[BC] the Purple tube...

[Lewis Munn]

I found this string interesting.  Anybody wanting to toss out older regulators and thyratrons, let me at your waste baskets!!
   
  I recall hearing that some of the old 327 detector tubes were delibrately made slightly gassy, as it improved their sensitivity.  The gas added electrons to the flow by controlled ionization so there was more amplification in them.  Kept the plate volts low so the electron multiplication was not a runaway avalanch.  Did not want to put them in in audio applications at the normal higher plate voltage or they would arc internally.  They had blue glass envelopes to avoid photoelectric effects.
   
  I recall an old WE limiter, using I think a BH as a voltage reference and a BR as the rectifier...both as I recall cold cathode tubes.  Type 83 tubes were around a long time...mercury vapor rectifiers...low internal drop.  just had to keep the condensed-mercury temperature within in range or the tube would either arc or would overheat from high internal losses.  And who could forget the old car radios with the vibrator power supplies, and an 0Z4 as the rectifier.  Pretty purple in operation as I recall.  Cold cathode full wave rectifier.
   
  A lot of military stuff used the 3B28 Xenon rectifier...low loss, high current capability,and not temperature sensitive as the mercury vapor rectifiers were.  And a very pretty glow in operation.
   
  We still in some applications use Ignitrons for very high voltage high current controls.
   
  And thyratrons are still used for high-voltage high current switching.  
   
  My favorite tube tho is the HY-5.  Hydrogen thyratron, used in research and huge radars. I don't think that they yet have SCR banks that can be afforded to switch 40,000 volts at 40,000 amperes!  I would love to see a HY-5 in full bore operation. I understand it sounds like a high-calibre gun firing, and the ionization is so intense you can see the red Balmer spectral lines thru the thick ceramic envelope...down in the very deep red.
   
  My favorite single gas is krypton, with a lovely violet glow.
   
  Oh, and gas discharge tubes are still used...neon signs, sodium vapor lighting, mercury vapor lights, crater tubes for the generation of reference wavelengths, etc.
  They may be "soft", but they carry workhorse loads.  And in many cases they are self-healing after overloads.
   
  And finally, a few of the older limiters and modulation monitors I know of used NE32 or similar lamps as a voltage reference tubes, and 885 or 2D21 thyratrons to handle the overmodulation or peak indicators.  I used many of the CP Clare gas-filled surge supressor arc tubes in lightning supression service.
   
  I know solid state is more efficient, if somewhat more fragile, but, I LIKED the blue glow of the 8008's, 6 of them in a three-phase plate supply.  And being able to spot a potential failure when the tube's blue started to turn green around the gills.
   
  HUZZAH for the soft tubes, and their kin...long may they glow.
   
  Looey Munn
  Roundup, MT
  
 

		
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