MH's won't fire for more than a minute

[adhoc]

I just bought 2 new 10K 175W Ushio bulbs. I am trying to fire them with Advance ballasts, but can't do so with any regularity. They will fire for about a minute, and then tend to shut down.
I tried swapping bulbs around, rewiring the ballasts, plugging into another circuit, but no luck. I was able to fire one bulb on either of the ballasts after trying it 2 or 3 times (not sure how reliably it's going to fire on first try). The other bulb wouldn't fire for more than a minute or so. It glows steady, not even flickering when it first fires, gradually gets brighter and then -off-. Almost bright enough that I can't look at it directly before it shuts down.
I'm just about out of ideas now. Any suggestions? Anything else I can test?
Edit - I did some searching prior to posting and I saw other people had similar problems, but I didn't really see any resolution?

 

[adhoc]

OK, well through nothing but persistence I was able to get both bulbs to stay lit. Haven't tried shutting down, cooling off, and re-firing yet. Is my experience typical?

 

[saltfan]

I don't know how old your ballast is but that is the reason you are having trouble firing the bulb off. The ballast is going out. And the light going really bright, brigher than it should be, is another indicator.