how do i know if the R71A that i am consiering purchasing has jus the
notch filter or the PBT/notch? I can tell you this the unit says only
notch above the pot. on the faceplate, but i read somewhere that the
unit could still have PBT even though it only says notch. also the
serial number is 03xxxxx.
any r71 experts that could help me out. if it doesn't have the notch
could it be modified? also what is the difference between the r71a, d
and e?

thanks in advance, john