pucho812
Well-known member
Um blueish glow is caused by one of 2 things.
) Most Svetlana glass power tubes show FLUORESCENCE GLOW. This is a very deep blue color. It can appear wherever the electrons from the cathode can strike a solid object. It is caused by minor impurities, such as cobalt, in the object. The fast-moving electrons strike the impurity molecules, excite them, and produce photons of light of a characteristic color. This is usually observed on the interior of the plate, on the surface of the mica spacers, or on the inside of the glass envelope. THIS GLOW IS HARMLESS. It is normal and does not indicate a tube failure. Enjoy it. Many people feel it improves the appearance of the tube while in operation.
2) Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.
So you might have a leak. AS for the rattle it could be filiment rattle.
If a tube rings like a telephone it suffers from "filament rattle." Like a microphonic tube it should be replaced. Filament rattle isn't technically the same since the tube isn't acting like a microphone. Often you'll hear people mistakenly identify filament rattle as microphonics.
AS for testing caps yeah you will get an accurate reading with the cap out of circuit as you would a resistor you could get away with only one leg out as opposed to removing the cap all together however thats usually a pain so you would have to pull it out.
I ahve measured caps in the circuit and usually get enough of a close enough reading to go o.k. not really an issue.
) Most Svetlana glass power tubes show FLUORESCENCE GLOW. This is a very deep blue color. It can appear wherever the electrons from the cathode can strike a solid object. It is caused by minor impurities, such as cobalt, in the object. The fast-moving electrons strike the impurity molecules, excite them, and produce photons of light of a characteristic color. This is usually observed on the interior of the plate, on the surface of the mica spacers, or on the inside of the glass envelope. THIS GLOW IS HARMLESS. It is normal and does not indicate a tube failure. Enjoy it. Many people feel it improves the appearance of the tube while in operation.
2) Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.
So you might have a leak. AS for the rattle it could be filiment rattle.
If a tube rings like a telephone it suffers from "filament rattle." Like a microphonic tube it should be replaced. Filament rattle isn't technically the same since the tube isn't acting like a microphone. Often you'll hear people mistakenly identify filament rattle as microphonics.
AS for testing caps yeah you will get an accurate reading with the cap out of circuit as you would a resistor you could get away with only one leg out as opposed to removing the cap all together however thats usually a pain so you would have to pull it out.
I ahve measured caps in the circuit and usually get enough of a close enough reading to go o.k. not really an issue.
