I was just wondering - if I were to have a bass cab stack, and i were to use lets say for example a small Fender rumble amp as a head , would this be possible ? As in use a small combo amp as the head to a stack ?
nope, can't happen.. You need a head to act as a head.

with enough wiring messing around you probably could use the fender rumble with an external cab but it would be pointless because it's still only like 15 watts. More speakers/bigger speakers do not make it louder, they just change the tone and stuff like that.

also, there's really no need to have a stack unless you're playing really big gigs. get a really nice ampeg combo for bass. that's what my bassist has. it's sweet
My Guitars:
Gibson Les Paul Studio
Epiphone AJ
Ibanez Strat Copy

Orange Tiny Terror Head
Old beaten up Peavey cab
Marshall MG30DFX
does it put out sufficient wattages? a normal output won't work unless it's powered (it should be labeled 4 or 8 ohms [the omega symbol]). if you're going to be dropping some cash on new amps, however, i'd nix the fender rumble and get a decent GK or a low end Ampeg. they may not be cabinets but they're damn good combos and plenty loud.
Phish Phan
If there's a jam out there, I'm probably listening to it.

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No guys i don't have a rumble i was saying an example, i have a 200 dollar GK and i really like the sound and im so used to it and around it i just don't want to get a new head an be in a different world... Well thanks anyways =\