AFTER YOU FINISH THE RESTORATION AND PUT IT BACK TOGETHER, CHECK ALL EXPOSED METAL TO BE SURE IT ISN'T HOT. I DON'T CARE IF THE CABINET IS METAL. PLASTIC, WOOD OR BAKELITE. THIS EASY FIX MAY SAVE YOUR BUTT. JUST DO IT.
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| THE "HOT CHASSIS" PROBLEM | ||||||||||||
| IN AN EFFORT TO SAVE MONEY AND TO MAKE SETS LIGHTER, ESPECIALLY PORTABLES, MANY SETS WERE MADE WITHOUT A POWER TRANSFORMER. THE ONLY ADVANTAGE WAS LESS WEIGHT. THE DISADVANTAGES OUTWEIGH THE ADVANTAGES. THE TUBES ARE IN SERIES. THERE IS A VOLTAGE DOUBLER CAPACITOR THAT COULD GO SOUTH ANY TIME. THE WORST PROBLEM IS A HOT CHASSIS. ONE SIDE OF THE AC LINE IS CONNECTED DIRECTLY TO THE CHASSIS. THIS IS A DANGEROUS SITUATION, ESPECIALLY IF YOUR SET USES A METAL CABINET. ALL EXPOSED METAL CAN BE HOT. THIS IS A PROBLEM THAT YOU CANNOT IGNORE. IGNORING THIS PROBLEM COULD MAKE YOU LIABLE FOR INJURY OR DEATH. THE FIX IS VERY SIMPLE. YOUR SET WILL NOT BE HISTORICALLY CORRECT, BUT IT WILL BE SAFE TO TOUCH, PROVIDED YOUR OUTLETS ARE WIRED PROPERLY. THE KEY TO SOLVING THIS PROBLEM IS HOW THE MAIN SWITCH IS WIRED. YOUR SCHEMATIC WILL TELL YOU FOR SURE. ADD A FUSE BETWEEN THE SWITCH AND VOLTAGE DOUBLER. | ||||||||||||
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| I MADE UP SOME SAMPLES OF HOT CHASSIS POWER SUPPLIES. THE FIRST ONE IS THE EASIEST TO SOLVE. THE SAMPLE ABOVE SHOWS ONE OF THE PRONGS ON THE POWER CORD CONNECTION GOING DIRECTLY TO CHASSIS GROUND. USE AN OHMMETER TO SEE WHICH PRONG ON THE LINE CORD GOES TO GROUND. DO THIS WITH THE SET SWITCHED OFF. IF YOU GET CONTINUITY ON ONE SIDE BUT NOT THE OTHER, POLARIZE THE PRONG THAT SHOWS CONTINUITY. MARK IT WITH A MARKER AT THE CHASSIS SO YOU HOOK IT UP RIGHT. IF THIS IS THE CASE, YOU'RE DONE AND THE SET IS SAFE. | ||||||||||||
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| THIS VERSION OF THE HOT CHASSIS IS MORE COMMON. IN THE ABOVE PICTURE, THE SWITCH IS CIRCLED IN RED. EITHER WAY, THE CHASSIS IS HOT. YOU CAN GET BLASTED IF THE SET IS OFF OR ON, DEPENDING ON WHICH WAY IT'S PLUGGED IN. THE FIX IS EASY. IN THE PIC, YOU WILL SEE TWO RED "X'S." ON THE LINE CORD CONNECTION, TRACE AND DISCONNECT THE WIRE THAT GOES TO THE VOLTAGE DOUBLER AND HEATER STRING. TRACE THE WIRES TO THE SWITCH AND DISCONNECT THE ONE THAT GOES TO CHASSIS GROUND. WIRE THE ONE THAT CAME FROM THE SWITCH TO THE VOLTAGE DOUBLER AND HEATER STRING (INDICATED IN BLUE IN THE PICTURE). WIRE THE EMPTY PRONG ON THE LINE CORD CONNECTION TO CHASSIS GROUND. AS BEFORE, DO A CONTINUITY TEST WITH THE LINE CORD AND POLARIZE THE PRONG THAT SHOWS CONTINUITY. WHAT YOU HAVE JUST DONE IS REWIRE THE SET TO MATCH THE FIRST PICTURE ON THE PAGE. AFTER YOU FINISH THE RESTORATION AND PUT IT BACK TOGETHER, CHECK ALL EXPOSED METAL TO BE SURE IT ISN'T HOT. I DON'T CARE IF THE CABINET IS METAL. PLASTIC, WOOD OR BAKELITE. THIS EASY FIX MAY SAVE YOUR BUTT. JUST DO IT. |
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