26 Apr
2011
26 Apr
'11
10:24 a.m.
At 12:00 -0500 4/26/11, ard wrote:
One of the easiest things to sue for this are low
voltage filament
lamps 12V car bulbs (say a 12V 5W taillight bulb) is fine for a 12V
supply. And probalby fine for a 15V supply too (yes, the bulb will have a
short life at the higher voltage, but not so short as to worry you). For
the 5V line, a 6V bulb is the best thing to use, many older cars had 6V
electrics nad you may well be able to get a 6V 30W bulb (which will draw
around 5A) from a vintage car parts company. I bought a couple of
headlight bulbs (each with a apr of 30W or so filaments and a couple of
stop/taillight bulbs (5W and 21W filamnets). That gives me a good
selection of laod currents (and yes, I once parallel to two filaments of
a headleam bubl to give a load drawing somewhat more than 10A to test a
large SMPSU).
FWIW, bicycles use a wide variety of bulbs, in a wide variety of
voltage ratings. Here's one page
http://www.reflectalite.com/halogenpage.html
listing a bunch of them, in voltages from 2.2 V to 6 V and wattages
from 1.25 W to 20 W. (Not a recommendation, they were
just what came
up first when I googled "bike headlight bulbs". I'd
actually
recommend your local brick-and-mortar bike shop, who could probably
use the business...)
I don't expect these are very cost-effective, but they should be more
available (for the time being, anyway, until LED's take over there
too) than antique-auto bulbs. But you may want/need to run several in
parallel to add up the required power.
--
- Mark 210-379-4635
-----------------------------------------------------------------------
Large Asteroids headed toward planets
inhabited by beings that don't have
technology adequate to stop them:
Think of it as Evolution in Fast-Forward.
26 Apr
26 Apr
10:55 a.m.
It would seem to me that if you needed a dummy load for a power
supply (and couldn't scrape up a bunch of power resistors), it would
make the most sense to use the highest voltage incandescent lamps
that you have at your disposal.
The reason is quite simple--tungsten-filament lamps (not that I
expect anyone to have any carbon-filament ones) have a very steep
resistance-temperature curve (higher "hot" resistance).
Instead of a automotive lamp, use a regular 120V (or 220V)
incandescent(s). The ratio of hot-to-cold resistance will be much
reduced (on a lamp operated at the rated voltage, hot-to-cold
resistance is usually about 15 to 1).
Or better yet, use a nichrome heating element from an old hair dryer
or aquarium heater. Nicrhome V wire has only a 6% increase in
resistance between 68F and 1600F.
Just saying...
--Chuck
12:17 p.m.
It would seem to me that if you needed a dummy load for a power
supply (and couldn't scrape up a bunch of power resistors), it would
make the most sense to use the highest voltage incandescent lamps
that you have at your disposal.
The reason is quite simple--tungsten-filament lamps (not that I
expect anyone to have any carbon-filament ones) have a very steep
resistance-temperature curve (higher "hot" resistance).
Tugsten filament lamps approximate a constant current load over quite a
range of voltages (am I the only person to rememebr the baretter?).
So your 110V 100Q bulb will draw a little under 1A at its rated voltage.
At a lower voltage it will still draw only 1A.
Let's work it out a little more accurately. At 110V, a 100W bulb draws
0.91A. If your figure for a hot-cold resistance swing of 15 times is right
(and it sounds it, we can estimate that the hot resistance is about 121
ohms. The cold resistance is 1/15 of that, or 8.07 ohms. Connect that
across a 5V PSU and it will draw 0.62A. Not really enough for a dummy load.
A 6V 6W bulb (which is easy to get) would draw 1A and be most suitable.
Or better yet, use a nichrome heating element from an
old hair dryer
or aquarium heater. Nicrhome V wire has only a 6% increase in
resistance between 68F and 1600F.
If you are really crazy, use containers of salt water with suitable
electrodes in them :-). Just don't knock them over and spill the liquid
into the machine under test.
-tony
12:40 p.m.
On Tue, Apr 26, 2011 at 08:17:26PM +0100, Tony Duell wrote:
>
...
> The reason is quite simple--tungsten-filament
lamps (not that I
> expect anyone to have any carbon-filament ones) have a very steep
> resistance-temperature curve (higher "hot" resistance).
HP remembered this.
- Diane
--
- db at FreeBSD.org db at db.net http://www.db.net/~db
Why leave money to our children if we don't leave them the Earth?
12:56 p.m.
> The
reason is quite simple--tungsten-filament lamps (not that I
> expect anyone to have any carbon-filament ones) have a very steep
> resistance-temperature curve (higher "hot" resistance).
HP remembered this. 
1:49 p.m.
On 4/26/11 3:56 PM, Tony Duell wrote:
Indeed they did. In the Mdoel 200 Audio Oscillator for one thing ;-)
Well, "H" did, anyway. ;)
I have two Model 200s. I will restore them to museum-quality (both
aesthetically and functionally) when I get my new workspace.
-Dave
--
Dave McGuire
Port Charlotte, FL
> The reason is quite simple--tungsten-filament
lamps (not that I
> expect anyone to have any carbon-filament ones) have a very steep
> resistance-temperature curve (higher "hot" resistance).
HP remembered this.
27 Apr
27 Apr
11:33 a.m.
> The reason
is quite simple--tungsten-filament lamps (not that I
> expect anyone to have any carbon-filament ones) have a very steep
> resistance-temperature curve (higher "hot" resistance).
HP remembered this.
7:52 p.m.
New subject: Dummy loads
On 4/27/11 2:33 PM, Tony Duell wrote:
Beware, I've never seen one in good condition. The crinkle-finish
paint is always flaking off. :-( I think they're worth owning, though,
for their history. It's a great design that really withstood the test
of time.
I did recently happen upon an HP 210A "square wave generator". I say
that in quotes because it's actually just a clipped amplifier that one
drives (switch-selectably) from the 60Hz line or from an external
sine-wave generator. Its styling matches that of the 200 series, as
does its rock-solid quality of construction.
-Dave
--
Dave McGuire
Port Charlotte, FL
I have two
Model 200s. I will restore them to museum-quality (both
aesthetically and functionally) when I get my new workspace.
Nice! It's an insturment I'd like to own, and they're nto rare (or even
that expensive) on E-bay, but I think shipping one across the Pond might
be a problem. One day perhaps....
28 Apr
28 Apr
11:22 a.m.
New subject: Dummy loads
On 4/27/11 2:33 PM, Tony Duell wrote:
Beware, I've never seen one in good condition. The crinkle-finish
That adds to the fun :-). I am interested in this unit for its historical
significance, I have n AF signal gneraotr, and anyway it's not an
instruemtn I have too much real use for.
I would probably repaint one f I owned it, but it wou;d be top priority,
Getting the electroncs back to rights (meaming as close to origianl as I
can), would be.
I
have two Model 200s. I will restore them to museum-quality (both
aesthetically and functionally) when I get my new workspace.
Nice! It's an insturment I'd like to own, and they're nto rare (or even
that expensive) on E-bay, but I think shipping one across the Pond might
be a problem. One day perhaps.... paint is always flaking off. :-( I think they're
worth owning, though,
for their history. It's a great design that really withstood the test
of time.
Indeed it did.
-tony
11:50 a.m.
New subject: Dummy loads
On 4/28/11 2:22 PM, Tony Duell wrote:
Beware, I've never seen one in good condition. The crinkle-finish
That adds to the fun :-). I am interested in this unit for its historical
significance, I have n AF signal gneraotr, and anyway it's not an
instruemtn I have too much real use for.
Same here. I have an HP 3325A, a wonderful unit. One thing I want
to do with the Model 200 is to analyze its performance with modern
equipment and techniques. That has been done to death, but *I* haven't
done it, and I'm interested in seeing the results directly for
educational value.
I have
two Model 200s. I will restore them to museum-quality (both
aesthetically and functionally) when I get my new workspace.
Nice! It's an insturment I'd like to own, and they're nto rare (or even
that expensive) on E-bay, but I think shipping one across the Pond might
be a problem. One day perhaps.... I would probably repaint one f I owned it, but it
wou;d be top priority,
Getting the electroncs back to rights (meaming as close to origianl as I
can), would be.
If I can match the original paint color, I'll probably repaint mine
as well. Ditto on the prioritization.
-Dave
--
Dave McGuire
Port Charlotte, FL
26 Apr
26 Apr
2:49 p.m.
On 26 Apr 2011 at 15:40, Diane Bruce wrote:
On Tue, Apr 26, 2011 at 08:17:26PM +0100, Tony Duell
wrote:
It was common knowledge in the 1930s. I have a "Radio Engineering"
handbook from the late 30s that shows the consutruction of an audio
signal generator using a common panel lamp for temperature
compensation.
--Chuck
>
...
> The reason is quite
simple--tungsten-filament lamps (not that I
> expect anyone to have any carbon-filament ones) have a very steep
> resistance-temperature curve (higher "hot" resistance).
HP remembered this. 
27 Apr
27 Apr
12:01 a.m.
Chuck Guzis [cclist at sydex.com] wrote:
It was common knowledge in the 1930s. I have a "Radio Engineering"
handbook from the late 30s that shows the consutruction of an audio
signal generator using a common panel lamp for temperature
compensation.
I saw the technique used once in a Practical Electronics article
sometime
in the 1980s (or thereabouts). So I don't think it was forgotten, just
not used very often.
Antonio
arcarlini at iee.org
7:20 a.m.
New subject: Dummy loads
On 04/27/2011 03:01 AM, arcarlini at iee.org wrote:
Chuck Guzis [cclist at sydex.com] wrote:
That was a wide spread application for negative feedback and
level controls.
My Measurements M803A signal generator (6CW4 nuvister for Osc)
has a 7W sewing machine lamp in the solid state audio oscillator.
I've seen that same arrangement used in many audio generators
of the Wein Bridge type. I've also seen thermistors with both positive
and negative temperature coefficients used for that purpose.
It's not forgotten and its old.
Allison
It was common knowledge in the 1930s. I have a
"Radio Engineering"
handbook from the late 30s that shows the consutruction of an audio
signal generator using a common panel lamp for temperature
compensation.
I saw the technique used once in a Practical Electronics article
sometime
in the 1980s (or thereabouts). So I don't think it was forgotten, just
not used very often.
Antonio
arcarlini at iee.org
12:50 p.m.
Chuck Guzis [cclist at sydex.com] wrote:
I was very common ito the transistor/IC era. OK, sometimes you used a
thermistor not a light bulb, but the principle was the same. A couple of
examples off the top of my head :
The Philips EE1003/1004 kits have a project ot make a Wien bridge
oscillator using a filament lamp to stabilise the gain. That was all
discrete transistors
There was a Heathkit analoge electronics trainer (in the same series as
the well-known 6800 computer one), which has a built-in signal generaotr.
It's a Wein bridge circuit using an op-amp for the ampliifer, agian with
a small filament lamp tocontrol the gain.
There was a very xommon small audio sig-gne used in schools and
university undergraduate labs over here. Yes, a Wein bridge (although
oddly the capitro, not the resistor, was the variable part), using a
thermisotr for gain control.
There must be many others....
-tony
It was common knowledge in the 1930s. I have a "Radio Engineering"
handbook from the late 30s that shows the consutruction of an audio
signal generator using a common panel lamp for temperature
compensation.
I saw the technique used once in a Practical Electronics article
sometime
in the 1980s (or thereabouts). So I don't think it was forgotten, just
not used very often. 
26 Apr
26 Apr
2:44 p.m.
New subject: Dummy loads
On 4/26/2011 2:17 PM, Tony Duell wrote:
<snip>
I'm sure it's just a typo, and I apologize in advance for being too dumb
to figure it out, but what is a baretter? (Sounds quite interesting,
but an internet search couldn't figure it out either, except for some
things in languages I don't understand.)
Thanks,
Charlie C.
The reason is
quite simple--tungsten-filament lamps (not that I
expect anyone to have any carbon-filament ones) have a very steep
resistance-temperature curve (higher "hot" resistance).
Tugsten filament lamps approximate a constant current load over quite a
range of voltages (am I the only person to rememebr the baretter?).
27 Apr
27 Apr
12:33 p.m.
New subject: Dummy loads
On 4/26/2011 2:17 PM, Tony Duell wrote:
<snip>
I'm sure it's just a typo, and I apologize in advance for being too dumb
to figure it out, but what is a baretter? (Sounds quite interesting,
It is a typo, or rather a mis-spelling. It should be 'barretter;.
A barretter is a constant-current device, essentially a special type of
filament lime. Often the filament was iron wire in a hydrogen-filled bulb
(or so I've read). The current floowing though the device was fairly
constant for quite a wide range of voltages across it.
Some UK series-string radio sets had one in series with the heater chain
(rather than a dropping resistor) so that the heater current would be
correct for jsut about any mains input voltage.
The were also used as a ballast for the Nernst glower in some IR sources
(which is where I first came across one at school [I managed to convicne
the powers that be that getting me to chase a ball around an area of
grass was a waste of everyone's time, so I got to fiddle with electronics
stuff instead. Getting the old IR source to work again was just one of
the many things I tried]
FWIW, if you have an old device using a barretter, you can often use a
mains-voltage lamp to replace it. I am pretty sure I used a normal 60W
bulb (so 0.25A at 240V) to replace a 0.3A barrretter in said IR source.
-tony
The
reason is quite simple--tungsten-filament lamps (not that I
expect anyone to have any carbon-filament ones) have a very steep
resistance-temperature curve (higher "hot" resistance).
Tugsten filament lamps approximate a constant current load over quite a
range of voltages (am I the only person to rememebr the baretter?).
29 Apr
29 Apr
10:39 p.m.
New subject: Barretter (was Dummy loads)
On 4/27/2011 2:33 PM, Tony Duell wrote:
OK, thanks.
Usually the search engines guess better than on this one.
After all, only one "r" was missing! Neither Ixquick nor Google guessed
the other spelling though.
On 4/26/2011 2:17 PM, Tony Duell wrote:
<snip>
I'm sure it's just a typo, and I apologize in advance for being too dumb
to figure it out, but what is a baretter? (Sounds quite interesting,
It is a typo, or rather a mis-spelling. It should be 'barretter;. The
reason is quite simple--tungsten-filament lamps (not that I
expect anyone to have any carbon-filament ones) have a very steep
resistance-temperature curve (higher "hot" resistance).
Tugsten filament lamps approximate a constant current load over quite a
range of voltages (am I the only person to rememebr the baretter?).
A barretter is a constant-current device, essentially a special type of
filament lime. Often the filament was iron wire in a hydrogen-filled bulb
(or so I've read). The current floowing though the device was fairly
constant for quite a wide range of voltages across it.
Some UK series-string radio sets had one in series with the heater chain
(rather than a dropping resistor) so that the heater current would be
correct for jsut about any mains input voltage.
The were also used as a ballast for the Nernst glower in some IR sources
(which is where I first came across one at school [I managed to convicne
the powers that be that getting me to chase a ball around an area of
grass was a waste of everyone's time, so I got to fiddle with electronics
stuff instead. Getting the old IR source to work again was just one of
the many things I tried]
Wow, I'm sure you are correct in some incarnations of the device, but my
quick search shows Fessenden using it as what sounds like an AM
detector. There is also mention of using it for microwave power
measurements. I suspect these are very delicate versions of the ones
used as constant current devices with probably a different method of
construction. One I found (Wikipedia - yes I know that is suspect)
starts with a .003 inch diameter platinum wire encased inside a 0.1 inch
diameter silver wire. Then the combination is drawn down until the
outer silver wire is only .002 inch in diameter. By this point, the
platinum is very thin indeed. Next a bit of the silver is etched away,
leaving a very thin section of platinum as the operational element. The
thing is then put into an evacuated glass bulb with the silver leads
brought out. Supposedly the tiny platinum section can change resistance
quickly enough to follow the audio modulation but not the RF carrier on
which it is superimposed. Probably not used too much in classic
computers, but fascinating nevertheless.
FWIW, if you have an old device using a barretter, you
can often use a
mains-voltage lamp to replace it. I am pretty sure I used a normal 60W
bulb (so 0.25A at 240V) to replace a 0.3A barrretter in said IR source.
-tony
26 Apr
26 Apr
2:53 p.m.
On 26 Apr 2011 at 20:17, Tony Duell wrote:
A 6V 6W bulb (which is easy to get) would draw 1A and
be most
suitable.
Unless inrush current matters (as it can on many PSUs with
overcurrent protection). At the moment you switch the PSU on, that
lamp will draw considerably more current until it reaches operating
temperature. My point was that by using a higher-voltage lamp, the
difference between "cold" and "operating" resistances is much less.
--Chuck
27 Apr
27 Apr
12:38 p.m.
On 26 Apr 2011 at 20:17, Tony Duell wrote:
The output cirucit of most PSUs has a sizeable capacitro across the
output terminals. That will take a high current at switch-on too.
I've never had a PSU that has a problem powering a suitably-rated
filament lamp. Such PSUs probably exist, but it's not somethign to worry
about. Of course if the PSU won't start up, then you have to investigate
why, and it might be the inrush current of the load (but if it is, I
would suspect there are other problems with the PSU)
A 6V 6W bulb (which is easy to get) would draw 1A
and be most
suitable.
Unless inrush current matters (as it can on many PSUs with
overcurrent protection). At the moment you switch the PSU on, that lamp will draw considerably more current until it
reaches operating
temperature. My point was that by using a higher-voltage lamp, the
difference between "cold" and "operating" resistances is much less.
Ture, but given that a 110V 110W bulb is essntially an 8 ohm resistor
when cold, you might as well use a, 8.2 Ohm wire-wound resistor across
the 5V terminals. It will dissipate a little over 3W (and for testing, I
would be suprised if a 3W 8.2 Ohm resistor wasn't adequate).
-tony
26 Apr
26 Apr
11:59 a.m.
FWIW, bicycles use a wide variety of bulbs, in a wide
variety of
voltage ratings. Here's one page
Good suggestion!
Having never riden a bicycle (and never intendign to), I am not sure of
the rules over here now, but IIRC at one time only specific voltages and
wattages of bulbs were permitted in bicycle lamps in the UK. What a daft
regulation!. So such bulbs may not be as easy to get over here as elsewhere.
But I suspect 6V tungsten-halogen bulbs are available without too much
difficulty and would make ideal dummy loads
http://www.reflectalite.com/halogenpage.html
listing a bunch of them, in voltages from 2.2 V to 6 V and wattages
from 1.25 W to 20 W. (Not a recommendation, they were just what came
A 6V 20W blub would draw pver 3A, and would be a suitable dummy load for
many PSUs.
[...]
I don't expect these are very cost-effective, but
they should be more
available (for the time being, anyway, until LED's take over there
too) than antique-auto bulbs. But you may want/need to run several in
Admitteedly it was about 10 years ago that I bougth them but I had no
problems getting 6V car bulbs then. I suspect they are still made if you
hunt around.
parallel to add up the required power.
Sure, and that's easy to do...
-tony
12:52 p.m.
Admitteedly it was about 10 years ago that I bougth
them but I had no
problems getting 6V car bulbs then. I suspect they are still made if you
hunt
around.
Indeed, I had no trouble locating some here:
http://www.autobulbsdirect.co.uk/, including bulb holders too (I didn't
realise you could get generic bulb holders, I thought they would be specific
to each car and so quite expensive, thankfully this is not the case).
Regards
Rob
27 Apr
27 Apr
11:15 a.m.
Indeed, I had no trouble locating some here:
http://www.autobulbsdirect.co.uk/, including bulb holders too (I didn't
Thanks for the URL. They seem to sell some useful stuff.
I noticed that the 6V bulbs are mostly listed as 'scooter bubls' which
suggests a motorcycle shop would be a place to try for them. Even if they
didn;'t stock them they might be able to order them.
realise you could get generic bulb holders, I thought
they would be specific
to each car and so quite expensive, thankfully this is not the case).
The car-specifc ones come as part of the complete light cluster, and are
expensive. I'd not seen generic ones before but it makes sense.
-tony
4985
days inactive
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21 comments
9 participants
participants (9)
-
ajp166＠verizon.net -
arcarlini＠iee.org -
ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
csquared3＠tx.rr.com -
db＠db.net -
mcguire＠neurotica.com -
mtapley＠swri.edu -
robert.jarratt＠ntlworld.com