XPost: sci.electronics, sci.electronics.basics, sci.electronics.design   
   From: keinanen@sci.fi   
      
   On Fri, 21 Aug 2009 23:06:08 -0500, "Martin H. Eastburn"   
    wrote:   
      
   >Every one forgets the Cold war.  B-36's and B-52's and such   
   >were all vacuum tubes.  EMP and radiation didn't wipe them out   
   >as semiconductor was.  Transistors were in the 40's post war at   
   >Bell Labs.  Nobel time.   
      
   The EMP became an issue in the 1960's after the nuclear test above the   
   Pacific, so it could not have influenced the much earlier B36/47/52   
   designs.   
      
   Apparently the semiconductor diode reliability was not very good since   
   some early computers had a lot of problems with semiconductor diode   
   reliability.  For instance ENIAC had nearly 18000 tubes but only 7000   
   semiconductor diodes. If I had to design a computer with tubes and   
   diodes today, the amount of diodes would be at least ten times the   
   amount of tubes.   
      
   For microwave receiver applications, if you do not have a good low   
   noise RF amplifier, a point contact diode mixer is a reasonable   
   alternative (often driven by a LO frequency multiplying chain) to get   
   a reasonable system noise figure/temperature.   
      
   Paul   
      
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