Sample an 808 kick
sample the one off "terrorist" by ray keith
use a sine wave (any synth has one for an oscillator)
that's most of the oldskool basses down to a T
I think the problem with people trying to make oldskool is they try too hard. It's really easy to do.
Oldskool is all about "that" sound. To get the sound you nick it like the original producers did. They used sampled breaks and hooks, then the synths can be used for shit like pure sine waves and strings and floaty synths and FX.
Also don't fall into the trap of cutting your beats into tiny bits, you'll lose the flow. Listen to old tunes, do you hear perfect beats? no! so think simple. check Krust's "set speed" it's pretty much a break looped with an 808 kick playing a little tune. Must have taken about an hour to write but it's still dope.
If you try too hard and piss about too much you'll fuck up the sound.