Space Charge tubes

Bob Bruhns bbruhns at
Fri Sep 9 09:11:17 CDT 2005

Interesting tubes.  Designers were trying to coax more emission out of the cathodes so they could get some current at the super-low plate voltage.

I encountered space charge tubes for the first time while I was scanning and proofing the AM Press/Exchange issue cited in the article.  The signal appeared to go to the screen grid, and a fixed positive bias was applied to the control grid, and I thought there was an error in the schematic.  People bungle that stuff all the time.  I had to look it up and read about it before I believed it.  But that's how it was really done.

People do interesting things with tube grids.  Grounded-grid 813s are a good example. The 813 was designed to be a beam power tetrode (an advanced design from the 1930s), but if you simply tie the grids together, the tube becomes a zero-bias triode.  The 813 was never intended to work that way, but it does.  It goes to show that tubes were a natural - the technology really *wanted* to work.  The development of advanced cathode designs, advanced grid structures, and advanced plate materials and coatings, and magnetrons, traveling wave tubes, beam-deflection multipliers, etc, is a tribute to the genius of that era.

----- Original Message ----- 
  From: Andre Kesteloot 
  To: AMRAD Tacos 
  Sent: Friday, September 09, 2005 9:08 AM
  Subject: Space Charge tubes

  André  N4ICK


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