|
Rich Measures (SK) wrote about this, and suggested (for different tubes) a possible way to fix it by swinging a live tube around your head.? I guess if you do it outdoors and the tube is already shorted, then no harm, no foul, right? ? Tom Rauchen Verboten?W8JI has more to say.? Locate his web site and read to your heart's content -- after Measures passed, Tom corrected all of his own errors and added a whole lot of new, better info. Basically, this is usually caused by the grid not being concentric with the cathode / heater.? When the tube gets hot, the grid softens at red heat and falls into the cathode, thus shorting it.? When the grid cools, it welds itself to the cathode and the tube is toast forever.? Unless, of course, you want to try exciting the cathode and swinging the tube around your head once it gets good and hot. ? This must have worked at least once, or else Measures wouldn't have published it.? For my part, I don't think it's a very good idea, because it's a red-hot lump of metal encased in glass, and my back yard is full of vintage sports cars and antenna structures.? And dry brush.? It hasn't rained here all summer and it's only a matter of time before everybody in the city?burns down their back yard. If you don't mind burning down your basement, you might put an ohmmeter between the grid and cathode to confirm the short, and then get the cathode hot.? By bumping the tube with some force against a padded surface and giving it 1/8 of a turn each time, you MIGHT knock loose?the weld,?as shown by the ohmmeter indicating an open circuit. Or you might try the anti-barnacle trick, which is to put a high-voltage, high-current charge across the grid and cathode, and evaporate the weld.? Whatever you do, keep in mind that this tube is dead and is good for nothing more than a night light now. ? So have fun, be safe, and you might get lucky enough to break loose the weld and have a usable tube again.? But don't bet the farm on it. 73 Jim N6OTQ? On Fri, Sep 8, 2023 at 9:21?AM Bob <W4JFABob@...> wrote:
|
