Couldn't tell you. That's the problem, I don't normally work on neon nearly all the service we do is florescent or led. On internally lit signs, we usually just pull old neon, and replace it with led's. I've only ever repaired neon twice and don't really know any specifics of it. other than basic troubleshooting.
It's a shame everybody's moved to more cost effective lighting, I love the look of exposed neon, nothing else really compares.
"Yesterday, upon the stair,
I met a man who wasn't there.
He wasn't there again today,
I wish, I wish he'd go away..."