Which 6c33c-b tubes for BAT REX monoblocks ?

I am replacing the 6c33c-b tubes in my BAT REX amps.  Does anyone have any opinion on whether to use new production Sovteks or NOS Ulyanov tubes?  Previously, I've  had success with NOS Ulyanov tubes from PartsConnexion.   Until I discovered PartsConnexion, I had problems with the 6c33c-b tripping the fuses in the amps on especially loud passages.  The tubes from PartsConnexion did not have this issue.  Unfortunately, PartsConnexion does not have any stock of the tubes and haven't for months.  Appreciate any thoughts.  Thanks.