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GK 400RB-II Circuit

Discussion in 'Amps and Cabs [BG]' started by rawlsjk, Nov 29, 2003.

  1. Hey everyone, this past week, the circuit in my GK 400RB-II burned up on me. Actually, I believe it was only one particular capacitor. But I don't know the extent of any other damages to the circuit. I was wondering if anyone knew of a way that I could just replace/purchase the circuit board for the GK 400RB-II (not the front panel board, but the board with the heat sink, fan, etc.) without having to purchase another GK amp? Thank you for your time and help. God bless you all!

  2. What Cab/bass/setup were you using? How hard were you pushing it?

    I had a GK800 that blew up, and had it fixed by a buddy of mine. I got the power transistors free, but still managed to spend $125 on other parts and his time. If I would have bought the power transistors, it would have added about $50 more. the whole board new would probably be as much as buying a used 400RB II - they go on ebay for less than $300, and I've seen used ones for less than that.

    Check it out though, I might be wrong.


    p.s. If you decide to junk it lete me know, I do fix them up myself. It might be worth a little to me. Or if you're clever, you could use if for a preamp!
  3. I really appreciate you taking out your time to help me out here. Let me explain what happened and that might clear some things up. LOL. I was playing my bass while in church and (not thinking), I had something covering where the heat is released. I'm guessing the circuit overheated and I noticed that the protect light came on and my sound went. So I waited a couple of days and then tried to turn it back on thinking that maybe the amp had shut itself down before doing any massive damage. But I cut the amp on and then the fuse blew, I replaced the fuse and then some of the actual circuitry burned up (looked like one capacitor). I am going to start looking on EBAY to see if I can find a GK400, because I've gotten accustomed to its sound and was just learning how to really fine tune the sound that I am trying to create. Thanks a lot. Take care!!

  4. Jason,

    I just saw a GK400RB advertised on bassgear.com a few days ago.

    You might want to check out Harmony Central too.

    Harmony Central Bass resources


    oh, and don't forget that if you want to talk to me abou the dead GK, I'd possibly be interested.

  5. rumblinbass


    Aug 22, 2003
    Wimberley, TX

    I would also be interested in the "dead head" as well.

    Sounds to me like you did a number on that amplifier. Typically, from my experience, when an amp overheats it's the output transistors that fail. When they fail they can create a short between power and ground. So when you turn it on, you will burn up capacitors and fuses and all sorts of things (possibly).

    Let me know if you are interested in getting rid of it and if it doesn't work out with basstrader.
  6. I'm going to see what I can do with the circuit (if I can get it fixed or not). Just out of curiousity, how could I turn it into a preamp? I don't think I'm going to junk it though. I'll start looking around for another GK Amp. Take it easy.

  7. rumblinbass


    Aug 22, 2003
    Wimberley, TX
    If I remember right, on my GK 700RB the pre and power stages were on seperate circuit boards entirely. You'll have to double check...hope you have experience with electronics.
  8. To make it a preamp, you would need to take the power amp section out. Not to hard if the pre and power are on seperate boards, like Rumbler said. Also the power supply needs to be working, and from your description, it sounds like it's fried.

    Other GK amps:
    800RB - some of the preamp is on a separate board, some not.
    200RCB - older version of MB150, all on one board.

    Don't know much about other GK's as I've never been inside one. The newer ones might be different too.


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