SLT: I asume you are talking about the -200.
I was on the -300/-400, mostly -400 and we used bleeds and packs on for every takeoff. The only time I had the bleeds off was when departing from Canada, on a short rwy over the Atlantic, and then we used the engines bleeds off and the APU to power the left pack. (The X-Bleed was then off, and after T/O we put the R Eng Bleed on with the R pack, APU off, L bleed on). Therefore we were never unpressurized during this procedure.
It is in the Boeing manual.
Regards