Hi, All ! I am going to build an amplifier using GU-46 tube. It is glass pentode. You know in the tetrodes we need to use a shunt regulator to cure the negative screen current problem. But is it safe to use a series type regulator for pentodes ? I.e. can the screen current be negative (at first sight it can't)? All the best, Oleg 73 de UR3IQO