[font=trebuchet ms]A 4 string bass is like a big guitar with the high B and E strings removed, and everything else tuned down a full octave. So the scales, positions and notes are all the same, just down an octave, and you're missing a couple of strings.

Any amplifier should work just fine, as long as it doesn't have some kind of low-cut filter to keep out bass frequencies. I have never heard of an amp that had such a filter, but you never know...

The speakers may be an issue only if they weren't designed to handle the lower frequencies produced by a bass. As I said in an earlier post, you need a lot of power to produce decent SPL at bass frequencies, so your speakers will be driven hard. A speaker that is rated down to 40 Hz at full power is good to go. Otherwise, you will need to get something that will do the job.

And do your tone a favour. Don't get a cab with a horn or a tweeter in it! Tweeters sound good in stereo systems. Horns sound harsh anywhere! They both sound just plain horrible in bass or guitar rigs. My opinion, but I ain't humble about it! For good bass sound, you want sealed-back cabs with speakers in 'em.[/font]