[Radio Wrangler]

The mixer is a "Single-balanced' type.

There are also unbalanced mixer types and double balanced types (and some exotic jobs!)

The balancing of this mixer nulls passage of signals from the RF port straight through to the audio amplifier. Any strong RF signal can overload the audio amp and cause self rectification in the semiconductor junctions, thus demodulating any AM they may have.

So the resistor does NOT help remove AM, it helps remove all signals trying to get straight through. It's only the AM ones that you'll hear.

Correct adjustment won't give you dramatic cancellation, but every bit helps.

David