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.

You can use any type of EL34 !
https://tubedepot.com/products/sino-el34-b-power-vacuum-tube

I did not even know that there are different types of EL 34 tubes.  A good friend brought over to my place various quads of vintage EL 34 and 6CA7 (1950s and 1960s) tubes.  I got to pick out which quad to keep as a gift to use in my BHSE.  I chose a quad of Telefunken tubes.

Best current EL34 variant is the Gold Lion KT77 by a large margin in my opinion and others whose ears I trust.

EL34 (A,B, etc) are power pentodes that can also be run in triode mode