[R-390] 1.0 and 0.1 filter settings

[Barry]

Can someone give me the "Reader's Digest" version of how these two settings
work in an R390A?  I'm working on restoring the modules for my newest
project.  After replacing C553 (just to be safe), I plugged it in place of
the IF deck in my working R390A.

It seems all four filters are working; however, when I switch to 1.0 or 0.1,
the signal disappears almost completely, no matter how closely I tune to the
frequency.  I can see that the crystal and its parallel adjustable capacitor
are always in the circuit, but going to 1.0 switches out the extra cap and
switching to the 0.1 position adds some extra circuitry into the mix.

I don't quite understand how these other two settings do their job.  If
someone could elaborate, I'd appreciate it.

Thanks,

Barry - N4BUQ