I replaced a grain-of-wheat lightbulb for a clock-radio dial with one from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

Many years ago, when transistor amplifiers were still new and exotic, Allied
introduced the KG-870, an integrated amp using germanium alloy transistors (you
know, the ones that barely got past 5kHz).

At that time, a lot of attention was paid to protecting the output devices.
(Germanium transistors were prone to thermal runaway.) Allied had an interesting
solution -- the emitter resistors were actually 12V automotive lamps! If "too
much" current passed through the transistor, the bulb's resistance would
increase, restraining the flow.

The bulb was also supposed to be a fuse. The writer of the Electronics World
article explained that the life of a tungsten lamp varied as the 12th power of
the applied voltage. Get the voltage high enough, and the lifetime becomes a
fraction of a second.

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

In article ,
mentioned...
I replaced a grain-of-wheat lightbulb for a clock-radio dial with one from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

[snip]

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

Well, the GE mini lamp catalog mentions this, and GE has been around
since day 1, so I would guess that they came up with the figure.


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Don't be ripped off by the big book dealers. Go to the URL
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"William Sommerwerck" wrote in message
...
I replaced a grain-of-wheat lightbulb for a clock-radio dial with one
from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

Many years ago, when transistor amplifiers were still new and exotic,
Allied
introduced the KG-870, an integrated amp using germanium alloy transistors
(you
know, the ones that barely got past 5kHz).

At that time, a lot of attention was paid to protecting the output
devices.
(Germanium transistors were prone to thermal runaway.) Allied had an
interesting
solution -- the emitter resistors were actually 12V automotive lamps! If
"too
much" current passed through the transistor, the bulb's resistance would
increase, restraining the flow.

The bulb was also supposed to be a fuse. The writer of the Electronics
World
article explained that the life of a tungsten lamp varied as the 12th
power of
the applied voltage. Get the voltage high enough, and the lifetime becomes
a
fraction of a second.

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


Lamps and PTC thermisters are used as non-linear resistors. The diode knee
is also very non-linear. Lamps are sometimes used in the feedback loop or
good clean sine wave oscillators. They stabilize around the non-linearity.
Ghost

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.

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

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.

On Wed, 03 Sep 2003 02:28:32 GMT, the renowned (Sven
Franklyn Weil) wrote:

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.
snip

The RMS voltage across the bulb is reduced by ~29%.

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

In article ,
mentioned...


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


I gotta tell you what happened at work last week. The head of
security came over and told us that someone had complained that one of
our tables was blocking the door (it's a temporary setup). The head
of registration told him that she put it there to keep the students
from leaving. The security guy says, but that's an emergency exit,
see that sign up there?

So she says, oh, ok. Well, then, can we move the sign?

:-)))


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 at hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@