EI 6HM5. Are these them? http://www.ebay.com/itm/6HM5-6HA5-EC90
Do I need to worry about balance? I see all these " matched " tubes on ebay, but I read somewhere in this thread that that doesn't really mean much.
Those are the ones. And in my opinion, spending extra to purchase "matched pairs" for LD driver tubes is a waste of money. As long as they were made in the same factory at about the same time, they will be fine.