Question for lighting experts
 

I recently bought a "dial a watt" ballast (250w & 400w) and for some reason, 9 times out of 10 it won't light a new 250w xm 10k bulb.

An old geiseman 10k bulb works fine on it and so does an old 10 xm bulb... The same new 10k bulb works fine on my old balllasts. This is starting to annoy me greatly, an ideas?

My dial a watt ballast lights my XM 250w 14k, I can't imagine the 10k is different??

I've switched the new bulbs around every which way and occasionally it will work but the next day I'm back to square one again. For the last week I gave up and left the geiseman bulb in it and it has been working flawlessly....

is it a screw in bulb? if so, check at the base of the bulb, there is a small wire that comes out where it attaches to the glass, the wire is bent over the base and spot welded to the base, sometimes the spot weld breaks and you get an intermittant connection.

When I change the bulbs around on the ballasts I'm actually changing the ballasts around on the bulbs.
ie: I don't move the bulbs I just plug the ballast into a different reflector so I don't think the bulb is at fault

Next logical step would be to try the suspect bulb in a different socket/reflector. Could still be a bad bulb too though, they're pretty complex inside compared to a standard filament bulb.

ok, so it is the same ballast that won't fire the new bulb but it fires all the old bulbs, and the other ballasts fire the new bulb, is that correct?

if so, have you tried the new bulb in a different pendant?

I have 3 new 10k SE XM bulbs and for ballasts I have an old hamilton hqi ballast, a bluewave 3 hqi ballast and this new dial a watt ballast. Both hqi ballasts will light any of the 3 new bulbs, the dial a watt won't start any of them (most of the time)

I have changed the settings on the dial from normal 250w to the hqi but neither setting will work consistently

if you are swithing the harness and pendant together, I would have to say that you have a bad ballast.
The last thing I would try is a different power source if you haven't tried that.