The design used plug-in coils for the osc and rf stages, and
they were double conversion designs, with a first IF of
1600 kc and a second IF of either 100 kc or 85 kc (when
using surplus ARC-5 IFTs.) The 1800 mc xtal you bought
your dad was used for the second coversion osc. to convert
the 1600 kc IF down to 100 kc. Many hams deviated from
the exact original IF frequencies (i.e. strong local BC
station on 1600 kc) which might explain why the xtal
was chosen for 1800 kc instead of 1500 or 1700.


We have a local mid power station at 1600KHz, WWRL, at my parents' house,
so my father might have wanted to avoid problems with it.

His radio had a bandswitch instead of plug in coils, and he'd receive
various broadcast SW stations. He wasn't a ham at the time just yet.