GK mb800 problems

Discussion in 'Amps and Cabs [BG]' started by JGbassman, Oct 4, 2016.


  1. hey all, I've got a gk mb 800 I've owned and gigged pretty heavily over the last 5 years. About a year ago it started giving me problems, with the sound almost cutting out, where it was Bearly audible with what sounded like all of the lows cut out, to farting out really bad. This isn't consistent, where it might act up for a while, then work fine for a couple of weeks or so before going back to usually the low volume sound. It sounds distorted at times too.

    I've gone through my entire rig, troubleshooting gear until I finally have it pinpointed in the mb800 as the culprit. It's not buzzing or making any high pitched sounds as I read have been some issues in the past.

    It have been a good amp and I'd like to get it fixed, I'm just wondering if anyone has any ideas where this might be coming from. At one point the power switch wouldn't shut off so I took it apart and fixed the little spring mechanism. The power button has been working fine ever since so I don't suspect the issue is there.

    Is this something I would have to go through gk for?
     
  2. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Have you tried the EFX loop loop-through test?
     
    jnewmark and wave rider like this.
  3. I have bypassed the preamp plugging into the power amp directly with the same results.
     
  4. Jim Carr

    Jim Carr Dr. Jim

    Jan 21, 2006
    Denton, TX or Kailua, HI
    fEARful Kool-Aid dispensing liberal academic card-carrying union member Musicians Local 72-147
    shoot-r, Jim C, petrus61 and 2 others like this.
  5. Thanks Jim, I'll give them a call sometime this week
     
  6. wave rider

    wave rider

    Jan 5, 2005
    Try the full jumper, the little switch that gets corroded is on the loop in.

    Oops, may have read your post wrong...

    =wr=
     
  7. shoot-r

    shoot-r

    May 26, 2007
    Illinois

    BIG +1!

    O.P., give G.K. customer service a call.

    When my G.K. MB2-500 started giving me a problem awhile back, G.K. customer service was absolutely GREAT.

    G.K. repaired the head in the amount of time they said they would and at the price they said they would, (something I can't say for another manufacturers amp I also had at that time and was having problems with.....A*peg.)

    Bob G. even e-mailed me to make sure I was happy with the MB once it was repaired and returned to me.....
     
  8. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    JBbassman...I also recently aquired a used MB800 via Reverb. Needless to say, the amp was packed like a bologna sandwich when it was shipped, so that kind of set off some alarm bells early on. I wasnt overly concerned since Ive done business thru Reverb quite a number of times in the past, and all previous deals left me more than satisfied. Anyway, the amp sat for awhile (approx 2mnths) til I found a speaker cab to pair it with. Outside of powering the unit ON after it arrived and checking output with a meter, there wasnt much I could do short of using headphones to hear it until I had a compatible cab. Subsequently, I eventually came across a worthy deal on a GK-NEO [email protected] (also via Reverb) and I made it happen. After playin thru the cab for less than an hour at a modest level, I wanted to "drive" the AX7s a bit and experiment with sound. Almost immediately after increasing the volume, I had what seems like the very same issue you reported previously with ur GK. Loss of signal. From a scratchy, barely audible wet fart type quality, to intermittent total loss of signal. I was really hopin to find it was all just a bunk cable or a dead 9volt in the bass pre-amp....no such luck. I realize internal damage could have happened during shipping, but I suspect the seller was aware there was an issue, despite neglecting to ever mention a problem when he sold it. Ahhh yes indeed, only the very best that mankind has to offer for me thank u very much. Someone needs to inform GK, its always best to default to "worst case scenario" before anyone assumes it to be common sense for people to actually realize 1960s era amps will have a much different during a modern re-design of a product that didnt exsist as a lightweight, convenient, and powerful package. Just based on available materials of the past, an amp of comparable power probably weighed btween 50-100 lbs and was 6-8 times the size of an MB800 currently. It was fairly common to just manhandle an old school amp back in the day...there wasnt really reason to worry about functionality either. The very nature of an amp of similar capabilities of that day and age, considering the commonly used materials, it was expected to BE cumbersome, heavy, and basically indestructable.
     
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Does the MB-800 have "12AX's"?

    Have you considered that perhaps the seller didn't have a problem and that this is new and possibly related to the shipping? Perhaps it's simply bad luck?

    I would suggest seeking out a GK authorized service center to troubleshoot and fix your amp properly. Easy solution.
     
    jthisdell likes this.
  10. mmbongo

    mmbongo Regular Human Bartender Supporting Member

    Aug 5, 2009
    Carolinas
    There are no tubes in an MB800. 12AX’s or otherwise.
     
    agedhorse likes this.
  11. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    Idk. When he boxed it up, he never took the time to protect it whatsoever really. It amounted to putting a crumbled up sheet of newspaper in the very bottom of the box and setting the amp on top. The top was entirely unprotected. And the GK Fusion MB800 definately has 3 AX7s in the pre-amp. I probably left out "Fusion" in my prior post. As I mentioned, its now day two without furthur issue since re-seating the one tube and connector that definately looked pretty loose
     
  12. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    I got another few hours of playing in today without incident. Im happy that seemed to do the trick and it didnt involve sending it out for a repairs. I work in the A/V field, so I have access to plenty of rack units, road cases, and shelving. I found an old 3 space Rhino case laying around in our shop. Rather than just leaving it collect dust in the corner, I mounted the amp securely to the proper style shelf and put a power conditioner in the upper rack space. I had the extra space, so what the hell, right? Hopefully that will protect the head and help alleviate some vibration sittin on the cab. I feel better havin somthin around it at least and the best part....it didnt cost me a thing.
     
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    The Fusion part is kind of critical information...
     
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  14. mmbongo

    mmbongo Regular Human Bartender Supporting Member

    Aug 5, 2009
    Carolinas
    You have an MB Fusion 800, not a Fusion MB800. MB800 is a different, tubeless, amp.
     
    LouBass likes this.
  15. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    Youre absolutely right. MB Fusion 800 is the correct. This is the first GK gear Ive come to own in my 30yrs of playing, so I apologize for my bein unfamiliar. Ive always had interest in GK gear and respected what Ive heard over the yrs. Ive always been open to using GK if the opportunity happened to arise, it just never did. There isnt much as far music stores in my area and most of the previous gear Ive owned pretty much came about by "fallin into my lap", im sure u guys can relate. My area sucks for aquiring most things, except for maybe alcohol. Overall im really happy with the sound im getting with GK. Its definately versitile. Ive tried Orange, Ashdown, Hartke was my "go to" rig for awhile until I picked up an Ampeg SVT head on a whim cuz I needed somthin fast. I paired it the SVT with an Eden cab. I like the Ampeg and the GK equally Id say. I wouldnt claim either sounds any "better", u can dial in a great sound with either, theyre both just unique in their own way. Im curious to hear ur thots and what uve learned thru prior experience with different gear. Ive always utilized a Tech 21 Sans Amp on all my rigs since they started popping up yrs ago. I tried somthin slightly different this time and picked up the Dug Pinnicks twist on the Sans Amp, I dont "dislike" it, but its noisy as all hell for starters. Im thinkin the V2 version Sans Amp will be a better, more versitile and rounded fit. What sorts of goodies do u gents have goin on?
     
  16. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    Anyone have prior knowledge or experience with EBS/Reidmar at all? Somthin about what Ive heard left an impression...im definately curious.
     
  17. jthisdell

    jthisdell

    Jun 12, 2014
    Roanoke, VA
    So have you checked the tubes or re-seated them? May not be the problem but definitely start there.
     
  18. Brian P

    Brian P

    Feb 21, 2020
    NEPA
    Yes. I carefully removed the cover last night bcuz a bad tube or a tube not seated was initially what I suspected. I noticed when it had acted up prior, if I tapped sharply on the top of the head, just above where the tubes are located, the noise would immediately clear up. Based on that, I figured Id open it up and find somthin fairly obvious, and I did. I found one of the Molex connectors, right in that same area near the tubes, looked like it had been pushed on with one of the pins not aligned. U could clearly see the outer (female) portion of the connector was actually distorted cuz it wasnt locked in completely or correctly. I was very careful to remove it from the socket, re-aligned the pins, and reconnected it firmly. Everythin has seemed spot-on since doin so. No more noise or crackling wet farts. Thanks to everyone in the thread for bein super cool and offering thots and ideas. Much appreciated.
     
    agedhorse likes this.
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    Primary TB Assistant

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