Yes, rod pulled out for maximim selectivity (highest "Q")............
the reciever's front end needs a pretty stable local oscillator to keep a
signal inside the new, 85kc IF bandpass.
Old Chief Lynn, W7LTQ
It isn't the Q but rather the mutual coupling between primary and
secondary windings. Hammarlund had a patent on this kind of transformer
which it used in the Super-Pro series of receivers. In the Super-Pro two
of the IF transformers have movable coils which are controlled via cams
operated by the selectivity knob on the front.
Richard Knoppow
Well, to be sure, the scheme (old as you and others remember) sure
does change the mutual coupling between the primary and
secondary windings, but mutual coupling as a factor by itself does not
affect
bandpass. The mutual coupling adjustment, in this instance, by moving one
coil
into or out of another's magnetic field does affect the "Q" or "quality"
factor of
the tuned circuit's inductor. This, of course affects the resonant bandpass
shape,
Changing the coil's mutual coupling mechanically (pulling the rod) also
affects the tuning of each coil slightly, and it was sometimes recommended
to
"repeak" the tuning of the '453's cans after changing the coupling. I found
that
I could not tell any difference by "ear", and in those days (late 1940's) I
had no sweep generator
or oscilloscope to "see" what was happening.
Old Chief Lynn, W7LTQ