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Tube vibration

Posted by Al Sekela (A) on January 23, 2007 at 11:06:28

In Reply to: Great many thanks posted by zuheyr on January 22, 2007 at 23:54:15:

Vacuum tubes have very thin and stiff internal elements that are minimally supported. The glass envelopes can ring like bells, and the internal elements can also ring. This makes support of tube gear a challenge, as any vibration from the speakers that gets into the chassis can set up resonant vibrations inside the tubes.

Tubes with defective internal supports (usually caused by warping of some of the elements) are called "microphonic." You can hear the thump in the speakers when tapping on such tubes. However, all tubes are microphonic to some degree, and this affects sound-stage performance.

Since, as a practical matter, we cannot directly damp the tube elements against vibration, improving sound-stage and resolution performance of tube gear is a matter of judicious damping and isolation applied to the external envelopes and supporting chassis parts. Use care to not block the heat dissipation from the envelopes, especially for power tubes. Also, be aware of the high voltages present and do not use materials that will break down under voltage stress.

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