[Milsurplus] BC-221 with noisy tuning

[Ian Wilson]

Once I opened up the capacitor compartment the tuning mechanism
looked rather dry. I blasted the capacitor plates (with the capacitor
set to max C) with a can of no-residue switch cleaner, and applied
a tiny quantity of XYL's sewing machine oil to the two bearings and
the antibacklash gear. This cleared up the warble very nicely.

I notice that this unit has a very nicely made modification: a separate
ceramic trimmer has been added across the crystal frequency setting
trimmer. The new trimmer has been mounted behind the nomenclature
plate and a hole made in the box - but not the plate. The result is that
you can trim the crystal reference frequency without removing the unit
from the case, and the modification is invisible once you re-attach the
nomenclature plate.

73, ian K3IMW



On Mon, Jun 10, 2013 at 10:12 AM, J. Forster <jfor at quikus.com> wrote:

> Put a receicer w/ a BFO nearby and listen. Then gently tap things,
> possibly starting w/ the oscillator tube. When you finde thye thing that
> warbles you're done.
>
> -John
>
> ==============
>
>
>
>
> > I have a BC-221 with integral power supply. When I monitor the frequency
> > on
> > an external
> > set, tuning slowly has a distinct 'warble' to it. This feels like some
> > sort
> > of mechanical problem
> > (although I imagine it could also be due to something like metal whiskers
> > on the tuning
> > capacitor blades).
> >
> > Once I stop turning the tuning control the output frequency is rock
> solid.
> > I can move it up/down
> > smoothly with the 'Corrector' control.
> >
> > The tuning control doesn't have any grittiness to it when turned, but of
> > course there could be
> > backlash in the drive mechanism.
> >
> > Suggestions welcomed.
> >
> > 73, ian K3IMW
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