Thank you, Jim. Well, I'm in Tacoma, if that's considered close to the Canadian border (+/- 3 hr drive on a good day). Shipping it to Arkansas? Return shipping would be a few times the worth of the thing, and who knows what UPS or one of their cousins would do to it, even if double boxed (as I know from experience).
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In the meantime, my SX-28 stopped working last fall and I've been avoiding it ever since. I need to take a deep breath and dive into it, but not just yet.
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Tom
On 03/16/2025 2:08 PM PDT Jim Whartenby via groups.io <old_radio@...> wrote:
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Tom
That is a shame.? I was just wondering if you had made any progress.? Perhaps a list member up in the north-west area of the country would be interested in having a go at it?? How far are you from the Canadian border?
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I'm in Arkansas over 2000 miles away from you so that would be a lot of shipping expense for me to take a look at it.? That said, the furthest I have done a repair was for a gentleman in Fukushima, Japan.
Regards,
Jim
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Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
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I certainly appreciate all the advice, hints and overall help I received in my attempt to resurrect this fine old survivor but, for me at least, I think the journey is over. Properly servicing the mixer section means that the LO coil assembly will have to be sufficiently lifted or even removed from the chassis. I found that doing so is beyond my ability. This assembly is connected to the main tuning capacitor by a connection that I am unable to de-solder in such a tight spot. It would take a heftier soldering iron than either one of the two I have, and even if I could, I doubt my ability to reconnect it. I'm a hobbyist, not a technician with the experience to deal with such a challenge.
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It's a pity--I think this receiver would be very serviceable if repaired, and be capable of performing as well as most vintage, single conversion receivers lacking a crystal filter. So, back on the shelf it goes. I'll hold on to it for a while--after all, not too many people are going to want to tackle a receiver with challenges like this one.
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Thanks again,
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Tom
On 03/09/2025 6:11 PM PDT don Root <drootofallevil@...> wrote:
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Jim & Tom?
The Hexode signal grid has a max? or min? voltage of -3? presumably to the cathode [depends who you read] , but my conclusion from a Sylvania ??blurb? is that it can go as positive as -3 volts, and as negative as -30 where there is little transconductance, and so is often connected to the AVC, but apparently not in the S-20R. but that does not help the situation.
As Jim says, on band 1 ?there is no ground, and I say there is no control of THAT grid voltage by ground, AVC or other, so it floats. On the other bands the bottoms of ?3,2,1 can be grounded [all depending] providing a DC ground ?but it goes thru the coil{s} so is strange to me. But band 1 is a real mystery to me too. ?
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Tom, I suggested a test for the bandswitch area? was it not practicle? ?
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That is interesting.? The tube manual indicates that -3 volts should be there.? Have you replaced C5 and C8?? Minor leakage in either could cancel the expected negative bias on G3 of the 6K8.? From the QST article, I expect that there are unintended interactions when the expected voltages are out of spec.
In looking at the schematic for the umpteenth time, I see how the upper band tank coils are returned to ground through switch 7D rotor that shorts the bottom of the band coils to ground.? Not sure how L13 is grounded when the band switch is in the BCB setting.? If you measure the DC resistance from the grid cap to ground you should measure R12 (33 ohms +/- 20%) plus the coil resistance for each band switch setting.? Is this the case???
Measuring from the switch side of R12, you should measure just the tank coil resistance to ground.? That resistance should increase as the band switch connects to the next lower tank coil.? If you don't see the coil resistance then perhaps the oscillator stator sections of either C1 or C2 is grounded?
Likewise, the switch side of C37 should measure the LO coil resistance to ground for each band switch setting.? Like the above, each lower band coil resistance will be higher.? Is this the case?
Remote troubleshooting is a s-l-o-w process,
Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Sunday, March 9, 2025 at 11:47:14 AM CDT, Allthumbs via groups.io <btse1@...> wrote:
Thank you, Jim. The 6K8 control grid (grid cap) measures 0.00 vdc, pretty much as expected.
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don??? va3drl
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Allthumbs