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Old 22nd Jul 2020, 1:33 pm   #81
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Default Re: Another Hallicrafters Sky Champion S20.

The seller was able to make it work - I am looking at the dimensions to see if I can actually take it out of the can it is in and put it into the S20 can. The trimmer screws look to be about correct and may lend itself to be a transplant.

I did consider having to drill a couple new holes worst case - since this is being sold as fully functional I am hopeful that my efforts will only be focused on installation.
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Old 28th Jul 2020, 4:01 am   #82
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Default Re: Another Hallicrafters Sky Champion S20.

So I got the new IF can - measured good, it was tested by seller, it fit like a glove in the old Hallicrafters IF can (Yes!!), wired in great. It fit into the original IF can and the new trimmers on the new transformer are in the exact position as the old ones.

And I got the same results...Low volume on channels, no audible tone from injected signal into 6L7.

So back to square 1 again with a GOOD IF can now
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Old 28th Jul 2020, 6:18 am   #83
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Default Re: Another Hallicrafters Sky Champion S20.

Elektrotanya has the S20 (NOT the "R" one) manual on their site.
Be sure to hit the "English" button and 'Translate".
Unless you know Hungarian, of course. HTH

Last edited by FrankB; 28th Jul 2020 at 6:19 am. Reason: more info
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Old 28th Jul 2020, 9:19 am   #84
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Default Re: Another Hallicrafters Sky Champion S20.

What voltage do you now have on the anode/plate (pin3) of the 6K7 IF Amplifier?

No voltage here would be a show stopper.

What voltages do you have on the various top caps?
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Old 28th Jul 2020, 1:03 pm   #85
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Default Re: Another Hallicrafters Sky Champion S20.

There very next thing to check - it just got too late to addresses it last night. But I did get it retro-fitted into the original IF can, checked for proper insulation and safety, and then wired in properly.

A quick test revealed that the burned out transformer may have been a symptom rather than a reason. Now comes follow the voltage and where it stops.

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What voltage do you now have on the anode/plate (pin3) of the 6K7 IF Amplifier?

No voltage here would be a show stopper.

What voltages do you have on the various top caps?
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Old 28th Jul 2020, 4:32 pm   #86
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Default Re: Another Hallicrafters Sky Champion S20.

Ok - following the wiring that was there I can see that the 6K7 voltage for the IF amplifier was never going to get power - I moved this wire and the other wires of the IF transformer to where the schematic shows.

Now the AVC works instead of going to nearly audible/no sound. The radio is louder and the two free-tunes stations come in much louder.

The newly built IF can appears to make the reception better when I move the trimmers and the IF stage 6K7 anode now shows in excess of 300 VDC.

I still cannot hear a tone from the 455khz RF signal injected onto the 6L7 - I might have better luck polling the mixer for a signal deflection increase?
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Old 28th Jul 2020, 4:44 pm   #87
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Default Re: Another Hallicrafters Sky Champion S20.

Quote:
Originally Posted by mrrstrat View Post
Ok - following the wiring that was there I can see that the 6K7 voltage for the IF amplifier was never going to get power - I moved this wire and the other wires of the IF transformer to where the schematic shows.
That suggests that the set has been modified or messed with at some time. If that's the case there's no telling what other wiring errors may be present. Perhaps someone tried to bypass the open circuit IF Transformer, we'll never know.

Quote:
I still cannot hear a tone from the 455khz RF signal injected onto the 6L7 - I might have better luck polling the mixer for a signal deflection increase?
Have you tried slowly tuning the signal generator from say 400kHz to 500kHz to see if you can get a response anywhere? You need to fix the IF stages before moving on to other tests.
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Old 28th Jul 2020, 4:55 pm   #88
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Default Re: Another Hallicrafters Sky Champion S20.

The alignment instructions call for a signal at the IF to be injected onto the control grid of the 6L7 mixer valve. If the 6L7 isn't working for any reason the signal won't get through. It'd be worth checking the wiring and components around the 6L7
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Old 28th Jul 2020, 4:59 pm   #89
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Default Re: Another Hallicrafters Sky Champion S20.

Sad but true with the set being messed with: its had 83 years for someone to mess with it. On a positive note the original caps and resistors were there, but only thus far a slight deviation from the schematic. The SX-43 I have had more 'creative engineering' but was limited in a few areas. I liken this to what I have seen in 20 years of fixing amplifiers where a wanna-be tech or adventurous owner changes components or wire routing to enhance something.

I did try a sweep but I guess I am not clear on what bypassing the first 6K7 (RF stage) does beyond making the transformer circuit resonate at 455khz. I can feed in a signal in through the antenna and find it in the general location on the radio dial. It DOES seem to work in the area I tuned in around 1300khz and gets faint to inaudible the father away you get from that area on the dial. I cannot pick up anything at 600khz but can get a very quiet tone at 800khx. At around 1000Khz it is loud enough to easily be found. At 1300-1400khz I can get it obnoxiously loud. Going toward 1800khz it drops off to inaudible before 1800 (meaning I cannot find a tone in that area - even sweeping the signal 1750-1900khz does not produce anything I can find. This of-course is where I am tuning the signal generator for a signal I wish to find across the radio's dial as if I am making a radio station to find with the radio.

Just to be clear: the OP in the other S20 thread told me he was able to inject the signal as per the alignment instructions and get the tone. I am taking a closer look at the layout but this point-to-point layout crap drives me nuts. A proper circuit layout is more what I am used to . I basically work from the valve pins to other valve pins using the schematic as a guide.

Quote:
Originally Posted by Station X View Post
Quote:
Originally Posted by mrrstrat View Post
Ok - following the wiring that was there I can see that the 6K7 voltage for the IF amplifier was never going to get power - I moved this wire and the other wires of the IF transformer to where the schematic shows.
That suggests that the set has been modified or messed with at some time. If that's the case there's no telling what other wiring errors may be present. Perhaps someone tried to bypass the open circuit IF Transformer, we'll never know.

Quote:
I still cannot hear a tone from the 455khz RF signal injected onto the 6L7 - I might have better luck polling the mixer for a signal deflection increase?
Have you tried slowly tuning the signal generator from say 400kHz to 500kHz to see if you can get a response anywhere? You need to fix the IF stages before moving on to other tests.
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Old 28th Jul 2020, 5:10 pm   #90
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Default Re: Another Hallicrafters Sky Champion S20.

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Originally Posted by mrrstrat View Post
I did try a sweep but I guess I am not clear on what bypassing the first 6K7 (RF stage) does beyond making the transformer circuit resonate at 455khz.
The IF transformers T1 and T2 should always resonate at 455kHz. Bypassing the 6K7 RF stage does not make them do so.

The reason for injecting the 455kHz signal at the mixer rather than at the aerial socket is because otherwise the signal would otherwise have to fight its way through aerial and RF stage coils which could be resonant anywhere between say 500kHz and 30Mhz depending on what waveband was selected and how the tuning dials were set.
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Old 28th Jul 2020, 5:29 pm   #91
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Default Re: Another Hallicrafters Sky Champion S20.

Another suggestion.

Unplug the 6J5 local oscillator valve. If the set stops working, ie you can't receive signals anymore, you'll know that the set has been operating as a superhet.
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Old 28th Jul 2020, 6:28 pm   #92
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Default Re: Another Hallicrafters Sky Champion S20.

I am listening to the set now: I did test pulling the 6J5 (not the BFO one) and then turned it back on: no stations received - the set stopped working. So it is super-het'ing.

When I replaced the caps (many weeks ago) I did notice that a 0.1uf was where a 0.05uf should have been on the cathode of the 6L7. I did just replace this and it seems like I got more tad more volume but not able to detect a tone from a 455khz modulated signal. I am using my Hickok signal gen that is extremely accurate (and works). I checked it with my frequency counter as well.

I am convinced the 6L7 is true-to-schematic now.


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Another suggestion.

Unplug the 6J5 local oscillator valve. If the set stops working, ie you can't receive signals anymore, you'll know that the set has been operating as a superhet.
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Old 28th Jul 2020, 6:39 pm   #93
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Default Re: Another Hallicrafters Sky Champion S20.

Thanks! This clears up my observations and misunderstanding. Based on this the set should be able to pull out the tone (modulated) out of the signal without being tuned to that frequency on the dial.

This makes sense why I cannot hear it (though not a cause). I can tune my SGs (either one) for about 1355khz and easily find it on the dial when I go through the antenna and tuner. But when I deviate the tuning below about 1100khz or above 1600khz I cannot hear the modulated tone through tuning the set (when the signal is injected through the antenna). I have been treating the signal gens as a 'station' to find and seems to only work in a narrow band on the dial. Since the 455khz RF signal is well outside of that I simply cannot hear the modulated tone because the set seems to only like frequencies centered around 1350khz.



Quote:
Originally Posted by Station X View Post
Quote:
Originally Posted by mrrstrat View Post
I did try a sweep but I guess I am not clear on what bypassing the first 6K7 (RF stage) does beyond making the transformer circuit resonate at 455khz.
The IF transformers T1 and T2 should always resonate at 455kHz. Bypassing the 6K7 RF stage does not make them do so.

The reason for injecting the 455kHz signal at the mixer rather than at the aerial socket is because otherwise the signal would otherwise have to fight its way through aerial and RF stage coils which could be resonant anywhere between say 500kHz and 30Mhz depending on what waveband was selected and how the tuning dials were set.
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Old 28th Jul 2020, 6:46 pm   #94
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Default Re: Another Hallicrafters Sky Champion S20.

I don't think I can help you any further with this.

If the set is operating as a superhet, which apparently it is, you should be able to pick up the local oscillator on a second receiver, but you can't. Also you should be able to get a signal at some frequency through the IF stages, but you can't. This defies any logical explanation that I can think of.

Offering advice in the forums can be competitive at times, so perhaps another member will be along to assist you and will demonstrate what it is I've missed.
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Old 28th Jul 2020, 8:25 pm   #95
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Default Re: Another Hallicrafters Sky Champion S20.

And not a waveform in sight that's worth mentioning.

Lawrence.
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Old 28th Jul 2020, 8:44 pm   #96
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Default Re: Another Hallicrafters Sky Champion S20.

Worth a try. BFO might be the place to start to prove the scope's working.
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Old 28th Jul 2020, 8:55 pm   #97
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Default Re: Another Hallicrafters Sky Champion S20.

I would want to see the sig gen connected to the mixer grid as per the manual and set to the correct IF with the 'scope connected to the mixer grid as well so as to verify amplitude and frequency as applied and take it from there.

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Old 28th Jul 2020, 9:02 pm   #98
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Default Re: Another Hallicrafters Sky Champion S20.

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Old 28th Jul 2020, 10:33 pm   #99
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Thumbs up Re: Another Hallicrafters Sky Champion S20.

I ran out of time on it today. I did the above with my SX-43 - the scope helped me a lot with that one. I am beginning to think I have a set that was part of the USA compulsory disablement of S/W.

I have only heard of radios with shortwave disabled during WWII but never saw one. The age for such a set fits mine but I can hardly believe as much as it cost in 1938 someone would have let a repair person disable it (seems very unlikely). I have been too tied up to roll my sleeves up on this one (and hoping someone gives me the magic bullet solution). I didn't have help with the other one and figured it out - so let the deep dive into this set begin .

As I can peel time away to work on it, next step is to see what the BFO/Oscillaros are doing.

Thanks all for advice on this set
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Old 29th Jul 2020, 9:51 am   #100
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Default Re: Another Hallicrafters Sky Champion S20.

Even if shortwave were disabled medium wave (AM in the USA) would still have had to work or the set would have been useless.

That means that the IF stages and local oscillator would have to work. We keep coming back to that.

You said early that adjusting the trimmer screws of the new IF transformer improved reception. That points to the IF stages working.
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