One side stopped workig on my 2600 amp, so i am running thru center out put. now sound fades up and down.

Unfortunatly, there could be a few different causes for this and without the amp in frony of me it would be impossible to diagnose it. The best bet would be to have a qualified repairman look at it. Here is a link to the Peavey Contact page which has a link to their service centers.
Peavey com

Hello,

Check the "BRIDGE" switch position, "IN" for "BRIDGE", "OUT" for "STEREO", and clean ALL back switches with a cleaning spray and then run the amp again, also check the two green lights activation at front, if they activate, then amp is certainly working, let me know further.

sounds like your cooling fans may not be working properly. Feel the bottom of the amp to check for forced air from the fans. Amps will over heat very quickly once the fans burn out..Hope this helps shannon

Please add more background, which channel stop working?
As a blind advice, try to clean ALL back switches, including Stereo/Bridge Switch, let me know your results.

The SP2 speakers are rated at 1000 watts PROGRAM which is around 500 watts RMS MAXIMUM. You should be using an amp capable of a maximum of 500 watts a side... Your amp is WAY too big. You will have to throttle it down. The speakers have the protection for the tweeters but NOT for the woofers. At five hundred watts RMS and 8 ohms the current is: P = I^2 * R so I^2 = 500/8 = 62.5 so MAX current is 7.9 amps. I recommend you put a 8 amp FAST BLOW fuse in the speaker leads. If the fuse blows, you have saved another speaker and you are DRIVING them too hard. For greater safety make the fuse a 7.5 amp fast blow. Also get a sound meter. The max on these speakers is 125 Db at a meter distance... and in your venue you should NOT exceed 100 Db to be safe with the OSHA regulations regarding hearing protection... I suspect you are driving the speakers too hard. One side may be getting more bass. The speakers are rated down to 55 Hz. DO NOT boost bass up as you will overheat the speakers. If you are using microphones, be careful of feedback, especially that above hearing range. If you need real low bass, then get an 18 inch subwoofer. No matter, stay within safe sound levels to avoid lawsuits and hearing loss... I know several deaf musicians...

You would send high as well as low to the sub and unless the sub had a built in crossover it COULD get muddy sounding. The specs SEEM to indicate the 118 DOES have a low frequency crossover so it SHOULD be OK... How would it sound? An 18 inch sub normally adds to the sound of a system... You MAY need to PAN over to send more power to the one side with the extra load on one side. Often people use two sub's... one for each side so it is balanced.

Brand new? Take it for warranty repair IMMEDIATELY... don't mess with it !!!

The only thing for you to check is that you did not turn on "STANDBY" as this shuts down the power amp and the capacitors will bleed off and sound will fade. Try switch in both states before complaining

ONLY use the amp in STANDBY for a brief period (20 seconds) to let the tubes warm up... Leaving in STANDBY for a long period straains the input filter capacitor. If you are done with using the amp, turn it off...

It should be able to do this. You would need to put each type speaker on a seperate side and then use either an elctronic crossover or an EQ set to pass only lows into the side for the subwoofer to block sending highs to the subs.

Hi there,
you can run one amp from the main out puts and the second amp from the CTRL Room out puts. The CTRL ROOM are outputs that are linked to the same bus as the master fader. This will work fine...
Best of luck

One side of the amp has failed and repair is NOT DIY. Take it in for servicing. This amp has many components in the power amp and repair is complicated. A failure can lead to 20 components being damaged. Failure to replace all damaged ones can result in immediate failure destroying the replaced ones.