[Kenwood] Checking 3-500 tubes
Dr. Gerald N. Johnson, electrical engineer
[email protected]
2002年6月09日 09:36:40 -0500
About all you can do with the VOM is check for filament continuity and
for lack of grid to filament and grid to plate shorts. There are better
ways to test the tubes than in an amplifier but that's the most common
ham technique.
One can test the tubes for gas but it takes three power supplies and a
couple meters. You put +45 on the control grid, -45 on the plate, and an
adjustable filament supply. You bring up the filament heat until the
control grid current is about the rated grid current, then you monitor
the plate current. It should be microamps or smaller. The fraction that
the plate current is of the grid current is a nearly direct measure of
the gas in the tube. Its applying the tube like an vacuum gauge. Such a
gas check will test better if the tubes have been run with filaments
alone for a day or two to allow the gettering deposit to work. That
simmering is good for any power tubes because the seals do leak.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson. Reproduction by
permission only.