I haven't had much experience with tube amps and was wondering something.

Say that I have a tube amp that has a Pre Gain and a Post Gain knob. If I crank the Pre Gain does this mean I've over driven then amp or do I need to crank the Post Gain knob?
ive seen that on peavey's the pre gain is the gain and the post gain is just volume. so just crank the pre for gain and adjust the post for volume.
When the Power of Love overcomes the Love of Power, the world will know Peace.-James Marshall Hendrix
I think the pre-gain is just how much gain you want, but it do gives more volume. but then you use the post gain to get the volume you want?
Yeah, I know what the knobs are for but I want the tubes to be saturated so I get a better tone from them. So to do this do I have to crank the Post Gain/Master Volume knob?
crank the pre gain for more dirt in general

if you can take the loudness crank the post gain as well for some power tube distortion happening as well
The pre overdrives the preamp tubes by raising the volume, and the post cranks the powertubes by raising the volume.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
Another question...

Can the tubes be overdriven by a distortion pedal also or does it have to be an OD? Currently I have a DS-1 and was wondering if that would do the trick for a tube amp or if I would need to get maybe a TubeScreamer.
It depends on the pedal but some distorion pedals can work rather well at overdrivey sound and as a boost for an amp.

Turn the distortion/drive down low, turn the level/volume up.