In article ,
"Mark Jones" 127.0.0.1 wrote:

Bob wrote:
Looking for tiny incandescent lamps for my TM-451A Kenwood.

Apparently these are 6 V or so; there are four of them in
series parallel controlled by a regulator to vary intensity.
They light up the LCD and two of them are burned out.

I have searched many of the usual sources and can't seem to
locate replacement lamps; as a last resort I could go to
Pacific Parts but they are so expensive. These are just
inexpensively made tiny bulbs with wire leads.

Any suggestions?

Bob

Perhaps one of these might fit the bill, LED replacements for typical
incandesents...

http://dkc3.digikey.com/PDF/T033/1200.pdf


You seem fixated on replacing the originals with incadescent bulbs. Here
is another source: http://www.lightbulbwarehouse.com/

And if that is too expensive, try the miniature bulbs used for model
trains or doll houses or christmas tree lights.

Al

--
There's never enough time to do it right the first time.......

William Sommerwerck wrote:


He didn't say where he got the 12th-power rule. Anybody know?

I don't know where it came from, or if it is accurate.
(I don't doubt or dispute it - I just don't know.)
But in 1978 I wired the 2 bulbs in the each of the EXIT
lights in the church in series. They were burning out in
3-4 months before that. Since I wired them in series, we
haven't had to replace a single bulb. The bulbs are lit
24x7, so they don't go through any on/off stress.

On Thu, 28 Aug 2003 12:44:54 -0700, the renowned "William Sommerwerck"
wrote:

Thanks for the confirmation of 12th power.

The 12th power approximation does originate at GE Lighting, AFAIK, but
is only valid for voltages rather close to the rated operating
voltage, and for typical high voltage incandescent lamps. Long-life
and halogen bulbs WON'T behave the same.

http://www.eaoswitch.com/about/lamps.htm

Here's a rule of thumb for low-voltage halogens:

http://www.ndlight.com.au/low_voltage_lighting.htm

They claim a 5% voltage increase will reduce life by 50%, which is
more like the 13.5th power.

The one time I checked the 12th power approximation against actual
testing of low wattage high voltage (mains) lamps it was off by more
than an order of magnitude, so take the whole thing with a grain of
salt, IMHO, unless your lamp type matches the type used for testing.
I'm sure a real lamp specialist could go on for hours about this sort
of thing.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

The 12th power approximation does originate at GE Lighting,
AFAIK, but is only valid for voltages rather close to the rated
operating voltage, and for typical high voltage incandescent
lamps. Long-life and halogen bulbs WON'T behave the same.

The urban legend about halogen lamps is that reducing the voltage even slightly
causes the filament to burn out prematurely. The reasoning is that the slight
drop in temperature reduces the halogen self-healing effect much more than it
reduces the evaporation of the filament. I believe this is correct.

Thanks for the references.

Now... Does anyone know anything about helium reducing the life of incandescent
lamps? grin


http://www.eaoswitch.com/about/lamps.htm

Here's a rule of thumb for low-voltage halogens:

http://www.ndlight.com.au/low_voltage_lighting.htm

They claim a 5% voltage increase will reduce life by 50%, which is
more like the 13.5th power.

The one time I checked the 12th power approximation against actual
testing of low wattage high voltage (mains) lamps it was off by more
than an order of magnitude, so take the whole thing with a grain of
salt, IMHO, unless your lamp type matches the type used for testing.
I'm sure a real lamp specialist could go on for hours about this sort
of thing.

On Sun, 31 Aug 2003 10:38:58 GMT, Spehro Pefhany
wrote:

On Thu, 28 Aug 2003 12:44:54 -0700, the renowned "William Sommerwerck"
wrote:

Thanks for the confirmation of 12th power.

The 12th power approximation does originate at GE Lighting, AFAIK, but
is only valid for voltages rather close to the rated operating
voltage, and for typical high voltage incandescent lamps. Long-life
and halogen bulbs WON'T behave the same.

http://www.eaoswitch.com/about/lamps.htm

Here's a rule of thumb for low-voltage halogens:

http://www.ndlight.com.au/low_voltage_lighting.htm


The problem with Halogens is LOW voltage reduces the life of the bulb
as well. The Halogen Cycle requires a minimum temperature in order to
re-deposit the tungsten on the filament.Low voltage boils the tungsten
off and deposits it on the glass envelope. Eventually the glass gets
dark and the filament gets too thin and burns out. Specified voltage
maintains proper temperature for thr reddepositing of tungsten on the
filament.
This operating heat is why quartz glass envelopes are generally used
for halogen bulbs.
This is copied from elsewhere on the web:

What is the difference between the internal conditions and mass
transports happening inside the noble gas fill, and the halogen
cycle incandescent bulbs?

Noble gases do not react with the tungsten vapor, leading to a layer
of semi-opaque condensed tungsten on the inner surface of the
bulb. Since the bulb is cooler than the boiling point of tungsten,
tungsten is gradually transfered from the filament to the bulb until
the filament burns out.

Halogens react with tungsten vapor, resulting in a layer of tungsten
halide on the inner surface of the bulb --- but since tungsten
halide is transparent, less light is absorbed. Also, tungsten halide
has a low enough boiling point that it can re-evaporate when the
bulb is hot enough. Finally, if tungsten halide molecules get close
enough to the fillament, they can disassociate back into tungsten
and halogen atoms, and the tungsten can be re-deposited onto the
filament, extending its lifetime, while the halogen goes back into
the fill gas.

There is an important elegance to the tungsten-halogen cycle. Because
the filament is a series resistance with a positive temperature
coefficient of resistance, any part that thins by sublimation runs
hotter than the rest. In a conventional bulb the heavy gas fill acts
to reduce sublimation and thermally insulate the filament so a given
power level gives more visible light. However, a localized thinning
gives positive feedback and failure.

In a tungsten-halogen bulb, sublimated tungsten reacts to give
volatile tungsten halides that thermally decompose and redeposit metal
at the hottest spots. The bulb does not darken from transported
tungsten. The hottest spots get rebuilt. Negative feedback allows a
filament to be run very hot indeed.

There is a price to be paid. The envelope must be made of fused
silica to take the high temperature. A mere trace of sodium (a
fingerprint) catalyzes crystallization of fused slica to cristobalite
at temp. When the envelope cools or heats it cracks from differential
coefficients of thermal expansion. When tungsten halogen bulbs fail
in use the results are often quite... attention-getting. Internal
pressure at operating temperature can be several atmospheres.
Tungsten halogen bulbs also have a pretty good UV component compared
to ordinary incandescents unless the envelope is doped with cerium or
such.

In wrote:

But in 1978 I wired the 2 bulbs in the each of the EXIT
lights in the church in series.

Congratulations, you probably bypassed a safety feature. If they're in
parallel, if one burns out the other keeps going. In series, if one
goes they're both out, and the exit sign is no longer visible.

nobody wrote:

In wrote:


But in 1978 I wired the 2 bulbs in the each of the EXIT
lights in the church in series.


Congratulations, you probably bypassed a safety feature. If they're in
parallel, if one burns out the other keeps going. In series, if one
goes they're both out, and the exit sign is no longer visible.

But if he'd have left them in parallel, they most certainly would have
both burned out long ago! :-p

Cheers,
Fred
--
+--------------------------------------------+
| Music: http://www3.telus.net/dogstarmusic/ |
| Projects: http://dogstar.dantimax.dk |
+--------------------------------------------+

A diode, ballast, or capacitor in series with each lamp would be
fairly good too. Ballast is best because it performs surge
suppression.

Stepan

On Tue, 02 Sep 2003 21:04:55 GMT, Fred Nachbaur
wrote:



nobody wrote:

In wrote:


But in 1978 I wired the 2 bulbs in the each of the EXIT
lights in the church in series.


Congratulations, you probably bypassed a safety feature. If they're in
parallel, if one burns out the other keeps going. In series, if one
goes they're both out, and the exit sign is no longer visible.

But if he'd have left them in parallel, they most certainly would have
both burned out long ago! :-p

Cheers,
Fred

On 2 Sep 2003 20:44:40 GMT, nobody wrote:

In wrote:

But in 1978 I wired the 2 bulbs in the each of the EXIT
lights in the church in series.

Congratulations, you probably bypassed a safety feature. If they're in
parallel, if one burns out the other keeps going. In series, if one
goes they're both out, and the exit sign is no longer visible.

And what if both burn out in parallel, which they eventually will -
and eventually is measured in months or, at best a low number of
years.
With the series string, if one blows it will likely be a decade or 2
or 3.

In article , Stepan
Novotill wrote:

A diode, ballast, or capacitor in series with each lamp would be

That would have been the proper solution. There are these little
buttons you stick to the tip of the screw-base of the bulb.

You then screw this entire thing into the socket. It's called a "bulb
saver" and is essentially a tiny diode in series that chops the
voltage across the bulb in half.

I assume the bulb bases for these exit lights are much smaller than
Edison based household bulbs (intermediate base perhaps?) and the
bulb savers I've seen are only for Edison sockets.

I think some EXIT lamp manufacturers were also selling LED retrofit
kits for some of these lights.

Also, door slamming and vibration could have been a partial reason for
premature lamp failure.

But now we're getting WAAYYYYYY off topic here.

--
Sven Weil
New York City, U.S.A.