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1988 G-K 800RB Blows fuses !

Ashtray666

Ashtray666

Sep 9, 2018
39
23
Orange County
#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:

image.jpg

image.jpg

image.jpg

image.jpg
 
#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
Ashtray666 said:
@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.
Click to expand...

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.
 
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#7
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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#12
Ashtray666 said:
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:

View attachment 3223118
View attachment 3223119
View attachment 3223121
View attachment 3223120
Click to expand...
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!
 
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#17
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
 
#19
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.
 

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