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Temperature Dependent Problem?

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  • richardscottw
    Hi all: I have been restoring an HW-101 to operating condition with the help of several people on this list. By replacing the final tubes and several leaky
    Message 1 of 3 , Mar 17, 2014
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      Hi all:
      I have been restoring an HW-101 to operating condition with the help of several people on this list.  By replacing the final tubes and several leaky caps and burnt resistors, I have it back to the point where I can go through the alignment steps successfully.  Yesterday I connected it to my antenna and had one QSO during which I got a good signal and audio report on 20 meter fone.  I left it idling for about an hour, then tried to check into a net and found that I had no power output on USB or LSB, though TUNE and CW were fine.  So the effect of leaving the radio on until it got hot led to this failure.  Today I reproduced the problem.  I can power it up and it works initially.  If I let it idle for an hour, then it fails in sideband.
      Reading through the troubleshooting section of the manual (Symptom 29, p. 151) leads me to suspect V1 and/or V16.  It seems to me that if it was a diode in the balanced modulator it would not be temperature-dependent.  Does this sound like a vacuum tube problem?  Has anyone else seen this particular issue?
      73
      -Scott N3SW-
    • Howie
      What you want to do is take voltage readings of those 2 tubes at startup,then take readings when it stops functioning. If no help,take power supply readings in
      Message 2 of 3 , Mar 17, 2014
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        What you want to do is take voltage readings of those 2 tubes at startup,then take readings when it stops functioning.
         
        If no help,take power supply readings in both conditions.
         
        That way ,you should find a big discrepancy some where.
         
        Let us kow what you find.
         
        ----- Original Message -----
        Sent: Monday, March 17, 2014 12:25 PM
        Subject: [Heathkit:Yahoo] Temperature Dependent Problem?

         

        Hi all:
        I have been restoring an HW-101 to operating condition with the help of several people on this list.  By replacing the final tubes and several leaky caps and burnt resistors, I have it back to the point where I can go through the alignment steps successfully.  Yesterday I connected it to my antenna and had one QSO during which I got a good signal and audio report on 20 meter fone.  I left it idling for about an hour, then tried to check into a net and found that I had no power output on USB or LSB, though TUNE and CW were fine.  So the effect of leaving the radio on until it got hot led to this failure.  Today I reproduced the problem.  I can power it up and it works initially.  If I let it idle for an hour, then it fails in sideband.
        Reading through the troubleshooting section of the manual (Symptom 29, p. 151) leads me to suspect V1 and/or V16.  It seems to me that if it was a diode in the balanced modulator it would not be temperature-dependent.  Does this sound like a vacuum tube problem?  Has anyone else seen this particular issue?
        73
        -Scott N3SW-

      • richardscottw
        It turned out to be V1, the 6EA8. I swapped it out with a borrowed tube and the radio performs normally. Now I just need to buy a good one for my radio. 73
        Message 3 of 3 , Mar 19, 2014
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          It turned out to be V1, the 6EA8.  I swapped it out with a borrowed tube and the radio performs normally.
          Now I just need to buy a good one for my radio.
          73
          -Scott N3SW-
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