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RE: Tube matchin

Posted by Paul Joppa (P) on November 21, 2015 at 09:36:29

In Reply to: RE: Tube matchin posted by neolith on November 21, 2015 at 06:55:42:

Noise is always difficult to measure accurately, because there are so many possible sources which may confound the measurement.

First, the test rig must not contribute significantly if you want the tube noise. That means a quite power supply, and checking the noise from bias and plate load resistances to be sure they are all small relative to the expected noise.

Second, the signal level is small; you need a really quiet amplifier with a gain around 1000 (60dB). This raises the tube noise to a level that can be seen on a measuring device such as an oscilloscope.

Third, you really need a spectrum analyzer, since tube noise has a white noise component plus a "1/f noise" component. The spectrum analyzer is also good for detecting small levels of hum and other interferences, which would otherwise distort or dominate the measurement.

Here's an interesting thread on triode noises:

• thread on diyAudio   (Open in New Window)

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