Allow me to chime in:
Yes, the keyer is not iambic, so if you are used to a dual-paddle keyer,
you will get messed up in short order, until you train you brain to use
either type of keying. I use mine with a Ten Tec single paddle or more
often with a straight key, for that "back to basics" feel, which is
appropriate for that type of radio. Any positive key line external
keyer will work, however.
My Century 22, third hand, is s/n 00364.
The audio filter is indeed, the classic op-amp analog filter, in all its
glory. The filter is actually in the circuit all the time. To increase
the bandwidth, the bandwidth pot mixes in unfiltered audio. Fully CW
is maximum bandwidth. Mine sound fine and it takes out the local
neighborhood plasma TV noise, which the noise blankers in my other Ten
Tec gear won't. You can peak the filter with the S meter.
The original drivers and finals were MRF476 and MRF475, respectively.
Because of reliability issues, Ten Tec replaced the drivers and finals
with 2SC1969. Be very careful about SWR. There is no SWR protection in
the rig; it depends on a fast-acting 5A circuit breaker or requires the
use of the Ten Tec 979 power supply which has a automatic over-current
shutdown. If you use this supply and are not sure where it's been,
check the current limit setting. Without protection, a couple of dits
sent into the wrong antenna will instantly destroy the finals. Don't ask
me how I know! Fortunately, I was able to find a pair of 2SC1969s at RF
Parts. If you need finals, try to get the original Mitsubishi brand.
There are a lot of Chi-com counterfeit 1969s that are sold for the CB
market. I downloaded a manual that had some notes typed in by G3VTT on
setting the driver and final biases.
Whether you use low -Z or high-Z headphones, the receiver will sound
much better if you use an attenuator (fixed or variable) and a matching
transformer, if needed. This will avoid both excessive noise and
blowing your eardrums out.
Sooner or later, you will have to replace the dial cord elastic.
I have collected some notes from various sources on maintenance and
mods, including the filter mods, which I will be happy to e-mail.
Now does anyone have a scan of the 979 power supply instructions or
schematic? It isn't on the Ten Tec manual download page.
73,
Bob WB2VUF
On 8/22/2021 1:58 PM, Garry Nichols wrote:
Thank you, Mike. The radio without filtering, but with my LP filter,
sounds quite nice. But I do need the added filtering for operating and am
attempting to make it sound better than it does. Perhaps components have
aged and it is not operating at spec. I'm slowly looking into all this.
Thought I'd ask other aficionados so as to not reinvent the wheel!
72,
Garry
On Sun, Aug 22, 2021 at 1:52 PM Mike Bryce <prosolar@sssnet.com> wrote:
The filter upgrade helps to kill off some of the high end hiss. I did
mine, but for the life of me can’t say I can tell a big difference. Is
there a change? Sure, but I don’t know if the time/labor/money was worth it.
The audio filter is analog and based on op amps. They do sound odd, and
it’s the nature of the beast. At the time this was sold, it had (still
does) an amazing amount of filtering. It’s all in the audio chain, remember
this is still a direct conversion receiver.
because the filtering is analog, bandwidth is set via the C/R combinations
within the filters. Dig out the necessary look up charts and plug in
different values to suit your needs.
Remember, this is an old radio. Don’t try and make it into something it
isn’t.
The optional keyer was a KR5 for all practical means. It’s not a great
keyer! It makes dots and dashes. There’s no dot/dash memory, and while the
dashes are self completing, you can’t insert a element until the one being
produced is finished. It certainly is NOT IMABIC. If you use it long
enough, you’ll send damn good code. If not, then you’re like me and the
code I send using one simply sucks.
The PA in this rig has always been know for issues. One is they changed
designed throughout production. It doesn’t matter what the schematic shows,
replacement if necessary, use the ones in the radio. The last time I did a
PA transistor replacement, the parts were hard to come by and expensive. RF
parts is your friend in this case.
The bias needs to be checked after you replace the drivers or PA
transistors. The manual tells you how to do that.
If you don’t like the QSK, most likely a capacitor can be changed in the
T/R circuit to slow/ease it down. I don’t have information about that off
hand.
Personally, I’d enjoy the radio as it, warts and all, and know that’s how
it worked way back then.
Mike, WB8VGE
SunLight Energy Systems
The Heathkit Shop
http://www.theheathkitshop.com/
J e e p
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