I have a 14 watt CFL ballast that came from a broken CFL (which I didn't break), and I was wondering about this, would the ballast work on a single F14 T8 or a F14 T12 fluorescent tube? Or would it overdrive the tube? Because the ballast is 14 watt.

https://www.lighting-gallery.net/gallery/displayimage.php?album=lastup&cat=12246&pos=0&pid=154620

It will work just fine. I used to do this all the time and never had any issues. In fact, I would buy CFLs just to use the ballasts with linear lamps.

Maybe the power won't be correct (the lamp will be very likely underdriven), but the thick lamps are fobust against that and do not loose that much performance.
 So beside of the lower output, it should indeed run fine.

Ok, thanks. I'll try it soon.

O wow I never thought of this! Aren't most quality CFL bulbs program start? That would make them easy on lamps then eh? Hmm...

IDK, I might try it though.

That is a pretty smart idea though, I never thought about doing that.

O wow I never thought of this! Aren't most quality CFL bulbs program start? That would make them easy on lamps then eh? Hmm...

The better ones use just simple PTC based preheat timing, which needs to exactly match the tube characteristics (the filament mass and resistance,...)
But when powering some beefier lamp (the case for the T8 and 12),the preheating becomes not sufficient, plus because the thicker lamps ignite at lower voltages than the thin spiral, the ballast effectively becomes an IS.
Plus the beefier filaments of the thick lamp wont be able to protect the ballast in case of the cathodes loosing emission, so you have to be cautious when turning ON the lamp - in case it behaves suspicious, better to switch it off immediately, before the transistors fail (you have few seco ds window for that).
Otherwise if the lamp is good, it runs fine.
On the other hand these ballasts should be readily available (from burned out CFLs, many of them have really just burned out tube), so no big deal rep,acing it once it fails. You dont have to  are that much about the power rating - anything from 10 to 18W rating will work fine with both 14 and 15W.

Wait, the transistors can fail, if not turned on properly? Well than that case, I may have to do this experiment outside, incase if it explodes. :|

It won't explode. It'll just smell bad.

The transistors don't contains flammable materials that can explode, but they can be overheat and fail with or without arcing.

Wait, the transistors can fail, if not turned on properly? Well than that case, I may have to do this experiment outside, incase if it explodes. :|

If the lamp has too high arc voltage drop ( mainly because of the consumed emission material from the cathodes and/or seal failure), the transistors overheat, which turns the silicon into a non controllable conductor. And this causes a short circuit.
This may happen (and does happen in very significant part of the failed CFLs), so the ballast is supposed to be designed to fail safely.
That means mainly the presence of a proper fuse (and/or fusible resistor) in one of the input leads and a ballast box ( CFL base; any electrical rated box will do well) to contain the eventual capacitor explosion (a failure mode often present with even larger capacitors in modern TVs and no problem from that beside the thing not working).
If you would be concerned about safety with these, way worse are many coil and core ballasts, which can turn into very hot iron brick capable to cause fire and emitting noxious smoke even few minutes after switching their power off.
This electronic just pops, maybe triggers the mains breaker and all the "show" is over...