METAL CONE TUBES
MANY MANUFACTURERS USED METAL CONE CRT'S.  THERE WERE SOME ADVANTAGES TO METAL TUBES.  FIRST, THEY ARE LIGHTWEIGHT, THUS REDUCING SHIPPING COSTS.  SECOND, THEY ALLOWED LARGER SCREEN SIZES THAN THEIR GLASS COUNTERPARTS.  IN THE LATE 40'S AND VERY EARLY 50'S, GLASS TECHNOLOGY HAD NOT PROGRESSED MUCH, SO METAL BECAME AN OPTION.  MANY SETS, INCLUDING THREE OF MY RCA SETS, MY ANDREA, AND 21 INCH STEWART-WARNER, USE METAL TUBES.  THE DuMONT ROYAL SOVERIGN (30" DIRECT VIEW) AND THE ROUND 24 INCH SETS USED METAL.

  SAFETY COMES FIRST.  MANY MANUFACTURERS PUT A PLASTIC SHIELD ON THE METAL TUBE, BUT SOME DID NOT.  THE CONE WILL BE CHARGED WITH HIGH VOLTAGE.  YOU DO NOT WANT TO TOUCH IT WHEN THE SET IS RUNNING.  A SHOCK WILL HURT LIKE HELL.  SOME DID ATTACH THE METAL TUBE TO THE CHASSIS (MY ANDREA IS LIKE THIS, WITH PROTECTIVE PLASTIC). 

  IF YOUR SET USES A METAL TUBE, ALL INSULATORS AND THE TUBE ITSELF MUST BE CLEAN.  DIRT CAN CAUSE ARCING AND POSSIBLE BURNTHROUGH.  WHEN REASSEMBLING YOUR SET, ALL INSULATORS MUST BE IN PLACE.  NO PART OF THE CHASSIS CAN CONTACT THE CONE.  YOU CAN'T CONTACT THE CONE UNLESS YOU LIKE PAIN.  IF YOU HAVE A TEST TUBE, USE IT WHILE RESTORING.  AFTER YOUR SET IS RESTORED, YOU WILL NEED TO CHECK THE TUBE PERIODICALLY AND CLEAN OFF ALL DUST THAT HAS ACCUMULATED. 

  THERE ARE DISADVANTAGES TO METAL TUBES.  THE GLASS TO METAL SEALS CAN BREAK DOWN AND CAUSE THE TUBE TO GO TO AIR.  IF YOU CHECK A METAL TUBE AND THE HEATER VAPORIZES, THE TUBE IS FULL OF AIR.  THE METAL TUBE'S FACE IS FLATTER THAN THE GLASS TUBES, SO MECHANICAL MODIFICATIONS MUST BE MADE TO SUBSITIUTE.  YOU CAN USE A GLASS TUBE IN PLACE OF A METAL TUBE, BUT NOT THE OTHER WAY AROUND.  METAL TUBES ARE HARD TO FIND.  REBUILDERS WILL NOT TOUCH THEM.  THE IMPLOSION RISK IS TOO HIGH WHEN REBUILDING.

  IF YOUR METAL TUBE IS GOOD, THEN GO FOR IT.  BE CAREFUL, BUT DON'T BE AFRAID OF IT.  RESPECT IT.  METAL TUBES MAY NOT BE AS BRIGHT AS THEIR GLASS COUSINS.  THE PICTURE ON MY ANDREA IS NICE AND BRIGHT.  METAL TUBES HAVE THEIR UPS AND DOWNS, BUT THEY WILL WORK AS DESIGNED.

  METAL TUBE TYPES INCLUDE, BUT ARE NOT LIMITED TO:
  16AP4
  16GP4
  19AP4
  21AP4 (RECTANGULAR)
  21AXP22 (ROUND COLOR)
THIS IS A 16GP4 METAL CONE CRT.
THE LIP AT THE FRONT OF THE TUBE IS WHERE IT GETS ITS HIGH VOLTAGE.  THE ENTIRE CONE WILL BE HOT DURING OPERATION. 
21AP4.  THIS ONE WAS COMMON IN 21" SETS IN THE EARLY 50'S.  THIS ONE IS PARTICULARLLY HARD TO FIND.
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