GK 200MB Repair Help!

Discussion in 'Amps, Mics & Pickups [DB]' started by goodgig, Jul 19, 2013.

  1. I have one of the old GK 200MB combo amps. The hex nut on the input jack was loose. So I got out a wrench, over tightened it and the threaded receiver broke off. Turns out to be plastic. I took the top plate off the amp and saw that the jack is soldered directly to the circuit board. Not sure if that part is available. I still have the broken off pieces. Do you have "input" how to repair this? Love the amp but it makes an ugly doorstop. Thanks.
  2. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    A replacement part should be readily available. The right way to do the job is to de-solder the jack from the board and solder in a new one. It's usually a relatively simple exercise for someone with soldering skills. The ugly solution, that I don't recommend, is to put some glue around the barrel and collar of the jack and adhere it to the front panel. The downside is that you'll make the job tougher for someone who would later want to do the job the right way. There's also the risk that you'll be on a gig, plug in your instrument, and have the glue-joint break.
  3. Drub - Thanks for the response. I was going to try the ugly solution but too risky if it falls apart in the middle of a performance. I just called a local amp repair shop and they have the part in stock. I guess it's a reasonable repair to make after 25 years!
    krejza likes this.
  4. MR PC

    MR PC Inactive

    Dec 1, 2007
    Probably a good time anyway to go over the amp innards and tighten/resolder things up after 25 years of use..That amp is a fave of mine, hard to find these days.:)
  5. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Tighten things up, clean controls-- yes. Resolder? Not a good idea, unless there's evidence of failing or cracked joints. The amp is going to a repair shop. If the OP wants it "tuned up," they'll know what to do. With older amps, one can often cause more problems by looking for things to fix that ain't broke. :)
  6. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    Mr. PC,
    Very true, the 200MB's sounded different than their newer counterparts. The EQ voicing and warmth is just ideal for Double Bass. Since they had a metal case, you would think there would be more of them around, but that's not evident on Talkbass, Craigslist, or Ebay. The MBS and MB200 head are pretty close to the 200's, but there are subtile differences in it's timbre.

    krejza likes this.
  7. Thanks again guys. If it appears that I'm dangerous with a wrench, you ought to see me with a soldering iron! Going into the shop this week. You're right Ric. This is one of the best amps for upright. I have no interest in using anything else!
  8. CTForde


    Oct 9, 2012
    I have a ground-hum in mine EVEN WHEN IT'S JUST PLUGGED IN - even with the oowe switched off.
    any ideas?
  9. Another solution would have been to use an ordinary panel jack and solder short wires from it to the board. Old-school yo.
  10. This is a common problem with the GK 200MB. The power switch on this amp does not shut off power to transformer, which is mounted in the speaker compartment. The current flowing through the transformer is heard through the aluminum panels the amp case is made of, which are working like a soundboard. You can try tightening the four large, panhead screws that hold the transformer in place, which are located on the back of the amp near the bottom. These screws can get loose after awhile, which tends to increase the amount of hum being heard through the case.
    Last edited: Apr 18, 2015
    mormoyboy likes this.
  11. CTForde


    Oct 9, 2012
    thanks - that makes sense!
  12. DBW


    Apr 17, 2015
    Sometimes this can be a power source issue as well. Many other appliances and such (lights etc), plugged into the same circuit can cause grounding feedback loops, you can also (just to see if it is the issue) try ground lift plugs (I recommend properly grounding the ground tab with a wire separately), reversing polarity, and different circuits as well. When it definitely is not an issue from power source then it would have to be something inside your amp, as said above, transformer ground, solders, a multitude of other things.