[TenTec] AF filter mod in Century 22

[Garry Nichols]

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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> >
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