Halogen lamps will give about 20% more light than evacuated air lamps. The
tungsten filament will burn brighter and longer for the same voltage because
the halogen does not allow the filament to "oxidize" as quickly. But
remember it is possible to find 12V lamps rated for 10000 hours (long time!)
from Mouser electronics (mouser.com), and others.
Heck if I have to replace any instrument lamps, I will look at the new
ultrabrite white LED's, available from Digikey and Mouser. They are rated at
10 to 100 times the life of an incandescent (probably longer than I will
live). They drop about 5V and require about 20 ma, so you will need a
resistor in series, probably about (14V-5V)/20ma = 450 ohms. The reostat can
be wired in series for dimming. If you really want to light up the panel put
a couple of these in each spot, but you might think you are seeing UFO's if
you drive a lot in the country!!
Tim Economu
'69 BGT mona
-----Original Message-----
From: Paul Hunt <paul.hunt1@virgin.net>
To: Arnold Molloy <a.j.molloy@worldnet.att.net>; Tim Economu
<economu@whidbey.com>
Cc: MG List <mgs@autox.team.net>; mgbob@juno.com <mgbob@juno.com>
Date: Tuesday, November 09, 1999 10:58 AM
Subject: Re: Halogen dash lights
>Your right, and that maintained a constant voltage to the load over a range
>of input voltages and load currents. However a series zener with a
>relatively constant supply voltage (14.3v when running, remember, not 12v)
>and a relatively fixed load (n * lamps) will still give a relatively fixed
>voltage across the load e.g. 14.3 - 5.1 = 9.2.
>
>Auto bulbs may well be labelled '12v' but they are in fact rated at 14v.
>Which is why non-auto 12v bulbs give a brighter light than auto 12v bulbs,
>but they will also suffer from a shortened life, greatly shortened as users
>of 7.5v non-auto lamps have found, and also draw double the current of a
set
>of auto bulbs shortening the life of the, very expensive, rheostat.
>
>I can't really see the point of putting lower voltage, same wattage lamp in
>and then having to drop the voltage. For a similar technology bulb isn't
>the end result the same? Can't speak for halogen instrument lamps as
>Halford's don't seem to stock them. But if the theory is that that give
>more light and less heat for the same electrical power then they really
>should be an improvement.
>
>Beats me why anyone should need to read the numbers anyway. They're
>analogue instruments, can't you tell what's happening by the angle of the
>needle? Do you all have watches with numbers round the outside so you can
>tell what time it is?
>
>But then, I'm just an old fart who bought two new rheostats for his two
cars
>and has never had them off max. I'd also need a set of arc lamps to be
able
>to focus on the figures at night anyway.
>
>PaulH.
>
>-----Original Message-----
>From: Arnold Molloy <a.j.molloy@worldnet.att.net>
>To: Tim Economu <economu@whidbey.com>
>Cc: MG List <mgs@autox.team.net>; mgbob@juno.com <mgbob@juno.com>
>Date: 09 November 1999 02:02
>Subject: Re: Halogen dash lights
>
>
>>Tim;
>>Maybe modern electronics is similar to modern math????? But back in the
>50's
>>when I went to school a series resistor was used to drop the excess
>voltage,
>>(5-6V) and the zener (in this case 7.5V) was placed across the load
>(parallel)
>>to determine the voltage applied. IMHO
>>
>>Arnie Molloy 53 TD
>>
>>
>>Tim Economu wrote:
>>
>>> Dear Bob, Jay, et al:
>>>
>>> If you want to use your 7.5V bulbs and have them last a long life, just
>add
>>> a 5.1V zener diode in series with the bulb to drop the other few volts.
>The
>>> bulbs will last the normal 2000 operating hours (their rating) and you
>will
>>> still get a nice bright bulb. The zener can also be purchased at Radio
>>> Schlock (misspelling on purpose!) and will be soldered into the circuit
>with
>>> the band end (cathode) toward the plus side of the battery on neg ground
>>> systems.
>>>
>>> But really, isn't the dim instrument good for all of us? And some LBC's
>have
>>> REOSTATS!! Wow modern technology!!
>>>
>>> Kind regards,
>>>
>>> Tim Economu
>>> '69 BGT mona
>>> email: economu@whidbey.com
>>>
>>> > It was previously said....
>>>
>>> Date: Sun, 7 Nov 1999 17:34:24 -0500
>>> From: Bob Howard <mgbob@juno.com>
>>> Subject: Re: Halogen dash lights
>>>
>>> Jay,
>>> I was one of the guys who contributed to the Radio Shack bulb
>>> correspondence.
>>> Experimentation with the 7.5 volt bulb (#50) demonstrated great
>>> illumination, so bright that the rheostat could be turned down almost to
>>> the miniumum
>>
>
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