[TenTec] AF filter mod in Century 22

[Josh Gibbs]

Hi Gary,

I have not modified mine. I think a previous owner might have changed some
parts, but not sure. I should probably take a look and see.

-Josh WU7H


On Tue, Mar 28, 2023 at 3:45 PM Garry Nichols <garrnich at gmail.com> wrote:

> Thank you, Josh!  A speedy reply!
>
> I have two mods from others going from 500 Hz to 750 Hz CF and they only
> mention replacing the 8 caps.  Did you modify the bandwidth from factory
> spec also and that was why the resistors were also replaced?
>
> I guess it is possible that the early factory 500 Hz value produced not
> only a low CF but a poorly performing filter.  Was your rig set to 500 Hz
> when you got it?  What was that like?
>
> I'm not sure what bandwidth I would have without replacing the resistors.
> I guess I could use that calculator to figure it out after reading the
> resistor values in the rig or circuit diagram.
>
> I'm not sure what Q value to enter if I decide to change resistors.  How
> did you decide or did you just follow that mod's values for C and R and
> wind up with the same performance as changpuak, (I guess the author is?).
>
>
> I'm not sure what bandwidth to set each stage to.  I don't want it too
> tight because it gives a more pronounced "seashell" sound.
>
> Opinions welcomed from anyone.
>
> TU,
>
> Garry
>
> On Tue, Mar 28, 2023 at 5:36 PM Josh Gibbs <gibbsjj at gmail.com> wrote:
>
> > Hi Garry,
> >
> > I have C22 number 68!
> >
> > Have a look at this:
> >
> >
> https://drive.google.com/file/d/1ZMjJoC9GQkRfRBUEicwEodOghOthEyNd/view?usp=share_link
> >
> > Look at the section "Modification center frequency of audio filter" near
> > the end.
> >
> > Hope to have a C22-to-C22 QSO with you some day.
> >
> > -Josh WU7H
> >
> >
> > On Tue, Mar 28, 2023 at 2:22 PM Garry Nichols <garrnich at gmail.com>
> wrote:
> >
> > > I have an apparently fairly late Century 22 (serial #666) and the AF
> > filter
> > > seems to peak around 750 Hz.  This does not set well with my old ears
> > and I
> > > know that some of the early rigs came from the factory with .0033uF
> caps
> > in
> > > the filter that set the center frequency to around 500 Hz.  My rig has
> > the
> > > .0022uF caps which are the specified mod for 750 Hz.
> > >
> > > I was thinking of changing the .0022uF to .0033uF and was wondering if
> > > anyone knew if this created any problems in addition to lowering the
> > > frequency.  No point in doing this if I end up undoing it!
> > >
> > > I guess I could also set the value somewhere between but it would seem
> > that
> > > I might tack in some .001uF as a trial for about 500 Hz.
> > >
> > > TU ES 73,
> > >
> > > Garry WA1GWH
> > > near Syracuse, NY
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