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There's the old tried-and-true "thonk test" for a rubbing voice coil. You unmount the speaker, hold it up by the rim, and thump it smartly on the back of the magnet with the ball of the other hand. The cone should emit a clear, resonant "thonk!". Any trace of fuzziness indicates rubbing.
One caveat - if the output xfmr is mounted on the speaker, be sure to disconnect one side of the vc from the secondary. Otherwise the loading will prevent a clear thonk.
Last edited by old_coot88; 03-23-2014 at 08:46 PM.
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