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Tube Radio HUMMING no stations or static...

Discussion in 'Home Brew' started by T23, Nov 9, 2010.

  1. T23

    T23 Active Member

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    I just got a tube radio in made by "Airline" it comes on but there are no stations and a loud hum, all tubes light.



    Instead of a variable cap. it has a coil with a rod that slides in and out....odd....

    Any ideas?

    T23
     

  2. office888

    office888 Active Member

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    Bad electrolytic caps is common.
     
  3. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Agreed. Sounds like the filter capacitors in the power supply section are bad.
     
  4. T23

    T23 Active Member

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    This is an in-line filament radio, it gets power directly from power mains...

    So basically I need to convert the older capacitor values to newer values and replace these paper-wax capacitors?


    T23
     
  5. office888

    office888 Active Member

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    :blink:

    Yes!

    I got a Heathkit DX40, and powered it up like a moron without checking anything. After ~1 minute of me tuning it into a dummy load, the 6146 final decided to go out.

    I went through it, and discovered quite a few of the caps were well out of tolerance. Two of the main power supply caps were bouncing in the range of 300v - 500v, even though they're supposed to be 400v caps.

    I replaced them with modern electrolytics, and now they're both solid at ~402v. She purrs beautifully on CW, although I still need to do some work on the MIC side of the circuit. :)

    It's safe to say, if there's a paper capacitor in there, it probably needs to be replaced. Wire-wound resistors MAY be finicky too, but that's far less likely. Also check for bad solder joints.

    You can go two ways

    1.) Damn authenticity, and just solder in a modern equivalent

    2.) De-core the paper capacitor, and put your modern caps inside it. Then reassemble the paper cap, and it looks original.

    Good luck with your project. :laugh:
     

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