I'm trying to mix a song with the aesthetic of that old AM radio sound. any ideas what fequencies I should cut to achive the desired sound?

oh, I would EQ the Master fader in the final mix right?

If you wanna be really intense about it, you should take whatever you want to sound like AM radio, and play it through two speakers, two identical speakers, like your monitors or stereo speakers or something... but flip the speaker leads on one of them, so it's out of phase... and then aim the two speakers directly into each other, from just a couple inches apart. The phase cancellations will take out the low end, and depending on how close the speakers are and where you place the mic, you should be able to get the mids and highs sounding good, too. Even if it doesn't sound like AM radio, it's gonna sound cool.

yea! that sounds like a fun experiment too!

I forgot to mention, what I said is something that would go well with roughly what BadComrade suggested, that being to cut out the high end as well. I think you might need to cut everything above 5K or maybe 3K even.

According to my instructor last week, AM radio cannot go below 80hz or above 6khz.