Thank you for the reply, Gary! I have not checked the component values on
my filter board. I need to do that.
I know that there is talk that TT goofed and set up the filter for 500 Hz
at some point in the run. Mine is number 666 so likely near the end of the
run. One would think they would have corrected it by then!
When I dial in my filter it seems to still peak at the same frequency as
when the filter is out, only it is narrow band. Matching the tonal
frequency of the calibrator when tuned for the loudest signal to my Ham
Morse app frequency (which I can adjust to specific values) comes out to
about 725 Hz and spec for the radio is 750 Hz. So it's in the ballpark!
73,
Garry
On Wed, Aug 25, 2021 at 7:10 PM Gary Tennyson <garyandjanice2@gmail.com>
wrote:
> It looks like IC3 has 4 op-amps that are used in the audio filter. This is
> page 17. These are four identical multi-feedback bandpass filters in
> series. Unless I made a math error, it looks like their center frequency
> is appx. 500 Hz.
>
>
> Gary Tennyson
>
> On Wed, Aug 25, 2021 at 8:21 AM Garry Nichols <garrnich@gmail.com> wrote:
>
> > In my last post I had asked members a few questions about the Century 22
> > circuit. And had intended to provide a link to the circuit diagram, but
> > did not!
> >
> > Here it is, and the RCVR/CONTROL board that I was asking about is on pdf
> > page 17 in case anyone might want to have a look:
> >
> >
> http://www.tentec.com/wp-content/uploads/2016/05/Century_22_Manual84ce.pdf
> >
> > Here is my post again, from several days ago:
> >
> > Hello All,
> >
> > I got out my Ham Morse app which allows changing the tone to a specific
> > frequency and tried various tones until I got a close match to the
> Century
> > 22 peak signal with the filter dialed all the way out. That is, no AF
> > active filter engaged.
> >
> > It turns out to be around 725 Hz, quite close to the spec of 750. To my
> > ears it does have a bit of width but that little band tunes fairly
> > sharply.
> >
> > I tried this with both the speaker and the stereo phones that I use.
> >
> > 725 is a bit high for me, so I am wondering if anyone knows of any
> > frequency shaping components in the audio chain other than the AF active
> > filter. I will puzzle over the circuit diagram a bit more to see if I
> can
> > pick out some likely candidates to experiment with. I'm thinking that
> > maybe something like 625-650 would be nice unless there is some reason
> not
> > to take the radio there.
> >
> > The manual does not mention an AGC for the rig. Does anyone know if
> there
> > is any AGC?
> >
> > I see a BJT right after the mixer filter along the balanced detector"s
> > output (on the RCVR/CONTROL board). Its base connects to the S-meter
> > circuitry. I also see a BJT connected just before the input to the AF
> > power amp.
> >
> > Both the S-meter circuit and the BJT next to the power amp have arrows
> with
> > a "T" indication. I am thinking that the "T" indicates the transmit
> > function. But, I see a "T" indication coming off that board on the
> chassis
> > wiring diagram for three different multi-contact connectors and each "T"
> > going to a different board! Does anyone know if those two BJTs are
> > involved in muting or AGC?
> >
> > TU,
> >
> > Garry WA1GWH
> > near Syracuse, NY
> > _______________________________________________
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> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
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