I've been reading through HC to see what people say about the boss turbo OD. 2 things that surprised me in general, not just limited to the Turbo.

1. that overdrive pedals aren't the best for metal (death, thrath)
2. that people will combine an od pedal with a distortion

what is the difference between od and distortion (on a tube amp)?
distortion basically is designed to create a distorted/fuzzy sound, whereas OD's act mroe as booster pedals and are often used to boost the distortion on a valve amp. So i u need to add abit of kick to ure Distortion pedal, u whack an OD infront of it.
For a tube amp, most people will use an overdrive pedal.

Using a distortion pedal will mask the tone of the tube amp, and have the distortion pedal take over.

To get into higher gain territory, tube amp owners will kick on an overdrive pedal infront of the overdrive channel of a tube amp, getting even more gain.

IMO, with a few lower gain distortion pedals, you'd be better off getting an overdrive pedal only for your tube amp.
so does that mean you shouldnt use a dist. pedal infront of your tubes, or you just shouldnt, cuz i know some greats who do.
Vai uses a DS-1 infront of his tube amp as a boost, but due to its low gain nature, the DS-1 is more like an overdrive anyway.

For the most part, people will stay away from high gain distortion pedals on tube amps, unless if they want a completely new tone all together. If all you want to do is add gain while maintaining the tube tone, than an overdrive is the way to go.
ok, so what about an od pedal with the od channel on a tube amp, or is that where od pedals should be used?

and what would be a good dist pedal for a tube? and what the heck is this?