Signs of Detector Overloading

Radio Record, Volume VIII, Issue 25, 28 December 1934, Page 43

Signs of Detector Overloading

MANY sets, unknown to their owners, are operating wibh a detector valve in an almost chronically overloaded con- , dition. In other words, the detector is being worked in such a way that the maximum undistorted output obtainable from it is insufficient to load the output valve. . Distortion introduced in this way is insidious, for ‘the reason that it is of a type to which the ear soon becomes atrophied. The trouble is one to which receivers. without an intermediate audio stage are particularly susceptible, and it is rather more likely to occur with a triode output ralve than with a pentode. The presence of detector overloading may be suspected when ‘the set. fails to respond readily to its sensitivity con-trol-reaction, r.f. valve bias, ete.after a certain point is' reached. Signals that are initially very weak become stronger, but others, just below the intensity required for full output. do not respond to the control in the proper manner. Apparent sharpness of tuning is also a good guide. If weak signals tune sharply, but strong ones, corresponding to approximately full volume, can be heard at the same strength over a mucn wider angular displacement of the tuning dial, it is reasonable to suspect that the detector is at fault. Failing emission in the valve may be responsible for this trouble; if it is not, an increase in detector plate voltage should be tried as a cure.