What is the difference between EL34 A,B,C, or PH tubes.

I'm not 100% on this but I believe the EL34A is a tetrode and the EL34B is a pentode (like standard EL34) The A and B additions are for new Chinese production, possible for EL34 name copyright)
I'd stick with EL34 and EL34B for your BHSE.