Ampeg V4BH - Bursts of Power

I've been running my Ampeg V4BH as my primary amp coupled with my Ampeg Gene Simmons 2x15 cab for close to a year now, and lately it has really been surprising me. When I get to a gig, I set my rig up and I will put it in standby mode to let the tubes warm up for about ten minutes before we start. When I take it out of standby - every once in a while the amp just sounds like GOD. It really sounds more like an SVT than a V4BH. Compared to how it normally sounds - the volume is insanely loud, and the tone is thicker and even ballsier. Sometimes it stays like this for a song or two, sometimes it only lasts a few seconds before fading back to "normal". When it acts like this - it's like a race car that just took a hit of Nitrous.

I'm running the original stock Sovtek tubes (2002-ish) and everything else about the amp other than the faceplate is bone stock. Anything that might account for these momentary bursts of power? Usually when I've had components go bad in an amp or the bias drifts, the sound and volume are deteriorated. This is quite the opposite. Just hoping the amp isn't going "Supernova" before it dies...

 

Update: Problem solved. I had been using a 1/4 adapter from the preamp out to an XLR cable running to the snake to main. This seemed to be draining almost half the power fromt he V4BH. I would normally run the balanced XLR out, but it had been cutting in and out so I just used an adpater on the 1/4". I unplugged the adapter, and bam- there was the magically loud sound. We ran a dedicated direct box between the preamp out and the XLR to snake and the problem is solved. I'm guessing there was an impedance mismatch with the plain Jane adpater I was using.