It was touted for a while as having Collins mechanical filters. I'm not sure of how this got put around, but I came across the statement from an owner of a surplus one in a certain treasure cave called M&B Radio in an archway under Leeds city station.
I've got a 1792 in the attic and the manual for it, I'll take a look sometime.
The Racal fan club in the 1980s were ecstatic over a newer receiver appearing on the surplus market and were convinced that as a newer model it had to be even better than the 1772
David