Tubes Asylum

RE: Tube testers are not exact as tubes are not exact. . .

199.82.243.71

In Reply to: RE: Tube testers are not exact as tubes are not exact. . . posted by John PA on May 11, 2008 at 20:09:22

Exactly, it depends on how the parameters that are fed to the tube. If you can accurately set the plate voltage, the signal AC voltage, the screen voltage, and current draw and then measure the Gm you can get pretty consistent measurements. A lot of tube testers do not run the tubes anywhere near the same voltages and currents as they see in a circuit. Most tube testers also do not give you direct control over all of the voltage and current parameters as well.

Measurements only are valid if you state the results and the actual test conditions at each pin for how the results were generated. The results are then only vaild for that particular set of conditions. Then of course the perfectly measuring tube is microphonic and noisy which makes it useless.

Also, a measurement is only for the tubes ability to amplify or not to draw too much current. A high measuring tube versus a midrange measuring tube is not an indication of quaility of one over the other, it just indicates that it works and has life left.
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Long Live Dr.Gizmo

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