Question about GK800RB

[touchdown!]

The following was posted as a description on a craigslist ad:

Bi-amped for up to 400W of power (low amp delivers 300W to 4ohms or 200W to 8ohms, hi amp delivers 100W to 8ohms)

Not being entirely familiar with Biamping, I have a question; could I simultaneously run a 4 ohm cab (1x18") and an 8 ohm cab (4x10) with this amp? I would venture to guess that it is a no, but it would be perfect if it was the case, so I figured I would ask.

 

[jady]

That's a big negative brother unless you want the 4x10 to only have highs and be half as loud. I am not feeling comfortable with the ohm mismatch either but I am not 100% sure.

 

[shoot-r]

Touchdown, You can run your 4 ohm 1-18" cab from the 300 watt 4 ohm out and your 8 ohm 4-10 from the 100 watt 8 ohm out. You can run it like this either full range or push in the bi-amp switch and run it in bi-amp. You can then adjust the levels of each speaker cab using the master for each amp. You CAN'T run both of your cabs from one output.
I run my GK 800 full range (from the 300 watt 4 ohm out) into a 4 ohm Eden 212XLT. I've had great luck with the GK 800. Been using this same head since it was new in 1984.

 

[SERPENT865]

I wouldnt do it either.

 

[scuz]

Here is the REAL answer:

Touchdown, You can run your 4 ohm 1-18" cab from the 300 watt 4 ohm out and your 8 ohm 4-10 from the 100 watt 8 ohm out. You can run it like this either full range or push in the bi-amp switch and run it in bi-amp. You can then adjust the levels of each speaker cab using the master for each amp. You CAN'T run both of your cabs from one output.
I run my GK 800 full range (from the 300 watt 4 ohm out) into a 4 ohm Eden 212XLT. I've had great luck with the GK 800. Been using this same head since it was new in 1984.

It's a great amp and I can't wait to get an 8ohm 2x10 to compliment my 4ohm 1x18.

 

[monkeyland]

the standard wisdom as it pertains to cabinets and impedance doesn't apply to the 800rb because it uses two separate power amps. now if you try to run that load off of the 300w output then you would have trouble.

 

[scuz]

[Invalid or Expired Link Removed] view of the back panel will shed light on things. Lookit the far right of the picture.

 

[Standalone]

The Hi power amp is 100 watts into 8 ohm, 60 into 16 ohm. The Lo amp is 300 into 4, and 200 into 8. So your cabs are 100% ideal, especially if you set the crossover to best take advantage of the strengths of each cab-- I would think that this would mean setting it fairly low.

[Invalid or Expired Link Removed]

 

[BassMonstrum]

I have another question about the GK800rb:

When mounting it in a rack is it wise to have an open space above it for ventilating purposes? It seems to me that it is 3 rack-units tall, so is it best to have it in a 4U-rack?

 

[BillyRay]

Absolutely. It was probably designed to do just that: other companies, Peavey notably, were getting into the full range, multi driver craze in the 80's. This usually meant that the cabs needed to have a passive crossover built-in.

Mr Krueger never liked passive crossovers, so the 800RB is his answer to Peavey's 1820, 3620, etc. You could take any cab, set the crossover point yourself and power two different boxes from two different sources. In theory, it's a win-win situation: you don't waste power on a cab that doesn't need much of it (a bright box or a small enclosure for midrange drivers) while getting a lot of watts to the subwoofers PLUS you can use whatever cab you fancy.

Now the crossover freq. on the dial are not really in the best possible bandwith for a two-way system, but the concept (and tone) were still huge.

 

[Standalone]

I have another question about the GK800rb:

When mounting it in a rack is it wise to have an open space above it for ventilating purposes? It seems to me that it is 3 rack-units tall, so is it best to have it in a 4U-rack?

I just got a deal on one at a local Sam Ash, with what appears to be a custom 3 space. The rack looks to be about the same vintage as the amp, so for what that's worth, it is a sign that top ventilation may be unneccesary.

I played around with it for half an hour or so in my studio, ambient temp 78 F, running it full range to various single 4 ohm cabs at medium, low and --for brief spurts-- wide open just to put it through its paces. I felt the fins on the back when I shut down, and they were barely warmed at all, as in only warm enough to not feel like cold metal.

I'm only going to be concerned in direct sunlight, I think.