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5g9 bias cap exploded!! Now what...?

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  • 5g9 bias cap exploded!! Now what...?

    I got my past tube issue solved and turned on the amp. So I turned it on and there was sound coming through but it sounded really choppy and almost like it was through a ring modulator or something. Then after about 45 seconds one of the 8uF bias caps exploded. I wired the 45 V tap to the negative side of a diode instead of a selenium rectifier, and then to the negative side of the bias cap. What do you think?

  • #2
    Diode backwards? The 45 V tap should go to the cathode (marked end) of the diode. When you power up, take a quick bias voltage measurement. Put your leads on, power up and you should see negative voltage to ground.

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    • #3
      Quote from previuos post:" I already had to sort out the discrepancy of the polarity of a selenium rectifier compared to a modern diode..."
      I read this & I am thinking "what did he say"
      Whether selenium or silicone, the "polarity" is the same.
      I do believe that your diode is installed backwards.
      The stripe goes to the transformer.
      Also the polarity of the electrolytic capacitor must be observed.
      The "plus" end goes to ground (negative voltage supply)
      Attached Files

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      • #4
        Originally posted by Jazz P Bass View Post
        Quote from previuos post:" I already had to sort out the discrepancy of the polarity of a selenium rectifier compared to a modern diode..."
        I read this & I am thinking "what did he say"
        Whether selenium or silicone, the "polarity" is the same.
        I do believe that your diode is installed backwards.
        The stripe goes to the transformer.
        Also the polarity of the electrolytic capacitor must be observed.
        The "plus" end goes to ground (negative voltage supply)
        Hi - Yes the polarity is the same, but the way selenium rectifiers were illustrated in these schematics was the opposite of how it actually was. I can't remember the reasoning, but it was to identify the polarity in a more logical way or something like that. Either way, the plus on the selenium rectifier in the schematic is the minus on a diode.

        That was the problem though. Thanks for the help.

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