b7a28685   
   From: apogosso@tpg.com.au   
      
   > Alex:   
   > The only way the current n the screen grid can reverse is the secondary   
   > emission from the screen grid. For this to happen, the tube shall be a   
   > tetrode with Vp>Vg2 or a pentode with Vg3 > Vg2. If g2 has a pronounced   
   > and   
   > consistent secondary emission, then Vg2 voltage will tend to rise (jump   
   > because of the diodes) to about 20...50V below the plate (tetrode case) or   
   > below g3 (which is nearly connected to plate in these odd circuits). Thus   
   > g2   
   > will be tracking plate with no g2 net current!!!!!   
   >   
   > However I do not think one can dependably rely or reliably depend on the   
   > secondary emission from g2.   
   >   
   > And of course, if the beamformer plates or g3 is connected to the cathode,   
   > this will not work at all. And majority of the output tubes do have g3 or   
   > beamformers connected to cathode.   
      
   P. Turner:   
   I cannot observing evidence of g2 secondary emissions.   
      
   Patrick Turner.   
      
   Alex:   
   Which power tetrode did you use for the experiment? Or which pentode with g3   
   connected to plate? ( I do not have a tetrode to experiment.)  Note that   
   there will be no secondary emission current in a conventional pentode or   
   beam tetrode with g3 or beamformer connected to cathode, so EL84 or 6V6 will   
   not exhibit any secondary emission from g2.   
      
   Generally I would think that secondary emission from g2 is possible (as from   
   the plate) but it is not consistent enough to build a circuit around it.   
      
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