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Antique Radio Technical Forum
The Hum From The Speaker

Posted by Ed M on 04/13/2009 13:28

:Whenever this kind of thing occurs, it is always best to start at the output of the radio and move back through the radio. This would include a tune-up. First check the audio stages to make sure that you can send a signal (hum from finger) through all the way from the volume control. Then check the IF stages with your signal generator. Then check all of the front end circuits for proper alignment and for oscillator operation (which you say is working). This procedure will reveal just about everything you need to know.
:There isn't much to a radio except capacitors, resistors, and coils (and tubes). If you get to a dead point, check coils for continuity, capacitors for shorts (and opens), and resistors for opens (and drifting). If all checks out well, check to see that you can tune coils to frequency. If you can't, there may be a partial short within the coil. If this is the case, it would help to have a chart of DC resistances for the coils.
:...And finally check ALL wiring, and check individual tube element continuity (can be done with most tube testers).

Good advice. When the oscillator is working, and the set has audio output and gain, and someone tells about the radio being taken to a shop and found to be non-repairable, the most common problem I have found is one of the IF transformers. Either an open winding (wire was stripped with acid before soldering, and not cleaned well - over time the remaining acid eats the wire in two), or leaching of silver in one of the internal capacitors. Other folks may have had other experience.

The Hum From The Speaker 
Johnny 04/11/2009 14:58 
Thomas Dermody 04/12/2009 00:16 
Ed M 04/13/2009 13:28 
Johnny 04/13/2009 19:10 
Thomas Dermody 04/13/2009 21:05 
Lewis L 04/13/2009 21:18 
Edd 04/13/2009 22:43 
Johnny 04/14/2009 07:01 
Edd 04/14/2009 11:27 
Doug H 04/15/2009 11:38 
Johnny 04/15/2009 12:01 
Doug H 04/15/2009 12:40 
Johnny 04/15/2009 17:51 
Johnny 04/15/2009 11:54 
Johnny 04/15/2009 19:58 
Johnny 04/16/2009 02:15 
The Rework Is Done 04/15/2009 23:21 

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