XPost: sci.electronics.repair   
   From: legg@nospam.magma.ca   
      
   On Tue, 31 Jul 2012 16:48:00 -0700, "William Sommerwerck"   
    wrote:   
      
   >> The "rumble filter" circuit in this tuner is sort of interesting.   
   >> Rather than inserting a low pass filter in the audio section,   
   >> it changes the time constant of the AFC network. When the   
   >> time constant is lowered more of the "rumble" frequencies   
   >> are feedback cutting the low frequency audio response. This   
   >> means that the "rumble filter" won't work when the AFC is off.   
   >>  Also the labeling for the "ON" and "OFF" positions of the   
   >> "rumble filter" switch appear to be reversed.   
   >   
   >This falls into the "It's not a defect, it's a feature" category.   
   >   
   >If the AFC time constant isn't long enough, the AFC will try to null out the   
   >audio's bass.   
   >   
   >I've never heard of a "rumble" filter for FM tuners, but it might have made   
   >sense in the days when phonograph records were the principal program source,   
   >and perhaps even during live concerts (when traffic and subway noise might   
   >have intruded).   
   >   
      
   All done. Bad contact in the socket of the local oscillator. Had   
   cleaned the tube pins, but sockets presented a more serious challenge.   
      
   Output coupling cap had shorted as well. Don't expect some amps would   
   like that. Only noticed on the scope.   
      
   RL   
      
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