90e18133   
   From: apogosso@tpg.com.au   
      
   "Patrick Turner"  wrote in message   
   news:e8dcd550-1d20-453c-a98d-f76f8dc26c5a@z11g2000yqz.googlegroups.com...   
    It seemed to me the screen current was always only in   
   ONE direction, ie, electrons flowing into the positive screen supply   
   as is does at the anode. Conventional current flow is from positive to   
   negtive. A series diode in the anode circuit pointing into the anode   
   allows flow. allows  averlam   
   So the diodes placed the way they are shown for g2 would just allow   
   screen current all the time in one direction and I cannot think why it   
   would want to flow the other way.   
      
   I'm very suspicious of the validity of the claims at that oestex site.   
      
   Patrick Turner.   
      
   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.   
      
      
      
      
      
      
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