I'm looking for plans for a simple AM antenna to connect to my stereo to
replace the little loop antenna that came with it. In the past I have used
long wires but they are not very directional.

I have found some fairly good plans online for what looks like wire wound
around a box but all of them seem to have potentiometer in the mix
somewhere. It would be very little problem to build an aimable 18 to even
48 inch frame.

I only have two AM stations I'd like to come in clearer (690 KHz and 1440
KHz). Would it be possible to make a 'box' with one 'tap' for 690 and one
for 1440 then just connect one or the other the radio? How long would be
wires need to be and how would I feed it into the connections on the radio
(coax)?