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Re: [TenTec] ? Century 22

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] ? Century 22
From: Garry Nichols <garrnich@gmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 22 Aug 2021 13:10:15 -0400
List-post: <mailto:tentec@contesting.com>
A speedy reply!  Thank you, Ralph!

I use stereo phones.  I agree that the built-in speaker is quite cheesy
sounding.  Am thinking I might remove it and mount it in a separate
enclosure that I will attempt to optimize for sound quality.  Maybe a tuned
duct mechanical filter as I have seen posted in a few places.

I did improve the sound of the radio a lot with a homebrew LC low pass pi
filter in the output.  I am also using an attenuator pad ahead of it as was
suggested in the manual for use with low Z phones.  The filter is low Z.

The radio still seems to have a resonance that is very sharply tuned even
when the AF filter is completely "out".  It is rather touchy to find it
while tuning.

TU ES 72,

Garry

On Sun, Aug 22, 2021 at 12:57 PM Ralph Matheny <mathenyr@marietta.edu>
wrote:

> The C-22 is a really neat radio.
>
> Before you mess with the audio filters
> try using an external speaker.  As I remember
> the one I had (and wish I still had it) sounded
> pretty "plastic" with the built-in speaker.
>
> I think I lowered the center freq by adding
> .001 caps across the ones in the design.  Think
> that was too low, you might broadband the
> filter by not changing all the cap values.
>
> Good luck.
>
> de K8RYU
>
>
> ________________________________
> From: TenTec <tentec-bounces+mathenyr=marietta.edu@contesting.com> on
> behalf of Garry Nichols <garrnich@gmail.com>
> Sent: Sunday, August 22, 2021 12:45 PM
> To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
> Subject: ? [TenTec] Century 22
>
> *** CAUTION: This email is not from Marietta College. Do not click on
> links or open attachments unless you recognize the sender and trust the
> content is safe. ***
>
>
> I've been approved at the Ten-Tec groups.io discussion but it looks like
> some folks are still at this discussion site.  No one replied to the post
> Gary made for me before my approval, so I will repost here to see if I get
> any replies.  TU,  Garry  WA1GWH
>
>
> I picked up a C-22 in July, S/N 666.  Does anyone know how many were
> produced? I am wondering where mine sits in the production run and what
> might have been changed along the way.
>
> I've heard that some of these rigs had capacitors in the AF filter that
> lowered it to 500 Hz center frequency and that C41-C48 (.0033) should be
> replaced with .0022.  Have not examined that on the board yet but wondering
> if by #666 this had been corrected.   And if those cap numbers and values
> are correct.
>
> The variable bandwidth AF filter is very effective but I do not like the
> way it sounds.  It is always set for minimum bandwidth and the adjustment
> pot just bleeds varying amounts of unfiltered AF into the output stream to
> the LM380 to widen the bandwidth.
>
> Because it is set for minimum bandwidth (200 Hz in TT specs) it has a
> pronounced "sea shell" effect on the audio.  This is apparent even when
> blending in large amounts of unfiltered AF.
>
> Is there any mod to widen the bandwidth?  Looks like I can drop off a stage
> or two of filtering to widen it as was done with the C-21 switch selected
> bandwidths.  I have pretty good mental selectivity.
>
> I would also like to lower the center frequency somewhat below the 750 Hz
> design.  Is there a mod for this?  (I've apparently answered my own
> question, above.  But with the filter dialed out the rig still seems to
> have a peak around 750 Hz to my ear.  Perhaps there is some filtering
> before and/or after the AF filter?)
>
> My radio has the built in Ten-Tec keyer but I get unsure code with my
> iambic paddles (which I simply push side to side, no squeeze keying).  I'm
> thinking the keyer might need a single paddle key to work correctly?  I may
> be confusing it with a dot or dash inserted reflexively before I let go
> completely of the other paddle.
>
> The drivers and the finals are not the same as are shown in the Ten-Tec
> manual circuit diagram.  The circuit shows an MRF476 for a driver and my
> radio has an MRF472.  I think there is something coded before the MRF472
> but it cannot be made out.  There is something after the MRF472 and a space
> but its initial coding cannot be made out.  I can see that it does end in
> "12".
>
> The finals are shown as MRF475 on the circuit diagram but my radio has
> 25073 then a space and an M with the rest obscured but the field ends in
> 824.
>
> I have heard that there were changes and substitutes for the drivers and
> finals along the way.  Can anyone give me any info on my situation,
> please?
>
> The rig's signal seems fine.  I have only taken it to 10W so far out of
> caution.
>
> And the last point:  The QSK sounds a bit "sparky/poppy" at times.  Is this
> the way these rigs are supposed to sound?  My SW-40+ and 4SQRP Cyclone 40
> also have these sounds to some extent.
>
> Thank you for any comments that might be made.
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