[amsat-bb] Transystem 3731 vs. 3733

Can someone tell me the major difference between the two downconverters? Ten years ago or so, I used a 3733 un-modded at the fed point of an 8ft dish to copy ao-40 tlm. Today I read a lot of references to the 3731, but not much about the 3733. Just wondering if one is preferable to the other.

Rich, N8UX