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    How to determine where hum is coming from

    PL 400 white oak cap kit, pl14 board, light upgrade, new output transistors, WA dc protection running quasi comp. Upon power up, there is a hum through the speakers that changes tone and then lowers. Where should I begin trying to eliminate this? Isolate the transformer from the chassis? I have...
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    Output transistor question

    (PL 400 quasi comp) I am replacing the old phase linear XPL909 transistors with new Onsemi MJ21196G transistors I bought from whiteoak. I have the installation list as to where to put what transistors. My question is half of my XPL909's are right side up with the printing on the transistors and...
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    Newly assemble pl14 rev G bias trimmers do not work correctly

    Hello, I recently added the DC protection, then new power caps from WO. I just assembled the pl14 rev G board. Started on a DBT no issues. went to adjust bias and my DMM readings are -.019 DC on both sides. Bias trimmers turned full CCW to start. Turning CW has no effect on the DMM. I am using...
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