Fluctuations of the loudness of speakers???

Cables are all brand new but the tube does apply since I have Musical Fidelity Nu Vista amplifier that supposedly contains some tubes. I wouldn't even know how to go about getting let alone replacing one...

most likely the amp

Do you guys think a bad tube would probably be responsible for the volume fluctuations rather than an occasional "crackling" sound? With rock music hard to notice, but put on some ambient music, and it's more noticable...thanks everybody for their (even future) inputs and ideas.

Most likely a bad tube but could be a bad solder joint on the output stage.

Re E-Mail, you can just reverse the speakers by reversing cable from left to right speaker and right to left. If the problem is still anchored to the same speaker then its not a bad tube. BTW, I've never experienced fluctuating volume from a bad tube, but that doesn't mean the problem is not in your amp or in a source. If you can, change sources and see if the problem goes away.

Also, are you detecting a shift in the stereo image toward the same speaker when the volume fluctuates, or does it stay centered. If it stays centered then the problem is not likely to be from speakers or, if you have two or more tubes, one for each channel, is it not likely to sourced to a tube. Its to coincidental to have two tubes failing at exctly the same time.

Hope that helps a bit.