[Hallicrafters] SX115 variations in serial numbers

[Joseph Trombino Jr]

Have been pondering purchasing an SX115 receiver and am wondering if there 
are any major qualitative differences in this series of receiver based on 
serial number, i.e., between a low serial number like 002 or 003 and the 
higher serial numbers up to the last one produced.

Also wonder how this receiver stacks up against a Collins 75A4?

Thanks for any information the collective wisdom can provide.

                                    73, Joe W2KJ