I get a hybrid, Geddy/Squire sound through my gear. I am 41 and started playing when I was 15 and was influenced mainly by Geddy, Chris Squire and John Paul Jones. So I spent many years learning Rush, Yes and Zep tunes and 90% of the time bumming that I never sounded like any of these guys. I always assumed it was because I was playing a P-Bass through a Peavey TNT 130 (solid state/NO TUBES), and just wrote it off to having the wrong gear. I thought I needed a Rickenbacker 4001 - run stereo, Sunn Amps (+ a Marshall for distortion) - I did end up getting a Rick - but not the rest - never got Geddy or Squire...
In hindsight, I realize that I new NOTHING about my bass, my amp, tone settings, compression, NOTHING... So I may have been able to dial in a tone through the amp that approximated the toothy Geddy/Squire thing - but I just don't know.
Today I have a Fender Jazz V (passive) and a MusicMan StingRay 5 (Active) and I play through an Ampeg SVT II PRO and SVT810e.
Almost without trying, I get much closer to the Geddy/Squire tone - especially when I play my Jazz. If I want more Geddy, I play fingerstyle and dig in hard. I usually favor the neck pickup, but have both almost dialed up full. Roundwound strings and a goodly amount of compression, tone up almost full = pretty close to Geddy - and I am not even really trying to get that sound - it's just the sound that this rig, bass and playing technique generate, which seems to echo what many are saying.
I have the drive on the Ampeg up at about 12 o'clock so I get a lot of nice tube warmth and grit, the rest of the pre-amp tone knobs are at 12 noon too. I boost the Graphic EQ at 180hz about 2db...
If I pull out a pick, Chris Squire shows up. If I play with the pick up near the neck, I get the fat, Squire sound like on "Long Distance Runaround" in the middle section - "I still remember the dream there..." - if I dig in near the bridge, I get the toothy snarl like the beginning of "L D Runaround" or the intro of "Roundabout".
Mind you, I cannot play like Geddy or Squire, but I do end up inadvertently, through nurture, nature and serendipitous gear acquisition doing a pretty fair imitation of their tone.
To sum it up:
Ampeg SVT II PRO - all dials at noon (not counting gain and master volume), Graphic EQ bumped at 180
Ampeg SVT810e
Fender Jazz V or EBMMSR5 + roundwounds
Finger Style + dig in (and years of listening and being both overtly and subliminally influenced by Geddy Lee and Chris Squire)
Oh yeah, playing at a nice, beefy volume sure doesn't hurt things any!