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In the absence of proper testing
equipment, distortion can become a
problem whose solution requires somewhat
aimless substitution of tubes and
parts until the defective component is
found. With signal-tracing equipment,
the signal can be followed until
the distortion appears. The offending
stage is thus located immediately.
Distortion may occur in almost any tube but usually is confined to the stages working at relatively high levels, such as the detector and audio tubes. A broadcast signal is required when the tracing is done by ear. When an oscilloscope is available a sine wave tone should be used. Although the 'scope locates the stage indisputably, a good ear seldom requires such corroboration. Probable causes of distortion:
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