[Boatanchors] difference bet. 75A3 and A4?

[Eugene Hertz]

Can anyone give me a brief comparison of the collins 75A3 and A4 receivers? I've been *toying* with the idea of getting a ham only receiver as opposed to my sp600.  I tried to find some info on the internet, best I found was that the A4 had better audio response.  Are the vastly different or moderately different? Frankly, I prefer the look of the A3 in the more traditional chassis/cabinet look but if the A4 is vastly superior I could be convinced.

I understand that the mechanical filters in both allow some kind of ssb reception (2.8k? 3.1k?) but I have also heard that a product detector is even better and would be desirable for either the 3 or 4.

Thanks!
Eugene