The manual for my Randall RM100 says the range for EL34's is 30mV to 38 mV.
It's subtly implied that I shouldn't run them lower than 30mV. The tubes came matched at 25.1mV so I'm just trying to pop them in and check it'll work before I track down a multimeter so I can bias them
in general biasing lower than suggested makes the amp sound worse than it should, and since the circuitry is designed for the recommended bias range It might cause other problems. Stay in the range.