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Old Grundig Valve Radio Sound Problem

Discussion in 'Troubleshooting and Repair' started by octavez, Apr 20, 2012.

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  1. octavez

    octavez

    2
    0
    Apr 20, 2012
    Hi,

    I got an old Grundig Valve Radio, KS560: http://www.radiomuseum.org/r/grundig_ks560_1.html

    It is working well but since few days the sounds start pumping like a heart and it sounds really bad. I'm guessing that it's a valve which is probably dead but since there are 8 tubes in it I'd like to know if there is a way to isolate it. I have almost no knowledge in this domain!

    Thank you!
     
  2. shrtrnd

    shrtrnd

    3,821
    519
    Jan 15, 2010
    Do you know anybody with a tube tester?
     
  3. KJ6EAD

    KJ6EAD

    1,114
    159
    Aug 13, 2011
    You could be experiencing a condition known as "motorboating". Look it up on Google or in the Radio Museum. It can be caused by something as simple as a leaky bypass capacitor allowing RF into an audio amplifier stage.
     
  4. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    Motor boating is almost certainly due to bad capacitors. I would go for the HT bypass smoother capacitors. You could get a 10uF or so capacitor and temporarily connect this across the bypass capacitors to find the faulty one(s).

    Don't kill yourself!
     
  5. octavez

    octavez

    2
    0
    Apr 20, 2012
    Thank you really much! I'll investigate it!
     
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