1988 G-K 800RB Blows fuses !

Variac at zero.

https://medias.audiofanzine.com/files/800rb-service-manual-472053.pdf

You gotta take it in.

 

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.

 

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.

 

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.

 

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.

 

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.

 

No offense, but if you have to ask how to trouble shoot, you have no business being inside.

 

It's also not particularly easy to work on.

 

Yep, send it to me! Have repaired dozens, cool amp.

 

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!

 

I have seen far more damage upon failure, hence my caution.

 

I'll give you $50 for it.

 

That baby is super clean it looks unused

 

Yep, like I said, I have repaired many. There is many

Of course you have.

 

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

 

It wasn't a transformer problem with the GK. Quite rare to see a transformer fail.

 

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.

 

Were you blowing up the 800s because you were running them with a 2ohm load?