[TenTec] Century 22 circuit diagrams

[Gary Tennyson]

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 at 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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