Rich said: >AB2 grid-driven makes rotten splatter with 4-400s. Not necesarily. But you do need a well regulated screen supply, a 'stiff' bias supply that doesn't move with grid current (mine moves under 50millivolts), some RF NFB in the filament circuit, and about 3600volts on the plates. Pappenfus explains why AB2 can be more linear than AB1. 73 Peter G3RZP