which EL 34 for VTL 225s?

EH tubz are less durable and need replacements more freequent so there's no savings there.
Teslas are much more durable but bass is much thinner than with EH.
Svetlanas are excellent tubes on durability, acceptable bass and great midrange.
EI34 fatboys combine all of EH and Svetlanas positives thus I do recommend them.

I just sold my 225's. I used Electro-Harmonix EL34's with great success. They are reasonably priced.
I don't know why Tesla's would have a problem, but, from time to time, I did have a tube fail or a fuse would blow.
Should I assume your friend is biasing the amps properly? Was it one tube failure, or all?
By the way, I didn't sell them because I didn't like them. They are terrific amps.