[Boatanchors] Crystal Effects

[Stanley Adams]

Hello Ron

The crystal is in a four legged bridge circuit, when you adjust the phasing
control it introduces capacitive  and inductive elements and thus allows you
to effect the passband of the crystal, so yes the center of freq will shift
a little when the phasing control is operated.

However, and this is important, if the receiver is aligned, it must be
aligned to the center freq of the crystal filter, which is almost never 455
kc.  It might be closer to 456 or so.  What you do is put just tune in a
weak to moderate powered station, you do not want a real strong station for
this.  You take a voltmeter set to AC and put it on the output leads along
with your speaker, turn the vol up enough to get a meter reading and or set
your scale so that a meter reading is obtained. Now you can carefully rock
the tuning knob from side to side while on the station.  Make sure the
filter phasing is centered or off.  While rocking the station slightly
notice where the AC meter peaks, that will be the center passband of the
crystal..  If you use a signal generator make sure it is warm and has been
on for a long long time and is very stable, you can tune it to 455 and
slowly rock the oscillator from side to side and you will find the center of
the xtal filter.  That is THE center of the passband of the xtal and you
align the coils up with that.

But it is common for the freq to shift a little yes when you tune it.

Stan Adams
Memphis
W4SBA