1988 G-K 800RB Blows fuses !

Discussion in 'Amps and Cabs [BG]' started by Ashtray666, Nov 22, 2018.

  1. Hello hello,

    Ive got here a Gallien-krueger 800RB Bass amplifier I bought from my local pawn shop. It was non-functional but the guy said I could take it for $40 cash. no tax. This thing did not even have a sctratch on it!! So, I took a chance and bought it. I was not allowed to open it in the store so I ran home to begin surgery.

    Inside is perfect. (photos attached). Way too clean looking. Maybe somethings have been replaced already? I do see ‘87’ and ‘88’ on lots of parts.

    My question is, Is an oscilloscope necessary to test the amp or components or can I with just my multimeter do enough? So far all I can think of is to test the output transistors.. I really dont want to take this one into shop quite yet (I’ve got my 400b in a shop because it got french fried). But, I am also not going to attempt anything beyond my capabilities. So if I gotta take it in, I gotta take it in. Just figured I’d try to learn more about bass amps.

    Here’s some photos:

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  2. Mingo Sanders

    Mingo Sanders

    Mar 11, 2008
    Austin, TX
    Ashtray666 likes this.
  3. @Mingo Sanders


    Damn damn damn, You’re right.

    But hey I’ve been looking for the service manual Just to have, so thanks for the link. Suppose i’ll just trade off when the other is ready. It’s been in since September.. I’ve had to use my svt4pro & 8x10 for every gig and it’s killing me haha.
     
  4. joel406

    joel406 Inactive

    Dec 27, 2013
    Florida
    Having owned one of these before I would be the first to tell you that getting it fixed and running at 100% is worth it. There is no finer sounding amp than that baby right there.
     
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  5. That’s a fine, clean looking rig.

    As to your oscilloscope question...
    First a big fat caution...
    That question in an of itself has inexperienced electronics newby written all over it.
    Before you jump in, how about you give us some info about your electronics background when it comes to repair and diagnosis. If we’re going to help, we need to know at what point you might get in over your head.
    Stuff like this can be dangerous for those with little/no experience.
    The first order of business is to be sure you don’t misinterpret some advice and get yourself into trouble or get hurt.

    But I will say, that an oscilloscope is not usually the first go-to piece of equipment used in amp repair, especially one that is stone cold dead. Probably 95% of amp repairs never see the scope come out.

    So let’s approach this safely and with reason. Or try to determine if you’re better off to have a qualified tech look at it for you. The only thing you should be frying today is a very large bird.
     
  6. Roland GR 88

    Roland GR 88 Commercial User

    Sep 16, 2013
    Ontario Canada
    Retail store manager
    I'd say that if you've already 'french fried' a 400b then cut your losses and have a tech look at this one too.
    One of the most important things one can learn here about bass amps is to take the advice of the few techs that populate this site.
     
  7. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    No tech wants to repair something that has been attempted by somebody who doesn't know what they are doing. Many will charge more, or simply refuse to work on it.

    If you don't know what you are doing, find a qualified tech who does.
     
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  8. Mvilmany

    Mvilmany

    Mar 13, 2013
    Upstate NY
    As an owner of an identical 800 RB, which has been my main head for 20 years, I'm going to say to get it repaired by a tech.
     
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  9. Jim C

    Jim C I believe in the trilogy; Fender, Stingray, + G&L Supporting Member

    Nov 29, 2008
    Bethesda, MD
    No offense, but if you have to ask how to trouble shoot, you have no business being inside.
     
    Last edited: Nov 22, 2018
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  10. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    It's also not particularly easy to work on.
     
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  11. Hand slap

    Hand slap

    Feb 14, 2016
    Yep, send it to me! Have repaired dozens, cool amp.
     
    SirMjac28 likes this.
  12. Hand slap

    Hand slap

    Feb 14, 2016
    I have found only 1 bad output on that model, many times, checked the associated components, worked well, adjust bias. Hopefully it’s a great buy for you!
     
    EatS1stBassist and SirMjac28 like this.
  13. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I have seen far more damage upon failure, hence my caution.
     
  14. Thumpin6string

    Thumpin6string Supporting Member

    Apr 25, 2013
    Shoals Indiana
    I'll give you $50 for it.:D
     
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  15. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion

    Aug 25, 2010
    The Great Midwest
    That baby is super clean it looks unused
     
  16. Hand slap

    Hand slap

    Feb 14, 2016
    Yep, like I said, I have repaired many. There is many
    Of course you have.
     
  17. DownhillWillie

    DownhillWillie

    May 22, 2007
    when this model came out I heard a band in LA "Bang Tango" using one and had to have that sound!
    I agree the take on this head is really really good, Sound wise. It is there that all the goodness ends.
    I had a deal with GK just so I could use these heads. They blew up regularly, I was walking into GC with no questions asked and dropping off my blown heads and leaving with a new one's monthly. So often that I was on a first name basis with one of their VP's. He finally told me that the problem was in order to accommodate the small compact size of the head that the power transformer used was unable to handle the load or demands placed on it. I do believe they did finally get that worked out well down the road. I had to abandon the use of it in the mean time for something more reliable. But damn did I love that head. Similar story with Mesa Titans, God they IMO, were the best sounding heads I ever heard, but I kept blowing them up as well at 2ohms...
    Bare in mind that was 80's technology, I'm sure there's a solve out there by now right? Good Luck with it, if you ever get past the issues you'll love the tone outa 'em
     
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    It wasn't a transformer problem with the GK. Quite rare to see a transformer fail.
     
  19. DownhillWillie

    DownhillWillie

    May 22, 2007
    That makes me wonder then what it was, Because it was a constant problem and that is what they told me after a lot of inquiry.
    Now I'm really interested in what the heck it actually was that caused this! Having zero knowledge of electronics I'm forced to rely on what I'm told.
     
  20. Kro

    Kro

    May 7, 2003
    New Jersey
    Were you blowing up the 800s because you were running them with a 2ohm load?