[R-390] unstable BFO note on R-390A

[Dan Merz]

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.  Perhaps you were referring to some interaction of
zero beat when you were using the main tuning knob,  which has gears.  Or
maybe you radio is different than mine and has a geared bfo.  There may be a
problem with either the coupler on the shaft directly behind the panel or
with the bellows coupler within the i.f. chassis.  Can you peek into the
radio from the top and see if the coupler behind the panel is secure.  I've
had one of mine fail by cracking and it couldn't be tightened enough to be
secure. Or perhaps the bfo tube is bad. 

If you are using the bfo to zero beat broadcast stations at known
frequencies,  there is no guarantee that the tuning indicator will indicate
the correct frequency unless you calibrate the main tuning to indicate
correctly on the band of interest and near the frequency of interest,  which
is a process separate from the bfo alignment.   I would guess the usual 390a
will not indicate frequency to within 200 cps (1 division on the wheel)
without calibration on each band even if you align the bfo perfectly,  at
least mine won't.  I'm happy to be within 1000  cps in going from one tuning
range to another without re-calibrating the tuning indicator on a nearby
signal of known frequency or using the internal calibration oscillator. I
recall that my set is only within about 500 cps in going from one end of the
range to the other if I calibrate it at the middle of the band.  And that
was after opening and adjusting the range of the main tuning pto. Old is
good but not necessarily as good as it was.    Dan. 

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Bob Young
Sent: Saturday, December 16, 2006 2:55 AM
To: r-390 at mailman.qth.net
Subject: [R-390] unstable BFO note on R-390A

I use the BFO frequently to zero beat the carriers on BCB. It is off by
maybe 200 CPS for one thing after moving the BFO knob as much as it could go
to one side, is this an easy fix to align the BFO? Also although I feel no
backlash it is jumpy when tuning with it on. If I move the tuning knob up
and down the BFO will jump to differing frequencies and sometimes stay off
center. One of the springs on the split gear is shorter than the other,
could this cause this problem, or is this more indicative of worn gears
maybe? Any other ideas? thanks, it is worse when warm.

Bob Young
Millbury, Ma


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