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Hi Scott.? That’s good info. So the problem seems to be in the FM limiter /discriminator area ??I will do some head scratching, but others might have the answer first.

We had a day or two of nice weather, and I was out cleaning up flower beds so now I cant move.

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don??? va3drl

Hi Scott.? That’s good info. So the problem seems to be in the FM limiter /discriminator area ??I will do some head scratching, but others might have the answer first.

We had a day or two of nice weather, and I was out cleaning up flower beds so now I cant move.

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Scott, I’m not too smart and also can’t read between the lines and words.?

What is oscillating?, and at what frequency? I guess you see it on a scope unless it is from the BFO and out the speaker.??

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You mentioned nothing about the history and if you have ever had it receiving or not on any band. ?

Will it work on AM/CW on all bands ? ?and it is just the FM detector?

On FM what happens with the signal generator off and an antenna ..nothing?, stations? Oscillations most of the time?

Is your RG gain pot in good shape, or is it noisy, erratic? ???

I have a sx-62 of some version in sick bay so I am extra curious but it will take a while to understand things.

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I did both alignments, and all seemed well until I switched in FM, and the gain was too high, and it wouldn't receive until I turned the RF control to 2-3, and only "works" in a small range, either too high, and oscillates and blanks, or too low a gain to hear anything.

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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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On Sunday, March 16, 2025 at 01:55:57 PM CDT, Allthumbs via groups.io <btse1@...> wrote:

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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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From: [email protected] [mailto:[email protected]] On Behalf Of Jim Whartenby via groups.io
Sent: Sunday, March 9, 2025 2:46 PM
To: [email protected]
Subject: Re: [HallicraftersRadios] S-20R mixer cct. #photo-notice

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Tom

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.

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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???

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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?

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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,

Jim

Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy

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On Sunday, March 9, 2025 at 11:47:14 AM CDT, Allthumbs via groups.io <btse1@...> wrote:

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Thank you, Jim. The 6K8 control grid (grid cap) measures 0.00 vdc, pretty much as expected.

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Tom ?

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don??? va3drl

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On 03/16/2025 1:54 PM PDT don Root <drootofallevil@...> wrote:

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Tom,? well we all get worn down and discouraged when things beat us. Also, after concentrating on something, it is hard to see the forest ?for the trees.? So perhaps it is time for a break.? Most of us just dab in this, and learn bits and pieces from here and there. Maybe we [ me anyhow] speak over your head, since we as individuals don’t know “just what you know”. That is always a problem. It is best to speak up; this is not a competition, it is a mutual assistance group of non-professionals down to first time dabblers. ?While you have your nose in the Rosin smoke, I’m looking into info on the 6K8? and other converters, and so learning a little bit.

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For some time in the future, as to your problem , that cap must be C7 a 2200??F [or these days maybe 2200pF] connected to the cathode? and not C37 connected to the bandswitch.? You had a good voltage on the cathode, so it [and C8] don’t seem to be shorted and my guess is they are ok but cant be sure.

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I wonder if you understood the simple resistance tests on the coil area? that I sent before. ???

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don??? va3drl

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