I figured it out. Looks like 400 volts.
According to my Groove Tubes bias kit manual, that means 20-50 mV is the range, with a nominal set point of 37.5 mA for El34's.
6l6's are 25 to 60, with a set point of 45 mA.
If PRS recommends 30 mA for 6l6's, their recommendation for El34's must be...