Yea, progress! The load of some tubes changes between spot, tune and operate. That is normal. If I set my 813 rig up for 32ma grid drive (no B+) then in transmit its often 25 or so ma. Its best to have PLENTY of grid drive ability. I have an exciter that has a 6146 at 600 volts or more and it will not drive three 4-400's enough for plate modulation but does ok in screen modulation. Its good for a pair of 4-125's. To drive a pair of 4-400 tubes deep into class C with a lot of grid leak bias, you want more then one 6146 will do I would think. Tetrodes modulate best when driven well into class C, increasing the grid leak resistor increases the bias voltage and increases the drive requirements. I think the 813 rig (2) takes 20 watts of drive to give 32 ma and -350 volts bias.