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On Tue, 20 Dec 2011 14:55:07 -0800, mike wrote:

stuff snipped

First thing we need to know is what the voltage is at the secondary
of the transformer (which WILL be AC) and if there is anything between
the transformer and the switches (like a rectifier). It is UNLIKELY
there is a rectifier because there is no advantage to using DC on the
bulbs. The #14 bulb is rated at 15 hours at 2.5 volts, and if the
voltage is only 1.5 volts the lights will be dimmer (but the light is
only for "realism" so it does not need to be full brightness) and the
lifespan will be in the hundreds of hours.. This was commonly done in
doll houses and scenery for train sets etc.

From what Jennifer has said, I don't expect we'll be seeing those readings
any time soon. It's really hard to get to those sockets without an adapter
of some sort. The best we can hope for (and it's a pretty good indicator)
is that we can assume the voltage is not too much above 3 volts because the
bulb would glow very dimly if underpowered and very brightly if overpowered.
From what Jen said, it looks about right, if not a little dim. I suspect
the original builder knew that the bulbs needed slight underpowering to last
a longer time.

Generally speeking the operating resistance of a tungsten bulb is
ABOUT10-12 times it's cold resistance - and measuring the cold
resistance of a #14 bulb, other than to determine if it is open or
not, is rather futile.

God, the perfect straight line! RESISTANCE IS FUTILE! (-:

I'm surprised you guys even got her to buy a meter since it's probably not
going to be very helpful. I can imagine how hard it is to position the
probes for this application. That's OK, though. Everyone should own a
meter and know how to use it. I hope she got an audio continuity meter that
beeps when there's continuity. That's all that matters in this case -
knowing that the bulbs have broken filaments. No sense in glazing over a
neophyte's eyes with technotalk. I've done so much tech support I can
"hear" people's eyes glaze over when I am on the phone with them. (-: It's
an art.

It is a nominal .75 watt bulb, with a HOT resistance of roughly 8
ohms, so the cold resistance is closer to 1 ohm than 11 - which is
why measuring the resistance is futile.

Yet another reason to not even try, especially if a consignment of
replacement bulbs is on the way. The wrong ones will burn out very quickly.
I'm betting that since the last bulb she has lights in a few sockets, she
knows all she needs to know about the transformer, especially if it's sealed
in tight (bad design without an access panel).

--
Bobby G.