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B15N...HUMMmmmm?

Discussion in 'Amps and Cabs [BG]' started by BLDavis, Aug 10, 2012.


  1. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    How much hum is acceptable? My '63 B15 is humming like crazy. I've had it re-capped and all new tubes, hum balance adjusted and it still has an annoyingly loud 60hz hum. Two different techs have worked on it and so far no luck finding the source. I've owned a couple of these in the past and I don't remember them humming like this. :bawl:
    Anyone have any ideas to share please help. (JimmyM ? ?) I want to use this amp in the studio this fall but it wont fly like this.
    Thanks, B.
     
  2. WingKL

    WingKL

    May 12, 2007
    A constant hum in a tube amp should not be too hard figure out by the process of elimination. Are you very certain it's 60hz and not 120 hz? Try pulling out preamp tubes starting from the input tubes on all the way to the phase inverter and see if the hum goes away or reduces. If it does, then the source of the hum comes from the preamp tubes. If the amp filament supply shares the same transformer as the high voltage supply, there is a good chance that the rectification noise is being coupled to the filament supply as harmonics of a 120hz hum. You can test that by putting a switch on the filament supply and quickly tuning it off while the amp is humming to see if that affects the hum. If it is a true 60 hz hum, try rotating your power transformer to see if changes things. I'm betting your techs aren't really experienced with tube amps if they can't figure it out.
     
  3. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If operating properly, your amp should be dead quiet.

    There are a few things to look at first:

    A bad tube. If you have spares, swap them out one at a time from the first pre-amp tube down the line.

    When the power supply caps were replaced, was an isolation washer used on the cap can? There is only supposed to be a single ground at the input jacks. If the cap can is in contact with the chassis, it will hum.

    A bad solder joint on a power supply cap will cause a hum.

    60Hz tells me to look at the heater circuit. If the hum adjust pot is bad (open somewhere in the rheostat) the amp will hum.

    If there is a center tap on the power transformer heater winding, make sure that it isn't grounded. Either you ground the 6.3V heater CT, or you use a hum pot, or you create an artificial center tap with two resistors. You can only use one of the three.

    There is supposed to be an isolation washer on the 8 ohm ext. speaker 1/4" jack. Not having the washer present will cause a ground loop and hum.
     
  4. BogeyBass

    BogeyBass

    Sep 14, 2010
    Lead Dress or missed cold solder, input jack connections/chassis ground
    or high line voltage. check preamp tube bad 6SL7 can hum like crazy. and the ground connection with speaker cable for the safety shutoff
     
  5. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    Ok,
    I tried pulling the pre tubes one at a time as suggested by WingKL. The hum stopped when I pulled the one next to the power tubes. I dont have any extra tubes to substitute with right now so I'm stuck.
    Thanks for the replys and advice.
    B.
     
  6. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    At least it was an easy solution. New and NOS 6SL7's are pretty reasonable.

    BTW, I know this will probably be a dumb question, but you do have the other channel's volume turned all the way down, don't you?
     
  7. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    Yep....:p......But it hums anyway.......and now I'm off to FlipTops.com............
    B.
     
  8. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    fliptops.net . .com sends you to some no-name spyware-attracting search engine.
     
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    You can do another test. Take the tube from the third socket (V3) and swap it with the tube from the first socket (V1). Don't get the tubes mixed up.

    It should hum. Now remove the first tube and see if the hum is gone. If yes, then probably the pulled tube is bad. At the same time, with V1 removed, you should be able to plug in to channel 2 and the amp should work and there shouldn't be any hum.
     
  10. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    I thought of trying that late last nitght. Still no luck. If there's a tube plugged in the V-3 socket it humms. At least that narrows it down some more. I'm pretty sure all my tubes are ok, and that the problem lies in the V-3 socket region. Now to find a "competent" tech to fix it. Which aint easy since I live out in the sticks.....:meh:
    Anyone familiar with "The Amp Shop" in Asheville NC? They're an hour away from me.
    Thanks, B.
     
  11. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    Thanks for the heads-up.

    I went here, http://www.fliptops.net/ ,with no problems.
    B.
     
  12. My tech is in Spartanburg SC, an hour south of Asheville. I highly recommond him and he's all about some Ampeg.
     
  13. BLDavis

    BLDavis Old enough to know better.....too young to care! Supporting Member

    May 21, 2009
    Ellenboro, NC
    I'm only 45mins from SparkleBurg. Can you give me his contact info?
    Thanks, B.
     
  14. PM sent.
     

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