[R-390] IF sweep alignment

[Bill Hawkins]

Haven't seen any mention in this thread of the mechanical filters
in the A version.

You may recall that there was a hybrid combination of the A and
a non-A IF deck (R-725) because the mechanical filters prevented
fine direction-finding operation. Ringing mechanical filters,
IIRC.

There was also at least one thread in the good old days of this
list that strongly advised against trying sweep alignment of the
IF strip, because the ringing filters distorted the wave form.

Perhaps you could use a wide band 455 KC receiver before the
filters to see the response curve of the IF transformers before
the filters. You can't align the filters anyway. What you do is
find the center of the 100 Hz filter (does an A have that crystal
filter?) and use that as the base frequency of the sweep generator.

Hope this stirs someone's memory.

Bill Hawkins