So, I just received my first Tube Amp ever by mail (ordered it online, got it today), and it's a real killer! 20W of pure tone, right in my music-room. However, I have a couple of questions, since I've never owned a Tube Amp before.

1: What exactly is the Effects Loop? I've noticed that my TC Corona Chorus sounds beautiful when placed in the Effects Loop, but becomes inaudible when placed before the Input jack. How come that is the case?

2: How long life span should I expect from the stock Tubes? And after that, how often should they be changed for best tone?

3: How do I tell if a Tube is about to "die"?

I realize that these may be rather basic questions, but this is the first time I own anything Tube-driven. I only know how they work, not all the actual need-to-know stuff... Any help is greatly appreciated :)