GK 800RB question trouble shooting

helenforsdale · #1 12-05-2012, 02:20 PM

Hey folk…

Quick question - I've got an 800RB that's not working well. The 300Watt/4ohm out is fine, but the 100watt, 8ohm doesn't work.

Any clues as to why this would be? And is this a simple/cheap repair? I'm afraid the repair might cost more than the thing is worth…might be better just to get another one.

Thoughts/opinions/help much obliged.

husky123 · #2 12-05-2012, 02:50 PM

Hey there. Unfortunately this happens a lot with the 800RB's. The "high" amp is 100W at 8 ohms. Sometimes people will accidently (or just not know) plug a 4 ohm cab into that jack. Poof, amp fried.

I keep that sucker covered with a small piece of duct tape unless I'm biamping (which is rare).

will33 · #3 12-05-2012, 03:04 PM

Quote:

Originally Posted by husky123

Hey there. Unfortunately this happens a lot with the 800RB's. The "high" amp is 100W at 8 ohms. Sometimes people will accidently (or just not know) plug a 4 ohm cab into that jack. Poof, amp fried.

I keep that sucker covered with a small piece of duct tape unless I'm biamping (which is rare).

This is a common issue. ^^

Fortunately, the output transistors and related parts are not expensive. If you can manage to verify blown outputs are indeed the problem, and you can do the work yourself, can get it running again for a good bit less than $100.

I think I added up about $150 in parts to re-do the whole output section of my 800rb IIRC. Haven't done it yet, but I remember being able to do both power sections and re-cap the supply for something around $200, getting all the parts at retail and doing the replacement myself.

I could dig up more info and schematics and stuff from a real computer later....on a phone here, although I can email you pdf attachments of the service instructions, schematics, etc. PM me for that.

helenforsdale · #4 12-05-2012, 03:19 PM

Whew, that's good to know that it's not a major issue. I would never use the 8ohm out, but I don't want it to affect the over all sound/quality of the amp.

And yeah - I can't do repair work - I'd have no idea what to do. I know some people tho...

dhsierra1 · #5 12-05-2012, 03:28 PM

I had a local amp tech repair a burned out (literally) 100 watt board for just over 100 clams, worth it since I plan on running a third 15" out of it (full range) for outdoor gigs.

That it's kaput, though, shouldn't affect the overall tone.

helenforsdale · #6 12-05-2012, 03:29 PM

One last question -

Do years matter on these things? Are ones from the 80s any better than the more recent models?

will33 · #7 12-05-2012, 03:59 PM

Quote:

Originally Posted by helenforsdale

One last question -

Do years matter on these things? Are ones from the 80s any better than the more recent models?

Some purists might think so, I don't. They stayed pretty consistent with the circuit over the years and kept the same sound. The only changes made were replace some littke parts that may've went obsolete and the change to toroid transformers in '96. Mine is an '89 but the newer ones sound good to me too.

And yes, shouldn't hurt anything just using the 300 watt amp. May not be a bad idea to disconnect the 100 watt amp from the power supply but I don't know that it's necessary.

helenforsdale · #8 12-05-2012, 04:15 PM

Thanks man, much obliged. Pretty sure this is an early one as it only seems to have one LED, not two.

Quote:

Originally Posted by will33

Some purists might think so, I don't. They stayed pretty consistent with the circuit over the years and kept the same sound. The only changes made were replace some littke parts that may've went obsolete and the change to toroid transformers in '96. Mine is an '89 but the newer ones sound good to me too.

And yes, shouldn't hurt anything just using the 300 watt amp. May not be a bad idea to disconnect the 100 watt amp from the power supply but I don't know that it's necessary.

will33 · #9 12-05-2012, 04:24 PM

In the early models will have their power switch mounted horizontally. You switch it left to right instead of up and down.

If yours hasn't come off over the years, it will have a sticker on the back by where the power cord goes in that has the date it was made. Mine says 3-89, for March of 1989.

helenforsdale · #10 12-05-2012, 04:45 PM

Yeah, this is horizontal - no sticker. Definitely early years tho - that's for sure. Cleaned up, I'm hoping this thing'll slay...

Quote:

Originally Posted by will33

In the early models will have their power switch mounted horizontally. You switch it left to right instead of up and down.

If yours hasn't come off over the years, it will have a sticker on the back by where the power cord goes in that has the date it was made. Mine says 3-89, for March of 1989.

will33 · #11 12-05-2012, 04:56 PM

It will slay....

Turn the gain up to at least noon-1:00. Use the boost for overall aggressiveness and the master for overall volume.

husky123 · #12 12-05-2012, 06:56 PM

I'm with will on this one. I've had a few of each over the years and really don't hear a difference. They all just sound gooooooood.

Wally Malone · #13 12-07-2012, 08:53 PM

Quote:

Originally Posted by dhsierra1

I had a local amp tech repair a burned out (literally) 100 watt board for just over 100 clams, worth it since I plan on running a third 15" out of it (full range) for outdoor gigs.

That it's kaput, though, shouldn't affect the overall tone.

I did a gig some years ago at the Santa Cruz Boardwalk with Bo Diddley using three cabs through my 800RB. I used two Hartke 410s and a Hartke 15. I put the 15 into the 100 watt section since it was the lowest rated cabinet and used full range. I still remember how good my bass sounded at that gig. It was an unusual night being as the temperature was still almost 90 degrees early evening. It was one of the gigs where everything just went right.

Wally