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Bugera 333 Hum and radio station

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  • Bugera 333 Hum and radio station

    Hi, I just got a Bugera 333 (not millennium or XL). MF shipped it, opened it and played clean channel ... pristine, no hum, amazing. Tried channel 2 ... annoying hum and loud radio station coming thru, same with channel 3, but not as bad. One 12AX7 tube socket was very microphonic no matter what replacement I put in. Opened her up to see any cracked solder joints, poked around, nothing stood out, so I shipped it back.

    Ordered a replacement, got it and tried all channels and they sounded great. But my intention was to lessen the distortion, so I put a lower gain 12ay7 in V1 (which is labeled V8 on the board). It didn't change the distortion level, just made it quieter. So I went to put back original tube, but pulled chassis to get a better view of pin direction. Put tube in an all the same crap from 1st amp started, hum, radio, some slight microphonic when tapping around but not as bad. Hum gets louder when I turn up channel or master volume. I turned guitar volume to off, same hum, unplugged guitar chord from amp, hum/radio disappeared. One might think its the chord or guitar, but cant be because the clean channel is pristine quiet with no symptoms whatsoever, and I have about 5 or 6 other amps, and guitar/chord has no hum. When I touch the metal shield around the guitar chord with hand, it reduces the hum and radio to about 1/3 as bad. It sounds like a ground got loose when I pulled the chassis out. There is a metal foil all along bottom of chassis case, maybe that needs to make better contact, but not likely. I don't think its the tubes, because the 1st amp had same symptoms, and its not my house, because none of the other amps have the prob and 333 clean channel is perfect even at full blast.

    I'm stumped. I read other threads here about hum, but other thread had hum even with guitar chord unplugged. If I had this prob with 2 333's in a row, it must be more common, so I'm wondering if anyone had this problem and resolved it. Any help is appreciated, Thanks.

  • #2
    Update: Still no solution ... With amp on channel 2 (hum/radio channel) I turned all volumes/tones off except master, still hums and gets louder with volume. Pulled V1 only, no hum, pulled V2 only, no hum, pulled V3 only, no hum. Plugged guitar into effects return with amp on channel 2, NO hum, clean guitar sound perfect. One more interesting symptom ... While on pristine clean channel 1 (no hum/radio), I turn channel and master volume all the way up, no hum at all ... but ... when I turn channel 1 volume to zero there is a little static sound immediately before zero, guitar of course has no volume ... but at zero the hum/radio appears same as channel 2 problem. Apparently, channel one volume pot has an open circuit while at zero where the amp hot is not touching ground at bottom of pot resistance and this produces the hum/radio. So, this is what is happening to channel 2 always .. there must be an ungrounded element in preamp somewhere. I'll have to poke around. So strange that both amps had this problem.


    • #3
      Bugbear 333 Ground HUM

      Did you ever figure this out. I have a buddies 333 on my bench now with the same problem. No radio but the exact same issue you presented in your post. It's gotta be a ground issue.... Thanks