I have to echo the same concern about attic vs outdoor mounting. If you can not or will not consider outdoor mounting, you have little hope of reliable reception.
The signal from WPVI on real CH-6 would no doubt require a large deep fringe all channel antenna such as the Winegard HD7084P... Or a combination of cut to band antennas mounted outdoors, clear of nearby trees or buildings. Even then, you're starting with a barely double digit NM estimate which is very weak in the L_VHF band due to the added noise and interference at that frequency range.
I know of no popular DIY antenna designs that cover the L-VHF band but you can create your own design with the aid of software mentioned here:
http://forum.tvfool.com/showthread.php?t=1106