[R-390] unstable BFO note on R-390A
Bob Young
youngbob53 at msn.com
Sat Dec 16 17:18:11 EST 2006
Dan,
Thanks, but the problem is that there is a flat part on the shaft where the
set screw goes which only allows a little leeway either way for the knob.
The gear I'm talking about is the split gear that is right behind the main
tuning knob if I remember right. It is supposed to eliminate backlash I'm
pretty sure. When I wiggle the main tuning knob with the BFO centered and on
I can knock it off zero beat by wiggling the knob, sometimes it goes back
other times no. This is without turning the knob at all, it will jump all
over the place. I'm wondering if this could be in the VFO or is something in
the gearing mechanism or maybe because the springs are not equal the split
gear is not functioning properly? not sure, oh also when tuning in a station
with the .1 khz position it is also very hard to keep it peeked and tuned it
jumps all over the place also along with the BFO if that helps.
Bob Young
Millbury, Ma
>From: "Dan Merz" <mdmerz at verizon.net>
>To: "'Bob Young'" <youngbob53 at msn.com>, <r-390 at mailman.qth.net>
>Subject: RE: [R-390] unstable BFO note on R-390A
>Date: Sat, 16 Dec 2006 05:48:30 -0800
>
>Bob, yes it's an easy fix to "align" the bfo. Loosen the set screw on the
>knob, remove the knob, set the bfo at the correct frequency of the center
>of the i.f. by "zero beating" the noise (or on a signal that you know is
>coming down the center of your i.f., for example thru the xtal position)
>and
>then without moving the setting, reinstall the knob with the indicator at
>the top zero position. I'm not sure what gear you are talking about as
>the
>bfo shafts on my radios go straight into the coupling to the bfo bellows
>and
>turn the pto directly.
Bob, the problem you are describing could also be the VFO. I recommend you
try the following.
1. Set the BFO to center frequency by doing the following. With the BFO off,
and the BANDWIDTH at 1KC or .1KC tune in a strong local BCB station peaking
the signal on the CARRIER meter. This peaks the signal in the bandpass of
your crystal filter. Now, without moving the KC knob increase the BANDWIDTH
to 4 or 8KC, turn ON the BFO and zero beat the station using the BFO tuning.
When zero beat is found loosen the knob and center the BFO knob at this
point. Now when you want to zero beat a BCB station with the BFO leave the
BFO knob set at zero and use the KC knob to zero beat the signal. Doing this
will insure that the incoming signals are in the center of all those
mechanical filters.
2. Now for the warbling of the beat note. There is a small strap that is
mounted at the base of the VFO shaft and rides on this shaft. The end has a
vee notch where it rides on the shaft. Carefully clean this area so as to
restore it's grounding ability. While you are there apply just a drop of oil
where the VFO shaft enters the front of the housing.
Hopefully these two hints will improve your situation.
73
Don WC4G
Don,
I'm going to check this procedure later tonight and also check Chuck's
website and also the Pearls,
thanks
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