Depends on the distance between your components. I wouldn't place the power amp on the one stand with small signal components because there is a possibility of induction of parasite currents if the power transformers aren't shielded well. It may cause hum. Simply saying power amp should stay away from other components and certainly have much more room for heat dissipation. If your stand has large enough space(so that preamp is above at least by 4" from power amp)it maybe OK.
component order on a rack?
Alright I want to make sure I am not overlooking what is the obvious to so many others, but is there a "best" order for placing audio separates on a rack. I have five shelves. It is a Michael Greene rack I recently got used. I was planning on putting my turnatble on top, tuner next, cd player, preamp, amplifier. Is this the best? I trying to do things right so any advise would be helpful.