered... talk about
heisenbugs! Imagine some poor microwave receiver person trying
to find a loss of sensitivity, birdies, spurious output... and
finding out it's some goddamn FRONT PANEL LIGHT BULB!
Do you have any references to this? I have a friend who would
appreciate such horrors...
Ah, the
"Edison Effect". Some electrons (especially those
closer to the negative side) would jump away from the filament
and then, thanks to the electric field, land on the filament
but closer to the anode.
In a few bulbs, if the geometry is right, they will magically turn into
very low power magnetrons. 
14 Dec
14 Dec
2:40 a.m.
On Mon, 13 Dec 2004, William Donzelli wrote:
In a few
bulbs, if the geometry is right, they will magically turn into
very low power magnetrons.
EEK! Cool! electromagnetic whistles!
I shudder to think how this effect was discovered... talk about
heisenbugs! Imagine some poor microwave receiver person trying
to find a loss of sensitivity, birdies, spurious output... and
finding out it's some goddamn FRONT PANEL LIGHT BULB!
10:52 a.m.
On Tue, 14 Dec 2004 gordonjcp(a)gjcp.net wrote:
... which would, of course, magically cure itself when you approached the
unit, because the capacitance from the bulb to your hand would kill the
oscillations.
The stuff nightmares (and careers) are made of...
One of the worst heisenbugs I can recall was a tape drive
(unknown manu) on the Nova 1200 development system at Ocean
Research Equip., late 1970's. Just an ordinary drive, somewhat
low in the rack. It would "randomly" fail, tape went slack,
but only in the afternoon.
The heisenbug aspect was: it would work fine when you were
standing in front of it. If you walked away, slack tape.
The problem was found when we determined it worked also, in
the afternoon, unattended, with it's smoked plexi door closed,
which was always left open because it was annoying to open and
close all the time. Turns out it was a ray of afternoon sun
beaming in the window directly into the tape-in-place sensor
near the head/capstan area.
On Mon, 13 Dec
2004, William Donzelli wrote:
In a few
bulbs, if the geometry is right, they will magically turn into
very low power magnetrons.
EEK! Cool! electromagnetic whistles!
I shudder to think how this effect was discovered... talk about
heisenbugs! Imagine some poor microwave receiver person trying
to find a loss of sensitivity, birdies, spurious output... and
finding out it's some goddamn FRONT PANEL LIGHT BULB!
11:30 a.m.
Tom Jennings wrote:
One of the worst heisenbugs I can recall was a tape
drive
(unknown manu) on the Nova 1200 development system at Ocean
Research Equip., late 1970's. Just an ordinary drive, somewhat
low in the rack. It would "randomly" fail, tape went slack,
but only in the afternoon.
The heisenbug aspect was: it would work fine when you were
standing in front of it. If you walked away, slack tape.
The problem was found when we determined it worked also, in
the afternoon, unattended, with it's smoked plexi door closed,
which was always left open because it was annoying to open and
close all the time. Turns out it was a ray of afternoon sun
beaming in the window directly into the tape-in-place sensor
near the head/capstan area.
Many years ago (oh, ok, about 20) when I was not even yet a spotty
teenage geek, I was playing about trying to coax some life from an old
valve radio. Poking about with high-impedance headphones suggested that
the problem was in the final stage of the audio amp. It would play
quietly, getting fainter, until eventually there was nothing...
So, I figured I should be seeing about -6 volts on the control grid wit
respect to the cathode. Whip out my Dad's AVO 8, apply red croc clip to
the cathode pin, apply black croc clip to the grid and *DAMN THAT WAS
LOUD*!!!
Reduce volume to a sensible level, shrug, and listen to the radio - took
a lot longer to get faint, as I bumped the volume up and up, but
eventually it faded completely. Volume to minimum, probe grid pin,
slowly increase volume, worked for a few minutes more.
Hmm.
Consult rough sketch of the circuit around the output amp that I'd
drawn. What was this funny 1M resistor from the grid to ground? And
why was it reading damn near open? Of course, the grid leak resistor,
without which the control grid would build up enough negative charge to
cut off the valve completely...
Gordon.
11:44 a.m.
On Tue, 14 Dec 2004, Gordon JC Pearce wrote:
Consult rough sketch of the circuit around the output
amp that I'd drawn.
What was this funny 1M resistor from the grid to ground? And why was it
reading damn near open? Of course, the grid leak resistor, without which the
control grid would build up enough negative charge to cut off the valve
completely...
A non-subtle reminder of where those names come from! Leak indeed...
You could have just left the VM on it :-)
12:44 p.m.
I shudder to think how this effect was discovered...
talk about
heisenbugs! Imagine some poor microwave receiver person trying
to find a loss of sensitivity, birdies, spurious output... and
finding out it's some goddamn FRONT PANEL LIGHT BULB!
I would suspect a bigger bulb would be needed. High current is needed to
make the magnetic field.
Do you have any references to this? I have a friend
who would
appreciate such horrors...
It was discussed amongst the tube geeks a couple of years ago, I think at
the big Rochester radio show.
William Donzelli
aw288(a)osfn.org
7155
days inactive
7156
days old
14 comments
8 participants
participants (8)
-
aw288＠osfn.org -
cmurillo＠manizales.autonoma.edu.co -
dwight.elvey＠amd.com -
gordon＠gjcp.net -
gordonjcp＠gjcp.net -
pkoning＠equallogic.com -
tomj＠wps.com -
vcf＠siconic.com