On Tue, 12 Jul 2011 12:03:40 -0400, The Revd
wrote:

I assumed that a 12V halogen bulb would take DC voltage. Am I wrong?
The lamp stopped working, the bulb is OK (continuity fine, at least).

They intentionally run on DC. This article explains some of it:
http://www.radiolocman.com/shem/schematics.html?di=28080
http://www.rlocman.ru/i/File/2007/05/07/EL_transf_12V.pdf
Quoting:
The "electronic" transformer represents an alternative means of
power conversion to the more standard iron core, 50 Hz transformer
technique. The advantages of the electronic transformer compared
with the classical solution a
- The output power from the electronic transformer to the
lamp can be varied, thus dimming control can be added;
- It is possible to include protection against short
circuit of the lamp filament;
- Weight can be reduced and the construction made more compact;
- Acoustic noise (mains hum) is eliminated.

In addition, if you've ever watched an AC driven light bulb filament
on a high speed camera, the filament vibrates slightly at 60Hz. This
is not a problem when the filament is fairly thin, flexible, and cool.
However, doing the same at the higher temperatures of a halogen bulb
will vibrate the stiff filament until it breaks.

DC rules. Edison was right and Tesla was wrong.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558