rca 12bh7

I have two band new UA LA-2A, bought two sets of GE LP 12AX7 pair + RCA 12BH7, that were vintage new and matched and switched the stock LA-2A tubes out.



Was there a difference?

I have never used a 12BH7 before.



Two questions:



1) In Urei LA2 they use a 12BH7 in the output drive section instead of 12AX7(more gain I know) or 12AU7, why is that?



2) Other that the heater current, what is the difference between a 12AU7 and 12BH7?



Thanks!