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Re: [TenTec] Troubleshooting Century 21 Power Issue

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Troubleshooting Century 21 Power Issue
From: Josh Gibbs <gibbsjj@gmail.com>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Mon, 7 Oct 2019 08:10:20 -0700
List-post: <mailto:tentec@contesting.com>
Yes, this is a good point Perry - sorry I forgot to mention that. T-T did
sell an external breaker for this purpose, but they are hard to find these
days. When I was running my C21 on external 12V I cobbled together an
over-current protection using an Arduino, a current sensor, and a relay.
Worked really well - parts to do it are cheap and easily available on
Amazon (less than $20).

I found my C21 was a lot quieter on external power - on the internal supply
there was a hum. I replaced all the electrolytics including the big supply
filter cap, and it had no effect on the hum. Consensus was the hum was due
to the headphones I was using - a swamping resistor or higher ohm phones
made the hum almost imperceptible. The hum wasn't noticeable on the
internal speaker. T-T added some shielding around the transformer to later
units that mine does not have - I suspect adding that shield would help,
but I was satisfied with the rig and didn't feel like taking it all apart
again =)

As for the sensitivity mod - I have not tried it. There is a guy on QRZ who
contacted me about it recently and he was planning to try it. I've talked
to Dick Frey K4XU about it (he designed the rig and currently lives south
of me in Oregon) and he said it's a good mod. If you look at the file
'Improve Sensitivity Page 2' on my Google link, you will see a schematic
that Dick sketched out. If you try it I'd love to hear your results.


-Josh WU7H

On Sun, Oct 6, 2019 at 8:14 PM Perry Ballinger <w8au@sssnet.com> wrote:

> Josh's idea of feeding 12V into the rear 12 Accessory socket works well
> but there is no overcurrent protection or meter reading.
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