One of two channels works on Ampeg Gemini I amp

Discussion in 'Pro Audio' started by questionz_99, Mar 2, 2006.

  1. questionz_99

    questionz_99 Guest

    I have an Ampeg Gemini I amp that includes two sets of inputs (Channel
    1 and Channel 2), each labeled "Guitar" and "Accordion".

    This is an old tube amp, with four tubes.

    Only Channel 1 works. Channel 2 is silent. What should I check first on
    this amp to try to get Channel 2 working?

    Thanks.
     
    questionz_99, Mar 2, 2006
    #1
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  2. questionz_99

    Paul Stamler Guest

    Swap the input tubes on the two channels. If Channel 2 now works and Channel
    1 doesn't, you've identified the bum tube. Replace it.

    Peace,
    Paul
     
    Paul Stamler, Mar 2, 2006
    #2
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  3. Shoot the accordion player in the face --immediately.

    Have the Guitar Player buy a Hughes & Kettner Triamp MKII asap.
    He probably needs to learn to link his 7 Modes as well as his
    5 Blues scales, learn how and where both overlap -then get
    it all under his fingers with practice. Next, he'll need
    to intuitively relate to the chords on top of both and funk up
    on that rhythm. Jam!

    My work here is done :). mvm
     
    The Iconoclast, Mar 2, 2006
    #3
  4. questionz_99

    leutholl Guest

    Am Thu, 02 Mar 2006 00:25:23 -0800 schrieb The Iconoclast:
    ;-)
     
    leutholl, Mar 2, 2006
    #4
  5. Seconded. If that doesn't work, or you don't know which tube is
    which, write back.

    -Scott McKnight
     
    Scott McKnight, Mar 2, 2006
    #5
  6. questionz_99

    ron Guest

    I have one of these. Send me an e-mail offline and maybe we can sort
    it out. later, ron
     
    ron, Mar 2, 2006
    #6
  7. questionz_99

    Slim Guest

    First you check your preamp tube(s). (The little ones)
    There is also a sleepy little yahoo group just for Ampeg amps that you
    might get some tips from.
    http://launch.groups.yahoo.com/group/ampeg_guitar_amps/
    Best thing to do is to make friends with some kind of local tech who
    doesn't mind helping you once in a while with old tube stuff. The
    folks in here are probably not too interested in boring old tube guitar
    amps - they have nano-nuke-servo powered PA systems to worry about.
     
    Slim, Mar 2, 2006
    #7
  8. questionz_99

    Slim Guest

    OOPS! I stand corrected - the nano-nuke-servo powered PA techs just
    got outgunned by caring warm and fuzzy Ampeg fans!
     
    Slim, Mar 2, 2006
    #8
  9. I know others here mentioned to check the input tube on the problem channel
    (which isn't a bad idea, and make sure it's simply seated in there properly
    in other words take it out make sure the pins are not bent and then
    carefully put it back in correctly) but it could be a bad wiring connection
    somewhere around those channel two input jacks or that tube as well.
     
    news.west.cox.net, Mar 3, 2006
    #9
  10. questionz_99

    questionz_99 Guest

    Thanks to all. You're a great group. I'd like to proceed carefully with
    this project. So, here's where I stand now:

    I understand that the two smaller tubes (on the Channel 1 side) are
    pre-amp tubes. There are two bigger tubes on the Channel 2 side, which
    I suppose are the amplifier (or input?) tubes.

    To reiterate, Channel 1 works and Channel 2 does not work.

    What is my next step? Should I swap the pre-amp tubes and see what
    happens, then swap the larger tubes? Can I do that safely?

    (I'll check the wiring, too).
     
    questionz_99, Mar 3, 2006
    #10
  11. You should try swapping the preamp tubes the small ones should be 12ax7's I
    would think.

    You don't sound like you know what you are doing so I would advise you not
    to open the amp up and mess with wiring or anything inside the chassis as
    there can be high voltages in a tube amp even after it is unplugged.

    You should be perfectly safe pulling/swapping tubes. I would strongly
    suggest you unplug the amp first and handle the glass part of the tube, in
    other words no sticking metal objects under the tube and touching the pins
    while they are still in the socket.

    If swapping the tubes switches your problem to the other channel you can
    guess you have a dead tube but I would say that's fairly unlikely as old
    preamp tubes usually go on forever at basic function anyway.

    If that doesn't work for you really need an amp tech, poking around inside a
    tube amp if you don't know what you are doing isn't the most healthy of
    practices.
     
    news.west.cox.net, Mar 3, 2006
    #11
  12. questionz_99

    questionz_99 Guest

    Turns out the problem was the ECC83/12ax7 preamp tube for Channel 2.
    Both those tubes were contained in metal heat shields.

    Would it be of any advantage to purchase a "matched pair" of 12ax7s? Or
    should I just replace the one tube?

    Matched pair available here:
    store.triodestore.com/12ax7ehmp.html

    A couple of notes:

    The "bad" tube in Channel 2 doesn't produce sound, but it does glow
    when I turn on the power.

    When I swap preamp tubes, I get plenty of sound in Channel 2. But I
    also get a wave of radio-like static that builds to a peak, stops
    suddenly, rests and begins again. Can anyone explain why this static
    occurs?

    Thanks.
     
    questionz_99, Mar 10, 2006
    #12
  13. questionz_99

    Scott Dorsey Guest

    There is no reason to use a matched pair. Pick up whatever 12AX7 type
    you like (I have liked the JJs, but I'm not a guitar guy). Put it in.

    Listen. Swap the tubes around and listen again. Pick whichever combination
    sounds better to you.
    If this is Triode Electronics in Chicago, they are honest guys and fair
    dealers and I cannot recommend them highly enough. Ned is a good guy. If
    they are someplace else, I dunno.
    Because something is oscillating, possibly due to a bad cap.
    --scott
     
    Scott Dorsey, Mar 10, 2006
    #13
  14. questionz_99

    Paul Stamler Guest

    You don't need a matched pair, but I think I'd go ahead and replace both
    12AX7s. Replacing both *might* solve your wave-of-static problem too. Or it
    might not, in which case it's time to replace coupling capacitors.

    Peace,
    Paul
     
    Paul Stamler, Mar 10, 2006
    #14
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