Do i need to mic or not?

How big would a gig have to be before i would have to mic my amp. My amp is like 80 watts, and it is tube.(Peavey bandit)

generally when you gig you will find (well this is my experience) that the venue generally has some p.a equipment (can be very bad!) so you should be alright for most occasions anyway. an if there is no micin up of your amp then as an 80 watt full tube amp is deafingly loud it generally can stand up in most small to medium sized rooms. but make sure you get it off the floor as this will mean that the sound comin out will be headed more directly for peoples heads. it also sounds better then.

If you have to do a stadium or auditorium, mic it. Smaller gigs it's best to do what the house wants (if they have a pa). Some places don't care if you just play straight out, but if you're playing at like a college event or a 'battle of the bands' they're probably going to mic it or force it through their system one way or another so they have control of the volume

ok but does it sound jsut as good if you mic it, also if im playing live im jsut gonna run my amp and everything to the main pa speakers, would that work also??

That depends on a lot of stuff. If you run everything through the pa that does what putting a mic on it is for. I don't think it would make sense both plugging into the pa and putting a mic on the same amp. Generally it's a good idea to go through the pa but if your amp doesn't have an output jack that sounds good then you'll be putting a mic on it or playing straight out.

As always, depends on your equipment and the venue.