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 Post subject: Allied / Radio Shack SX-190
PostPosted: Nov Sun 22, 2020 9:28 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1560
Location: Wayside, NJ Monmouth
I picked one of these up for a good price along with the matching speaker. After replacing some bad caps. I went ahead and replaced all the electrolytes. The radio really came alive after that repair. So I when ahead and did some mod's I found on line. Have to say for a 50 year old solid state radio she hears well. Two of the dial lamps were burned out. So I replaced them al with white LED's. Going to make room on the operating bench to shoe horn her in and hook up to the antenna patch panel.


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Last edited by N2LXM on Nov Mon 23, 2020 2:22 am, edited 1 time in total.
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 Post subject: Re: Allied / Radio Shack AX-190
PostPosted: Nov Mon 23, 2020 1:26 am 
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Joined: May Sun 16, 2010 3:22 am
Posts: 290
Location: Scotia, NY 12302
You say AX -190 but your photo is of a SX -190. The AX is the ham band version and the SX
is the short wave version. I also have a SX -190 but wish it was the AX. They are decent receivers
and I think they originally sold for $250 or so.

Al

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 Post subject: Re: Allied / Radio Shack SX-190
PostPosted: Nov Mon 23, 2020 2:24 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Wayside, NJ Monmouth
Thanks for the catch Al. I edited the post. Big fingers, small keyboard.


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 Post subject: Re: Allied / Radio Shack SX-190
PostPosted: Nov Mon 23, 2020 3:57 am 
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Joined: Jun Sun 19, 2011 2:31 pm
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GRE did a nice job with these receivers. You will find that the Q multiplier is very useful for CW operation with these sets.

I think that these were the best Allied/Radio Shack branded shortwave receivers. Although provisions were included for a matching transmitter that never materialized.

Rodger WQ9E


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 Post subject: Re: Allied / Radio Shack SX-190
PostPosted: Nov Mon 23, 2020 5:01 am 
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Joined: Apr Thu 12, 2007 3:24 am
Posts: 2509
Location: Milwaukee WI 53219
I suppose I can search the web too, but I'm wondering what other mods you performed. My SX-190 and speaker have been my bedside radio for at least 3 years now. In the warmer months it probably runs 8-12 a day. A little less in the cooler months where I do more listening on my tube type receivers. The only issue that cropped up is the USB oscillator won't fire up unless room temp is above 79 degrees. I'm sure it just needs a tweak of the oscillator cap or something else simple but I didn't feel like opening it up just for that yet. Among the many good things about the radio is the spot on dial calibration. I can tell within a 1-2 khz accuracy which is great for an analog dial. I kinda wish it had a better AVC. There is too much difference at the speaker between weak and strong stations.

edit: I forgot that the manual I downloaded a couple of years ago has a section on mods. But I suppose your list would still be good in case it has some not listed in mine.


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 Post subject: Re: Allied / Radio Shack SX-190
PostPosted: Nov Tue 24, 2020 8:03 pm 
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Joined: Apr Thu 12, 2007 3:24 am
Posts: 2509
Location: Milwaukee WI 53219
After reading thru the mods articles I decided to do a little experimenting.

I tried the 2 audio mods. Without a direct A/B comparison I can't tell the difference. No harm done so I left them in.

I was happy with the SSB reception as-is so I didn't do the BFO or AGC time constant mods.

While it looks cool, I didn't replace any bulbs with LEDs.

I did a more precise adjustment of the Q multiplier pots so its actually usable now.

Using my SDR as a spectrum analyzer I gave a very precise alignment of the VFO and LO stages. I zoomed in on the display for maximum accuracy. Before this alignment I was pleased in that tracking from one end of the dial to the other was off by only a little over the dial pointer width, about 2-3khz. Now it is dead on across the dial on all bands. I prefer this method of viewing instead of a frequency counter. Not quite as convenient but quicker and accurate down to the hz. But since most of my repairs are done in the basement away from my computer I'll still use a freq counter most of the time.

I tweaked the coil for LSB/USB oscillator. The USB crystal fires up a little more reliably but not every time. It is the crystal itself that is temperature dependent. I touched my soldering iron on the metal body for a few seconds and it kicked right in.

I have the radio back together and realized I forgot to try the cap across the meter to to hold the peaks for easier readings on SSB. Its easy enough to try later. I just have to remove the top cover and not the whole case.

While nothing I did was an amazing night and day difference, it was enough to feel it was worth the effort. I'll add that it was great forsight for Allied to have the VFO and LO outputs on rca jacks on the rear of the chassis. It made connections for alignment much easier than finding and clipping onto circuit board testpoints or components.


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