There were some very specific and hard to find gear requirements - off of the top of my head (not looking at the gear rider) I think it was mainly a Hammond B3. A real one.. with a Leslie rotating speaker (f**king fragile nightmare to transport and make sure it works)..... s**t that was used back in the 70's/ (think Deep Purple key sound). The Leslie has a motor and belt that actually spins two speakers mounted at 180 degrees from each other (looking down, picture the shape of an hourglass) which rotate towards the mic.. makes a specific sound .
It can be replicated with digital keys, and LIVE you would NEVER hear a difference.. hell, even in the studio with the right EQ's and tube preamps, it might be hard to discern the difference..
anyway - from a non keyboard tech - that is part of what I remember...
