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Old 14th Jul 2020, 4:47 pm   #41
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Default Re: Hallicrafters Sky Champion S20

No.
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Old 14th Jul 2020, 4:55 pm   #42
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Default Re: Hallicrafters Sky Champion S20

I meant to post this earlier today, this one also appears to show the BFO injected at the 6L7, also note the style of the last IF transformer compared to other photo's on the net and the layout in the manual. I wonder if that BFO injection point was a manufacture's mod/recommended mod or an amateur radio magazine article mod.

https://www.radiomuseum.co.uk/Sky%20Champion.html

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Old 14th Jul 2020, 8:26 pm   #43
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Default Re: Hallicrafters Sky Champion S20

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That cut wire and the one it was wrapped around it might be the BFO injection capacitor (C31 a twisted wire capacitor) a capacitor in that circuit position was often made up of two insulated wires wrapped together AKA a gimmick capacitor, perhaps you could confirm either way?
That is correct Lawrence. I experimented with wires of different length/ number of wraps when I was trying to get the BFO working on mine.
Attached is a photo of the underside of my chassis. Top right of the photo is the screened cable coming from the small variable capacitor which is the BFO control. It travels down to the bottom of the photo and disappears , but reappears over to the bottom left where it passes through a hole in the chassis (where I marked the 6K7 valve) and goes up into the raised box that holds the valve and transformer for the BFO.
The gimmick capacitor also went into the same box.
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Old 14th Jul 2020, 8:44 pm   #44
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Default Re: Hallicrafters Sky Champion S20

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Normal method is to inject a modulated signal at the IF. Connect an output meter in place of the speaker, or a 'scope across the speaker, and adjust the IF Transformers for maximum audio output.
That’s the way I did it following the Riders instructions. I replied to a pm late last night giving step by step instructions how I did it.
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Old 14th Jul 2020, 9:17 pm   #45
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Default Re: Another Hallicrafters Sky Champion S20.

I assume that the PM was to the OP?

If so let's hope the procedure works for him. Given that the receiver works to some extent, I can see no reason why it shouldn't.
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Old 14th Jul 2020, 9:52 pm   #46
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Default Re: Another Hallicrafters Sky Champion S20.

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I assume that the PM was to the OP?
M

Yes it was.
The IF was easy. The RF alignment much more involved.
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Old 14th Jul 2020, 11:40 pm   #47
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Default Re: Another Hallicrafters Sky Champion S20.

Between working on my normal stuff at my home office and working on the S20 I have had a flurry of confusing info about the set. So working on radio gear in a partial attention mode has its drawbacks in how the info comes out lol.

I am at a nice stopping point for just a bit: not much farther than I want to be unfortunately.

The OP did give me valuable info on the Riders procedure for alignment. The only other radio I ever aligned was my SX-43 I restored. While this set is simpler, paradoxically this set has been tougher.

To clarify where the set is:

- The set will receive a strong local station nicely at 1440Khz with a 10 foot wire antenna.
- I can detect a tone from a RF (modulated) signal from my Heathkit IG-102 anywhere on the AM band (strongest toward the 1400 end of the AM band, weakest less than 600).
- I have not been able to inject a RF signal into the 6L7 that produces a tone through the speakers (I did get the set to produce a tone when I followed Station X's advice on going to the volume knob).
- I am able to get a tone from a 1.4 Mhz frequency set on my signal generator (not 10 Mhz as I stated before - read the wrong scale...) around the same spot the one station that comes in is at (likely a harmonic artifact of some type?).
- I seem to be able to align it by ear for the one station and it comes in very well (listening to it now). In 1-1/2 hour there has been no drift. No other channels will come in as strong.
- I replaced the last two caps and resistor today: most components are either at nominal or close enough within normal 10-15% variation allowance.
- The tubes were re checked and I tube rolled through it my best tubes I have for the set - one at a time - to find the set the radio liked the best.
- The lead dress was not changed. I snipped a component and replaced it right away.
- The SW bands appear to not pull in any stations. When I connect my signal generator to the antenna I can get a tone close to where it should be on the dial, but after about 2 or 3 MC I cannot get anything (perhaps that means the oscillator drops off before it gets to that high).
- The 4th band is quiet, dead, and not accessible by my signal generator.
- I do have a snazzy RMA dummyload antenna module that BNC connects to my signal gen and signal/ground clips. I have also used the 0.1uF and 400Ohm specs called out in the John Rider documentation (used both to see which worked better).

I am taking a few days away from it to work on other projects - so for now the score is RADIO:2, me:1.

In the meantime any additional advice on debugging the set is most welcomed. Bear in mind I am a tube amp guy and much of what I know about radio was undergraduate studies that largely were not used in my profession. I would think the symptoms of what I have going on are not unique - I did go back and check the normal block & tackle stuff to be sure the set is capable of working properly.

Any specific things to try in detail I'll be glad to try - please if you suggest something to try give me some detail on it as I might not be familiar with the superhet circuit (or what I am doing and checking for)

So for now, it sits on the shelf taunting me with the one channel that comes in (in the pic enclosed).
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Old 15th Jul 2020, 12:12 am   #48
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Default Re: Another Hallicrafters Sky Champion S20.

1440kHz and 1.44MHz are the same thing. So I'm not surprised the 1.4MHz modulated signal gets through.

I'm guessing that by AM band you mean the AM broadcast band, which we call Medium Wave in the UK?

The IF stages must be working or you wouldn't be able to receive anything. Are you quite sure your SG is producing a modulated signal at 455kHz. Are you using the correct scale?
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Old 15th Jul 2020, 1:56 am   #49
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Default Re: Another Hallicrafters Sky Champion S20.

DOH - friggin hilarious i didn't catch that lol. The scales are all superimposed on the SG - and its an analog dial - except for my scope all of my other test gear is digital.

I will check on that specifically: if the whole time I could not get a 455khz signal is because its really something else I will buy a digital SG system as punishment
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Old 15th Jul 2020, 1:18 pm   #50
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Default Re: Another Hallicrafters Sky Champion S20.

I did check and cross check with another radio: there is no doubt that the signal generator is at 455khz. I am able to move up the frequency to above 550 and hear the tone by the S20 around where one expects on the dial.

I remove the 6L7 cap, clip the SG hot through a 0.1uf, and ground to the chassis as prescribed in the Riders documentation and I cannot hear anything through the speaker. I flip back modulated and un-modulated. I even fiddled with the coils T1/T2 in various combinations testing infinitesimally small changes for over an hour. No sound and I do not know why. Every indication is it SHOULD work. The radio can detect frequencies from a SG somewhat near where it should on the medium wave band (U.S. normal AM band). And I can pull in two (only two) channels on medium wave band when I manually tune the coils by ear and adjust the alignment pots (to further bring it them in clearer).

I have spent much time on this radio - in the pic you see what I have in queue in my shop. I get the cast-off basket case sets free (such as my SX-43 and S20) but I have a never-ending supply of museum-grade radios to go through to test, assess, and do minor repairs and been sucked into the vortex of this S20.

None of the hundreds (and literally several hundreds) of radios I am working on for a local estate broker will need the level of work I have done to my own radios, but I will peel time away and try anything else if anyone might have an idea for me to try.

I have every volume of the John Rider series in original (and library-mint) condition as a guide but being a metrology/instrumentation engineer and industrial automotive engineer by profession some of the specifics of radios I have not worked with directly. Any assistance will help the cause

I do have a calibrated and rather nice Hickok signal generator that is lightyears better than my simple IG102 I plan to hijack for use in the shop - as soon as I figure it out I'll even try it on my S20 (though the IG102 was able to fully align my SX-43).
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Old 15th Jul 2020, 1:27 pm   #51
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Default Re: Another Hallicrafters Sky Champion S20.

Try leaving the top cap connector on the 6L7 in place and clipping the output of the signal generator to it.

Lawrence.
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Old 15th Jul 2020, 1:43 pm   #52
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Default Re: Another Hallicrafters Sky Champion S20.

Do you have a frequency counter which you could use to check the frequency produced by the S20's Local Oscillator?

Alternatively you should be able to receive the Local Oscillator on a second set. For example if the S20 is tuned to 500kHz you should be able to hear its Local Oscillator as a hiss at or close to 500+455kHz or 955kHz as you tune a second receiver around 955kHz.
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Old 15th Jul 2020, 2:01 pm   #53
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Default Re: Another Hallicrafters Sky Champion S20.

I happen to be rather radio-rich in my shop and will try that right away. If I understand you correctly: for this sympathetic detection by another set the two must be very close together.

Is it possible to adjust T1/T2 using this method to move the 500+455 summation to be equal to 955?

The possibility the set may be so out of alignment that it defies conventional alignment means has crossed my mind. Being a novice superhet restorer these days I cannot discern if this is the case. Anything I have messed with thus far has "been in the ballpark" as the American term goes.

I'll report back on the status of this in just a bit - a most gracious thank you for the suggestion

Quote:
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Do you have a frequency counter which you could use to check the frequency produced by the S20's Local Oscillator?

Alternatively you should be able to receive the Local Oscillator on a second set. For example if the S20 is tuned to 500kHz you should be able to hear its Local Oscillator as a hiss at or close to 500+455kHz or 955kHz as you tune a second receiver around 955kHz.
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Old 15th Jul 2020, 2:03 pm   #54
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Default Re: Another Hallicrafters Sky Champion S20.

Great suggestion: I did try this and even just clipping the alligator clip on the insulation and even on the antenna. I messed with the power level of both the set and the signal generator in the event the set was getting overloaded and even tries clipping directly to the cap and antenna without a 0.2 cap or resistor (after a check the voltage was under 5VDC). Same results of no sound.

Quote:
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Try leaving the top cap connector on the 6L7 in place and clipping the output of the signal generator to it.

Lawrence.
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Old 15th Jul 2020, 2:13 pm   #55
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Default Re: Another Hallicrafters Sky Champion S20.

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Is it possible to adjust T1/T2 using this method to move the 500+455 summation to be equal to 955?
If you are able to determine the frequency of the Local Oscillator you can use this to calculate the frequency the IF is set to. Subtract the received frequency from the Local Oscillator frequency to give the IF.
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Old 15th Jul 2020, 2:15 pm   #56
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Default Re: Another Hallicrafters Sky Champion S20.

You can receive AM broadcast signals but injecting an AM modulated 455kHz signal you get nothing and you've already tried sweeping the generator for a good distance either side of 455kHz and still nothing, bit of a mystery then.

EDIT: Post crossed.

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Old 15th Jul 2020, 2:17 pm   #57
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Default Re: Another Hallicrafters Sky Champion S20.

We've been round that loop several times. Looks like one of those cases where a set doesn't obey the laws of physics!
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Old 15th Jul 2020, 3:07 pm   #58
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Default Re: Another Hallicrafters Sky Champion S20.

I assure you I am just as perplexed. I nearly created a video last night to post here showing the radio receiving 550, 600, 800, and 1300 kHz signals from my generator and then set the generator for 455khz, put it on the 6L7 cap, set receiver for 1800khz (as per the alignment instructions) and hear NOTHING.

I am lead to believe that taking off the stator from the 6L7 and directly injecting a 455khz signal into it directly resonates the coil at 455khz. Being a modulated signal with a tone, the rest of the radio is supposed to strip the audio portion out and send it to the AF section to go to the speaker.

What bakes my noodle on this is that if I can get the signal on the set at or near the signal generated frequency that tells me the oscillator (just one of course) is working at the correct frequency.

Bear in mind this effect of detecting the tone at the correct place on the radio is AFTER I tune it manually by ear to the 1350khz local station so it comes in strong. By this I am thinking that just because I can tune in a couple of local stations successfully does not mean the set is properly set to operate off of 455Khz (I may be wrong on this assumption).
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Old 15th Jul 2020, 3:13 pm   #59
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Default Re: Another Hallicrafters Sky Champion S20.

Long before I got to aligning the IF I went through the set carefully following the circuit diagram with an ohm meter. at the same time checking resistor values, valve heaters etc.
I started at the power supply and worked through the whole set.
You radio seems to be in much better condition than mine was. It had sat in the back of a shed for close on 30 years and had the original speaker, headphone connections, audio transformer and chokes removed. also it had been converted to a solid state psu. Despite its poor condition all of the circuits were true to the diagram. Without casting any aspersions on your ability, is is possible there is an incorrect connection somewhere when you did the resistors and caps? I know from bitter experience that this is possible! It seems very strange that an injected IF tone cannot make it through.
My method is simple I sit down with a copy of the circuit diagram and trace with a marker pen when a line in the circuit checks out.
Perhaps start with the signal path that the IF takes when connected to the sig gen. If you have a signal tracer this could be even easier following the tone through the set.
You have a collection of radios that I can only dream of and I am sure you will conquer the problem, then there will be at least two S20's in the world that are working.
If you ever come across any basket case examples of this set grab them with both hands. I am still looking for a tuning mechanism for mine.
Good luck
Lynton
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Old 15th Jul 2020, 3:54 pm   #60
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Default Re: Another Hallicrafters Sky Champion S20.

Your statements and questions are quite fair to ask

On the scale of devices I have designed, built, and worked on - this one is certainly on the low complexity side.

When I got it the set was completely stock (see pic of the underside) and I created a cap replacement list from the Riders documentation and what I saw in the set (common values). I did have the 600Ohm resistor on the 6L7 go up in smoke and then I replaced ALL of the resistors.

I did this one at a time: clip it out, locate it on the schematic, get the value and replace it with a firm connection to the old location. I have done this basic methodology with computer repairs, industrial device repairs, and guitar amps/stereos (technician 101 stuff).

I did trace the areas of the circuit against the schematic sufficient to determine I replaced what was there previously correctly. Since the set did not appear to be hacked in any way I did not particularly scrutinize it as potentially wrong. My SX-43 was a different deal - while it was 98% stock in parts, there were several instances where a repair or modification done decades ago prevented the set from ever working. Lots of complexity and error modes within that and many loose ends to contend with. But for the most part it ended up like 99% of the other devices I repair (fixed, fully functional).

The Dr Who radio I have is the exception: I guess I am looking for someone much smarter with radio repair to say "that symptom means 'X' is wrong". I can generally do that with any Marshall or Fender amp out there - even sight unseen sometimes because I have repaired and worked on so many over the decades.

In doing production repairs over the years, I have found that the most likelihood reasons are the causes for issues more often than not. I just do not have that 'sense' for radio gear at this time as my first radio project was the SX-43 last month. So I don't have too much to draw on as intuition can be a valuable tool. As an engineer I struggle with relying on non-measurement and non-factual evidence but systems can operate in strange ways (such as trying to diagnose and fix a parasitic oscillation in a complicated guitar amplifier).

If manually aligning the radio (by ear) as a substitute for a proper setting of the 455khz remotely works then the interoperation of the RF-->Mixer-->IF-->detection seems to be broken in getting the audio section something to turn into an audible tone.

Ergo: The signal going into a "redneck aligned" radio can pull a station or two but injecting a 455khz signal doe NOT work seems to be a clue what's not functioning (and now is turning into a quest to understand why).

All of your advice is helping and I appreciate all of the time and effort. I will return the favor by providing the reasons for the failure as to help others that may have this same strange radio set situation.

Quote:
Originally Posted by LyntonP View Post
Long before I got to aligning the IF I went through the set carefully following the circuit diagram with an ohm meter. at the same time checking resistor values, valve heaters etc.
I started at the power supply and worked through the whole set.
You radio seems to be in much better condition than mine was. It had sat in the back of a shed for close on 30 years and had the original speaker, headphone connections, audio transformer and chokes removed. also it had been converted to a solid state psu. Despite its poor condition all of the circuits were true to the diagram. Without casting any aspersions on your ability, is is possible there is an incorrect connection somewhere when you did the resistors and caps? I know from bitter experience that this is possible! It seems very strange that an injected IF tone cannot make it through.
My method is simple I sit down with a copy of the circuit diagram and trace with a marker pen when a line in the circuit checks out.
Perhaps start with the signal path that the IF takes when connected to the sig gen. If you have a signal tracer this could be even easier following the tone through the set.
You have a collection of radios that I can only dream of and I am sure you will conquer the problem, then there will be at least two S20's in the world that are working.
If you ever come across any basket case examples of this set grab them with both hands. I am still looking for a tuning mechanism for mine.
Good luck
Lynton
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