THERE ARE SEVERAL KINDS OF CRT'S. EARLY ON, MANY MANUFACTURERS USED ELECTROSTATIC TUBES. THESE TUBES HAD FOUR PLATES IN THEM, AND WHEN CHARGED WITH HIGH VOLTAGE, WOULD DEFLECT THE PICTURE. THE 7JP4 IS THE BEST KNOWN. IT WAS USED IN THE MOTOROLA VT-71 AND OTHER SETS OF THE ERA. THIS TUBE IS GETTING VERY HARD TO FIND. SINCE I HAVE NO DESIRE TO HAVE AN ELECTROSTATIC SET, THIS IS NOT AN ISSUE.
MAGNETIC DEFLECTION IS DONE WITH A YOKE MOUNTED TO THE TUBE. THIS IS THE MOST COMMON WAY OF DEFLECTION. MAGNETIC DEFLECTION MADE LARGER SCREEN SIZES POSSIBLE.
FOCUS WAS EITHER DONE ELECTROSTATICALLY (VOLTAGE APPLIED TO A FOCUS GRID) OR MAGNETICALLY (ELECTROMAGNETS OR ACTUAL MAGNETS ON THE TUBE'S NECK). ELECTROSTATIC FOCUS IS THE MOST COMMON.
MANY TUBES USED AN ION TRAP MAGNET. THESE TUBES ARE NOT ALUMINIZED. THE GUN IS BENT INSIDE THE NECK OF THE TUBE, (PIC WILL BE ADDED LATER). THE ELECTRONS ARE WHAT HITS THE SCREEN TO PRODUCE A PICTURE. A BY-PRODUCT IS IONS. THE IONS WOULD BURN THE PHOSPHORS AND RUIN THE TUBE. THE ION TRAP KEPT THE IONS NEAR THE NECK WHILE ALLOWING THE ELECTRONS TO PRODUCE A PICTURE. ION TRAP ADJUSTMENT IS CRITICAL. MOVE THE TRAP ON THE NECK AND WATCH FOR THE BRIGHTEST PICTURE YOU CAN GET.
ALUMANIZED TUBES HAVE A STRAIGHT GUN INSIDE THE NECK. THE MANUFACTURERS PUT A VERY THIN COATING OF ALUMINUM ON THE SCREEN AND BELL OF THE TUBE. AS A RESULT, THE IONS CAN'T BURN THE PHOSPHORS AND THE TUBE IS BRIGHTER THAN ITS NON-ALUMANIZED COUSINS. THE ION TRAP IS NOT NEEDED.
YOU WILL ENCOUNTER MANY TYPES OF TUBES (NOT JUST ROUND AND RECTANGULAR). BACK IN THE DAY, THEY USED GLASS AND METAL TUBES. I WILL DISCUSS METAL TUBES IN ITS OWN SECTION.
MANY TIMES, THE TUBES WERE MOUNTED TO THE CHASSIS. THIS CAN BE AN ADVANTAGE. IF THE RECAP DIDN'T SOLVE THE PROBLEMS, YOU COULD TURN THE CHASSIS ON ITS SIDE AND DEBUG WITH THE TUBE MOUNTED. THIS MAY NOT BE THE BEST WAY TO GO. IF THE TUBE IS CENTERED AND NOT TOO LARGE, YOU COULD DO IT.
TUBES WERE ALSO MOUNTED TO THE CABINET. THIS IS A DISADVANTAGE. UNLESS YOU HAVE A TEST TUBE, GET READY TO POSSIBLY PULL THE CHASSIS MANY TIMES. SAFETY IS A TOP PRIORITY.
MANY PICTURE TUBES ARE GETTING HARD TO FIND. THERE ARE STILL PLENTY OF 12LP4'S OUT THERE. 7JP4'S ARE HARD TO FIND GOOD. THERE WERE SO MANY DIFFERENT CRT'S MADE OVER THE YEARS. I CAN'T REALLY GIVE YOU ANYTHING ACCURATE AS TO WHAT'S AVAILABLE. IT TOOK ME ABOUT 6 MONTHS TO FIND A REPLACEMENT 12LP4 FOR MY 12" PHILCO.
IF YOUR TUBE MOUNTS TO THE CHASSIS, REMOVE IT BEFORE YOU RECAP. PUT IT IN A SAFE PLACE, AWAY FROM KIDS, PETS, ANVILS AND ANYTHING THAT COULD MAKE IT IMPLODE.
MANY TUBES HAVE A BAKELITE BASE THAT CAN COME LOOSE. BE VERY CAREFUL WHEN REMOVING THE SOCKET. SUPERGLUE CAN FIX THIS. MANY TIMES, THE SOLDER CONNECTIONS WEREN'T GREAT. IF YOU SUSPECT A BAD SOLDER JOINT, RESOLDER.
THE HIGH VOLTAGE CONNECTION ALSO VARIES. MOST USE AN ULTOR BUTTON ON THE SIDE OF THE BELL (TOP FOR RECTANGULAR COLOR). SOME HAVE THE HV ON THE SOCKET (9" GE TUBE AND ELECTROSTATIC TUBES). YOU MUST DISCHARGE THE TUBE BEFORE REMOVAL. FOR THE ULTOR TYPE, GET A SCREWDRIVER AND CLIP LEAD. CLIP ONE SIDE TO THE SCREWDRIVER AND THE OTHER TO CHASSIS GROUND. SLIP THE SCREWDRIVER UNDER THE ANODE CAP. YOU MAY GET A HEALTHY ARC. DO THIS MANY TIMES.
I WILL GET INTO MORE SPECIFIC STUFF IN OTHER SECTIONS. THIS IS JUST THE BASICS.