Hi,
If you have no Idea what they sound like, then why exactly are you looking for a "tube pedal" ?
Don't buy a piece of gear just because it has a light-glowing bulb in it. Don't get me wrong, I love tube amps, but what you are looking for might be a solid state distortion pedal like
a Proco RAT maybe ? Or some of the Boss pedals. They don't have toobz in'm but they are quite useful to get a heavy guitar sound. I suggest you go try them out in a music store and make your conclusion.
Also, note that every part in the signal chain affects your tone, for example, my guitar with that effect on that amp probably sounds different than yours, maybe what you need is a nice pair of humbuckers, or a new amp. What's your setup ?
If you're looking for an effect, your not gonna make it too easy by narrowing your search down to tube pedals.
And btw, doesn't this belong in the guitar section ?
good luck, Arno