39225254   
   From: phil_a@tpg.com.au   
      
   "Roger Jones"   
      
   ( snip long story)   
      
      
   ** The EL84 lost vacuum.   
      
   First, at low air density the tube will conduct DC heavily from plate to   
   cathode via ionised air  -  causing a loud hum, accompanied by a purple glow   
   from inside the glass.   
      
   The heater current goes up as heat is now being dissipated into the   
   surrounding air keeping the temp low and hence resistance low.   
      
   As the tube fills with air, there will be no more conduction but the glass   
   will get hot by convection of heat from the cathode.   
      
   If you cannot see any crack in the glass, there may be a loose or corroded   
   pin that let the air in around it.   
      
      
      
   ...  Phil   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)