What 6h30's have you used so far? Unfortunately, there are not a lot of variations out there to choose from.
At the top of the list are the 6h30dr's which at this point for me are cost prohibitive(between $300-$350pr.)then you have sovtek and electro harmonix. All are Russian made.
As and alternative, I've found that the electro harmonix 6h30pi gold's are pretty good(I can live with them) compared to the 6h30dr's particularly when you consider price. I would stay from the sovteks, they're just not that good.
Electro harmonix is currently Audio Research's stock tube which says a little something about their quality.