Ok, Basically what I want to know is: Can one run a tube amp head, say for example a 5150 through a solid state combo amp's speakers (such as a Fender 212R 2x12") and save buying a cab?

Probs a stupid question but yeh, need ta know.
You probably could but you'll probably end up blowing something up, and if not having a rubbish tone.

Epiphone Les Paul Standard w/ SD Alnico Pro II's
Fender Aerodyne Telecaster & Stratocaster
Marshall JCM 800 4104 combo

E-Married to Funny_Page
if the ohm of the speakers in the fender match that of the head it can easily be done. all you'd need is a speaker cable, some speaker wire and a 1/4" mono jack.
i used to be a mod, then i took an arrow in the knee.
Ahk, sweet, would it be worth it though you reckon? like any drawbacks for sure? (tone etc as said)
It will work out fine as long as you match the ohms and make sure the wattage handling of the speakers are up to par.

Only real down falls are... It will not sound as good as a cab because most combos are open back so if your playing metal that will pose an issue. And the speakers are voiced for a Fender SS amp not a 120 watt tube metal beast.

Example of what it would look like.... Added the option on to my Ampeg combo....
nice, thanks man, helped me out with some good info. I'll probably just end up getting a cab, keep it simple now i know. But yeah, thanks.