While not all inclusive to my experience, it was a noticeable difference from the TR44 which uses the T4X that the SSB use either had to have the key closed or the key jack empty.? On the B and C line, this is not the case.? As I just finished restoring the R4A and T4X, I will have to remember this.? As to an all encompassing?list of these changes, I know of none; but it would be handy for those folks who switch around from radio to radio.
Nice piece of history.? I guess that Drake did indeed pay attention to user feedback on future designs.