Another Hallicrafters Sky Champion S20.

[Station X]

1uuF not 1uF.

[mrrstrat]

Good catch! My mistake

I concur on the identify of this wire: it must be the 1uuf gimmick wire. Thanks for the sharp observations on this and helping me out

[mrrstrat]

This is is where I originally found the wire at. I attached a piece of vintage cloth insulated wire I have to lengthen it a bit and then wrapped it once around this grid wire it was on when I found it. I trimmed it similarly in length and bent it back out of the way (it is only wrapped once around the wire despite looking like two wraps.

This makes sense to me why I could not find evidence of where it went: this is because it apparently belonged here the whole time.

I found lots of little things that were more obviously wrong with my SX-43 and was able to correct it: this radio works fully and is a great radio now. I am hoping - like the OP of this thread I have hijacked - to get my somewhat rare S20 up and running.

This board is most helpful and I hope any and all information in this thread helps chronicle some of the unknowns of this particular Hallicrafters radio.

[ms660]

If that's the gimmick capacitor it looks to be coupled wrong to me, should be coupled into the wire loop that's connected to pin 3 (the anode) of the IF amplifier (the 2nd 6K7) you can see the loop that's connected to pin3 of that valve with nothing coupled into it in the photo's.

Lawrence.

[mrrstrat]

Extraordinary sharp eye: I was thinking it was on the grid wire (suppressor #4) of the 6K7 that is part of what is connected to the ganged capacitors. But it may have been on the pin #3 wire - I did not remember exactly but re-wired it on what seemed most logical with my limited radio knowledge.

So I can move this - when I took it off it was merely wrapped as it was originally looking like it was looped out of the way and then cut leaving a little 1.5 cm tail of wire.

By second 6K7 do you mean the one that is in the same tube column as the 6J5, 6L7 that are along the ganged capacitor tuner or the lone 6K7 that is in the middle of the set coupled to an IF can?

[ms660]

Originally Posted by mrrstrat

By second 6K7 do you mean the one that is in the same tube column as the 6J5, 6L7 that are along the ganged capacitor tuner or the lone 6K7 that is in the middle of the set coupled to an IF can?

It's the one that's between the two IF transformers, the BFO should be injected at the anode of that valve as per the schematic.

Lawrence.

[G6Tanuki]

With the coming of SSB in the 1940s/50s, BFO injection was often 'fiddled-with' because with a 'classic' diode-detector you needed more injection to ger acceptable results than had been the case back in the days when a BFO was only used for CW/Morse reception.

To quote Tom Jones, "It's Not Unusual" to find that in older receivers the BFO injection-point (and/or the size of the capacitor coupling the BFO to the IF/detector) have been messed-about a bit as an attempt to get better SSB reception. Sometimes this made things better, sometimes it made things worse.

[mrrstrat]

I placed the gimmick on the middle 6K7 and took off the first IF can to see if everything was good. The transformer in it tested NOT shorted and had a typical resistance between the three wires I would expect (4-6 ohms and some change). It was a little off-centre and I corrected it and tightened up the main bolt - I was hoping that was part of the problem (maybe touching something and grounding out?).

I plan to pull the other one off tomorrow and examine it inside and out. I did notice that one of the screws in the BFO can are missing - so that one will come off for re-examination as well. Maybe it just needs a small screw for it.

So a small run down of the strange and apparently paradoxical functions of the radio:

- Radio does not hum - nice and quiet (I rebuilt everything caps and resistors). It was mostly quiet before the rebuild as well.
- A calibrated and known to work signal generator signal cannot be found at the frequency radio dial is set at
- 1500 khz on the radio dial can detect about a 14MC modulated tone from signal generator (IF tuning makes the tone louder and quieter as one would expect).
- I can tune the first IF trimmers manually to pull in two local stations that are very strongly broadcasted - and they sound great though a lower volume than I would think it should be. The trimmers on the inside of the set for AM for osc, mixer, and antenna make the station come in louder.
- All SW bands apart from AM are quiet (dead?) - I cannot get anything no matter what I try.
- Tuning the second IF can appears to do noting to reception of the stations - even different parts of the AM band.
- With or without the IF manually tuned to receive the two local radio stations I can receive I cannot detect a tone from a signal generator at those same frequencies. How or why I don't know - it does not make sense. So I can tune a 1450khz station at about 1525 on the dial but a sweep of 1300-1600 from my SG produces NO tone. Also a sweep of all frequencies for AM band cannot be picked up on the AM band (most unusual).
- Injecting a 455khz tone as prescribed in the alignment process produces no tone, no discernible voltage change anywhere I have looking in the radio (with a DMM and a scope).
- When I got the radio - and before any rebuild - I was able to receive the two stations I can now get. While they sound much better and stronger I am thinking the radio is much more capable than to only receive the two strongest stations in my area that are 10 miles from my house.

I have built, maintained, and repaired Marshall amp clones, Marshall amps, Fender clones and most of the Fender amps made in the last 50 years so I do know how to diagnose and debug those circuits. I did this for about 15 years and do so for small repair projects these days. This radio is a real stumper as my SX-43 I just restored was a basket case and I spent three weeks fixing, upgrading, replacing, fabricating and alignment was the easiest part - everything worked and the complexity was much more than this S20.

I do appreciate help with this and am hoping this will help someone else working on a similar radio (if not this very model).

[mrrstrat]

That makes perfect sense. This radio is 83 years old and has had plenty of time for someone to attempt to tweak it. I have a more proper BFO mechanism in my SX-43. So that one and the SX-42 I had as a kid are my barometer for how SSB functionality are supposed to work.

I get from what you are saying I might be disappointed when everything gets working

[Station X]

Originally Posted by mrrstrat

1500 khz on the radio dial can detect about a 14MC modulated tone from signal generator

What exactly is a 14MC modulated tone? You terminology is all wrong. You need to inject an RF signal, 1500kHz for example, which is modulated with a tone, 400Hz for example.

So I can tune a 1450khz station at about 1525 on the dial but a sweep of 1300-1600 from my SG produces NO tone. Also a sweep of all frequencies for AM band cannot be picked up on the AM band (most unusual).
- Injecting a 455khz tone as prescribed in the alignment process produces no tone, no discernible voltage change anywhere I have looking in the radio (with a DMM and a scope).

That makes no sense. If you can receive a station on 1450kHz you ought to be able to hear the modulated signal from a signal generator at the same or close dial setting.

What is a 455kHz tone? See my previous comment.

Are you absolutely sure that when set to 455kHz, with the modulation turned on, your SG produces a modulated signal at a good level on 455kHz? Try your SG on the IF strip of another radio.

You need to successfully align the IF stages before moving on to RF alignment.

[mrrstrat]

My radio terminology might be wrong: when I set my signal generator at about 14MC and have it set for producing a modulated tone, it appears around the station I can tune that is around 1450khz. If I set the signal generator at around 1400khz I cannot find this tone even if I sweep the radio dial across the entire working range of band 1 (normal AM radio band).

The signal generator does work, has been restored, calibrated by a previous owner. I used it on my SX-43. If I set the signal generator for 1300kz, I can pick it up at 1300kz on my SX-43 as well as any other frequency both can set/recieve.

Again, the 455kz signal - modulated - cannot be heard when I inject this signal into my 6L7 as per the alignment instructions.

I am able to - for whatever reason - find the two strongest stations in my area by manually messing with the first IF can trimmers. It was by accident I discovered the radio was able to receive the two stations. When I discovered this, I set my signal generator for the stations approximate frequency to see if I could get a tone out of my signal generator at or near where I got a station to work. I did this when restoring my SX-43 - I could not verify the accuracy of the main/bandspread across all bands any other way to check my alignment and setup of the set.

I do agree that the alignment must be completed in stages: the first step I cannot do because I do not hear a tone to align to. I did take this first stage IF can apart last night and it did not appear out of the ordinary. I plan to look at the second in just a little bit this morning.

It does not help to have the tantalizing functioning of the radio in that I can receive an AM station I normally listen to and it is sharp and crisp (but not as loud as it should be). This is what confuses me as something is working correctly but I have not worked with these type of circuits enough to know what this anomaly behavior means.

The information on this forum has been invaluable in trying to get my arms around what is going on and will certainly make sure the root cause is found, corrected, and communicated

[Station X]

Originally Posted by mrrstrat

My radio terminology might be wrong: when I set my signal generator at about 14MC and have it set for producing a modulated tone, it appears around the station I can tune that is around 1450khz.

Are you saying that with your Signal Generator set to 14MC, which I assume means 14 Megacycles (Mc/)s or 14 Megahertz (14 MHz), you receive the signal with the receiver tuned to 1450kHz which means 1450 kilohertz?

[mrrstrat]

Yes, apparently that is what is happening. It may be a relative harmonic I am receiving on the radio because is it in such bad alignment and bad operational state.

What is interesting is that the two stations I am getting that are around 1300kz are the only two I can receive on the set. I have tried to apply the AM band alignment procedure w/o being able to receive an audible tone by fiddling with the trimmers used in the alignment. Believe it or not I have had limited success doing this with other radios though obviously not perfect or what we would call aligned. I cannot seem to do this with the S20 I have.

My theory on what is going on is that the set has a single issue causing the alignment to work in such a way that only a narrow portion of the sets capability "works" and is the result of the issue preventing proper alignment. My tuning one station is has apparently allowed the set to "work" for the two stations that occupy the same portion of the AM band. I eliminated wiring, bad connections, lead dress, bad tubes, and incorrect values of components from the equation.

On that thread, I am verifying that the oscillators are working properly: my only real experience building an oscillator device was a Hartley oscillator all tube theremin some years ago. So I am focused on the IF cans for today.

I am nearly at the point that after this exercise I plan to send the set to Space-X and have them jettison it toward the moon on the next planned launch if I cannot get it to work.

[Station X]

If you can receive broadcast signals around 1300 kHz, there's no reason why you shouldn't be able to receive similar signals from your signal generator. That applies regardless of whether the receiver is faulty and no matter what the mechanism by which the receiver is receiving 1300kHz broadcast stations.

I don't see a lot of point in checking the oscillators (plural?) until you've got the AF and IF stages working correctly.

If you inject an audio frequency tone at the volume control can you hear it from the speaker?

If you have a 'scope it shouldn't be too difficult to track a 455kHz modulated signal through the IF stages.

[mrrstrat]

I have not tried that but will as I really don't want to take the IFs apart unless it is absolutely required - there might be an issue in how the audio portion is demodulated from the signal within the set.

LATEST EDIT - SUCCESS: I can demodulate an injected RF signal at the tone pot. Now I am not sure what that means but I am thinking:

- A signal after the IF stages into the audio stage will properly demodulate the signal and extract the tone (a 455kz signal in this case).

So I probably need to pull that other IF can off and look at it. The first one - I have two IF transformer cans on the S20 - tested good from what I could tell. It did not measure OPEN and was not shorted out. The coil resistance was in par with what I might expect.

[Station X]

No need to take the IF (transformers?) apart unless you've proved they're faulty.

You should be able to display your SG's output on a 'scope and check how far it gets through the IF stages.

If the set can receive signals I'd say the IF stages are working, even if the IF is tuned to the wrong frequency. Swinging the generator's output would prove this.

[mrrstrat]

Hearing that tone from the AF stage lead me to that conclusion as well - thank you for that advice tidbit that stopped me from doing an IF-canectomy as this is a pain.

[mrrstrat]

I replaced the 0.002 domino cap I must have missed. Now I can tune SG to a frequency and reasonable get it on the dial as one would expect.

I *still* cannot hear a tone through the 6L7 when I inject a 455kz modulated RF signal through it. But little by little this radio is coming around.

[Station X]

Four posts deleted as new thread to be started in the Components and Circuits section.

Cannot move posts to new thread as they'll be out of sequence.

[mrrstrat]

Am I being evicted from this thread?