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GK MB500 (MB2-500) Supply Voltage Change

Discussion in 'Amps and Cabs [BG]' started by Dizzy_G, Dec 8, 2010.

  1. Dizzy_G


    Oct 15, 2008

    Opening your head and performing this mod will void your GK warranty.
    I don not undertake any responsibility for any one performing this modification.
    If you are not comfortable working with high voltage equipment or do not know what you are doing please take your head to a qualified GK service engineer, if you have a service engineer in your area go to them anyhow.
    I take no responsibility if you blow your head/fingers/brains etc.
    This guide is posted for competent people who need to change the voltage of their head for what ever reason and simply understand what they are doing.

    On with the show, picture of the jumper to change in order to switch an MB500 from 110v to 220v operation. Move the blue wire jumper to the voltage position required.
    I had a look for a photo/guide previously and couldn't find anything much other than verbiage so I decided to post if anyone needs help.

    To clarify further on the fuse, the PCB is marked "T5A 250V", I think this might be a one trick pony for both 110v & 220v.
    However if you wish to change the fuse I suggest the following.
    Half the fuse value to 2.5A, ensure it is a T "Time Delay" to allow for more current draw on start up. From Ohms Law, W=V*I, so for 110v we get 110v*5A=550W, inversely for 220v we get, 220v*2.5A=550W.

    This fuse spec is the perfect replacement @220v operation, Maplin have the same fuse in a bag of 10 for around €3.
    A 2.5A rated fuse will offer more protection when running at 220v, than a 5A. For a 30c piece I will be making this swap myself now that I put a bit of effort into writing this.


  2. Would this work on the MB200 as well?
  3. Awesome, thanks so much for posting this. Been meaning to ask this for a while but didn't get round to it since I'm not playing in any 110V countries anytime soon.

    Downside, probably could have got one from the USA for way cheaper and just changed the jumpers....
  4. rag


    Mar 24, 2003
    Robert A. Gallien, President Gallien-Krueger
    If you did that you would not have a warranty, except in the USA.
  5. Yep aware of that, would have to weigh that up with the saving.

    Either way, very happy with my amp Bob! Only thing I would change is the blue LED :bag:
  6. Dizzy_G


    Oct 15, 2008
    Bob, firstly well done to all at GK, this is a fantastic head and is very well engineered. I do not mean to cause any offence to GK in anyway by posting this. It is meant as a guide to those who really need it.

    By posting this I'm not trying to undo any of GK's hard work or service agreements etc., it is purely for people like myself who are not worried about warranty issues and happy to take on responsibilities of their own.
    I love this head and hopefully won't be changing for quiet some time.
    By the way I love the blue led, they are not as bright as some other heads.

    To clarify further, I bought mine second hand in the US and with no warranty card (which would not be valid at home anyhow) and I was not too worried about it tbh, I got a great deal on a head I really wanted. For me changing the jumper was a 2min job.
    I do not know of any service engineers in my country. anyone not happy to work with electronics or does not understand what they are doing should not attempt this. I am very comfortable doing this type of work therefore it was not a problem for me.

    _DOM_P_, I'm not sure as i don't own an MB200 so I can't answer this with any certainty what so ever, my apologises.

    On the fuse if people were paranoid you could halve the value to 2.5A, ensure it is a T "Time Delay" to allow for more current draw on start up. From Ohms Law, W=V*I, so for 110v we get 110v*5A=550W, inversely for 220v we get, 220v*2.5A=550W.

    This fuse spec is the perfect replacement @220v operation, Maplin have a bag of 10 for around €3 so they should see thru a few decades of playing.
  7. davidprice


    Jan 1, 2005
    Any idea what the fuse value would be for the MB200 (200 watts into 4 Ohms - though I've also read 240 watts) - rather than the 500 - if running in Europe? I expect it is simply halfing the value (?)
  8. Dizzy_G


    Oct 15, 2008
    Following Ohms Law you can halve the value for 220v operation over 110v. If you open one can you take note to see if it uses the ICEpower50ASX2 amp?

    Ensure the replacement fuse is rated the same as the one being replaced, if there is a T for time delay ensure it is replaced with a Time delay fuse.
  9. davidprice


    Jan 1, 2005
    Thanks, Dizzy. That's clear.

    I would be having one brought from the US so I don't have it to open yet.
  10. ialma

    ialma Supporting Member

    Jul 1, 2006
    South Italy
    Thank you Dizzy.
    I performed this operation myself this morning on my MD500 without the slightest problem.
    The head seems to work perfectly, I'll keep you tuned.
    A big thanks to you and no thanks to GK's customer service which did not answer my mail.
  11. Just so I have it straight, it is just a question of switching the jumper and changing the fuse? I am NOT going to try this myself, but having an understanding of what is needed will help me understand the size of the task so I don't get abused by the service tech I'm going to take it to.
  12. Doctor Roberts

    Doctor Roberts

    Oct 22, 2007
    Has anyone tried keeping the same fuse and just switching the jumper, for 220v purposes?

    Thank you.
  13. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    You must ALWAYS change the fuse to one half its value if you change from 120 to 240V. It's imperative for the safety of your amplifier.
  14. DavePlaysBass


    Mar 31, 2004
    That's a conservative way of looking at it and may be correct. However, if the fuse in the 120V version has the approriate voltage rating for 220V, it may provide the necessary safety function just fine at the same current rating. Over the useful range of operation, a fuse is merely a current controlled switch (as i suspect you probably know). Under fault conditions you need enough current to open the fuse so that things don't catch on fire or create a shock hazard.

    If I was selecting a fuse for such a dual voltage application, I would try to use the same fuse for both. But sometimes thats not possible.

    If you are going from 220V to 120V, you would find out pretty quick if they required different fuses as the 120V pulls twice the current and could open a fuse optimized only for 220V operation. But going 120V to 220V (again assuming the fuse is 220V rate), it is hard to tell.
  15. davidprice


    Jan 1, 2005
    Just an FYI if anyone does this on an MB Fusion (I did on both the Fusion and MB200) that the Fusion has TWO jumpers that need to be changed. I believe one for the preamp and one for the power section. They are labeled (smallish) on the circuit board). Easy job.
  16. Doctor Roberts

    Doctor Roberts

    Oct 22, 2007
    Thanks Paul.

    I received my MB200 straight from Amazon today (whom I suppose ships 110v by default), and the circuit looks exactly like the reference image below:

    ImageShack® - Online Photo and Video Hosting

    If you look, there's a "T2.5A 250V" near the jumper (which is also on my amp).
    Do I still need to replace the fuse?

    And another question:

    In what final position should the jumper stay,considering the picture, for 220v purposes?

    I looked around, but I won't do it myself. Still, I'd like to know this to double check, since it'll be pretty much like going to the mechanic (inverse relationship between the amount of knowledge you've got, and the amount you end up paying).

    Thanks for your help.
  17. davidprice


    Jan 1, 2005

    That jumper covers 2 of the 3 tines so it just moves over 1 (the center tine is used for both/either 115/230).

    I was told the existing fuse value was okay - but I don't know if that was absolutely authoritative. I've gigged the amp quite a bit with no problem.
  18. Doctor Roberts

    Doctor Roberts

    Oct 22, 2007
    Thank you. I'll let you know how it turns out ;)
  19. Doctor Roberts

    Doctor Roberts

    Oct 22, 2007
    David and all, just to make sure (I'm not planning on doing it myself, so chill out. It's for learning and avoiding rip-off purposes only):

    True or False​

    (Justify if False)​

    1. The jumper, when set for 110v, covers both the "230V" and the "115V" tines (as shown in the picture below).

    2. Likewise, when the jumper is set for 220v, covers both the "230V" and the "3" tines (as shown in the picture below).

    Picture below: ImageShack® - Online Photo and Video Hosting

    THANK YOU! :ninja:
  20. davidprice


    Jan 1, 2005
    TRUE (or, at least, that worked for me :ninja:)