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5e3 low freq. hum

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  • 5e3 low freq. hum

    Just built another 5e3 but I've got a humt that just won't leave me alone. Also the amp seems to do this plopping noise when full up. It's not a hum like a noisy grid wire but a low freq. hum. Other than that the amp would sound good. If i short out the .1 mfd caps at the plate resistor it stops. Could it be In the b+ or some weird parasitic? Some one help before I throw this thing though a wall !!!

  • #2
    Hello there - The " Plop Plop" you describe may be a cold solder joint or perhaps a bad tube. Try diffrent tubes first if that dosnet help you probably need to prob around in the amp with a wooden chopstick while the amp is on and see if you can get it to act up while you gentley moving connections around. I once located a defective pot this way.
    The Humm is another problem althogether and in order to help you isolate it more info is needed. . Did you use an artifical centertap for the heaters or does your power trans have a heater centertap? Is this a traditional layout in a standard chassis? Did you use sheilded wire from the inputs to V1? My first 5e3 hummed like crazy and it was just a matter of moving a ground wire to fix it, there is a lot of trial & error (and persistance) involved in tracking down & curing an amp that humms.

    Resistors not Transistors !