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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Mon 14, 2021 5:49 pm 
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Location: Edmonds, WA USA
How do you know that your Heathkit Oscillator has output and if so, at what frequency? Does it out a modulated signal? What model is it?

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Mon 14, 2021 7:17 pm 
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It is a Heathkit IG-5280. It worked when I did an alignment on another radio a couple months back. It has a dial on it to tune to the necessary frequencies as outlined by alignment instructions on radio schematics.

I could very well be using the wrong tool, but this is the only one I have where I can tune to the frequency needed to be injected into the radio. It does have two trimmer posts on the front: the one on the right has “amplitude” labeled above it, the one on the left has “amplitude” above it, and “% modulation” below it.

Please do tell me if I am in need of a different tool. The diagnostics I am undertaking now (with you, Bob, and Jthorusen assisting me) are becoming more and more unfamiliar to me. I don’t think I had to go this far with any radio diagnostics before, so I could be under equipped in this manner.

https://images.app.goo.gl/jH4yjGnV8wmuAbYF7

I am away from my testing equipment at this time, so I linked a picture of it here.

Thanks,
Forrest


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Mon 14, 2021 7:26 pm 
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Joined: Jan Tue 10, 2012 8:39 am
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That is a very simple signal generator. It should be able to provide the signal you need to troubleshoot the radio. The rf output is either unmodulated or can be modulated by the audio generator at 1 kHz.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Mon 14, 2021 9:09 pm 
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If you are concerned about the signal generator, test it the way you tested the radio using your Zenith Transoceanic. Place a test lead connected to the signal generator red RF output near the antenna of the Zenith. Turn on the modulation and advance the knob about 20%. Turn the generator frequency to about 600 KHz and try and tune in a tone near 600 on the Zenith. Turn up the RF amplitude full if you hear nothing. If you get a quiet spot at 600 and no tone, turn up the modulation. If you still hear no tone, then the generator is sending an unmodulated signal. How close to 600 KHz you hear the signal generator should tell you whether it is off frequency when you go to set it at 455 KHz. Ideally you want the generator as close to 455 KHz as possible, so getting a good feel for the accuracy at 600 or 540 or as low as you can with the Zenith will allow you to calibrate the generator for 455 KHz.

Norm

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Mon 14, 2021 10:46 pm 
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A more accurate method is to listen for the second harmonic, at 910 kHz.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 12:55 am 
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Tuned to 600 kHz, I was able to pick up the harmonic signal at 575 kHz on my Philco 41-250 (the Zenith wasn’t picking it up for whatever reason).

The Philco was fading in and out on volume. I think one of the tubes may be damaged due to vibration from an external speaker in the family room.

Regardless, the meter is only off by about 25 kHz, so I reckon I tune it to compensate, right?

Thanks,
Forrest

EDIT: It’s not a damaged tube, it’s just that some of these tubes are nearly dead. Strange, this radio is (by leaps and bounds) my BEST receiver, to the point where I can pull in signals from Budapest and Beijing just sitting inside with the internal antenna in use.


If only Philco made boat anchors...


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 1:32 am 
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Yes tune it to compensate.

Norm

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 2:11 am 
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Having now tuned my RF Oscillator to 480 kHz (to compensate for the 25 kHz difference between dial tuning and RF output), all I receive is static pops in both V4 Control Grid and V3 Control Grid.

Still no harmonics. Does this mean that the problem is with V3 or V4? I’m assuming that it does. Again, I’m feeling around in the dark, so I could be way off the mark.

Thanks,
Forrest


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 3:39 am 
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Greetings to Forrest and the Forum:

I've sort of lost track of the signal generator tests. When tuned to a frequency that can be received by your test receiver, is there tone modulation present or not? If there is no modulation, then you will hear nothing but pops and static when connecting your generator to the IF strip.

If you are sure that your signal generator has modulation and plenty of output (best checked with a decent scope... do you have one?) then using a coupling capacitor of .01 or so (always use a coupling capacitor as has been mentioned; never connect the signal generator output to the device under test directly), connect the signal to V4's plate. You should get a tone in the speaker (if the volume control is turned up). If you don't get a tone here, then connect the signal generator to the 6H6 pin 5. Here, you should hear a tone if the signal generator output is high enough in level.

It is possible that since you re-worked the IF cans to eliminate silver mica disease, then the IF's may be so far off frequency that they pass no signal near the designed IF frequency. Here too, a good scope and a reasonably well calibrated signal generator would be of great help in narrowing down the difficulty.

Please let us know what you find when you try injecting signal at the above points.

Good Luck,

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 4:59 am 
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After following this exchange for some time, it makes me want to go over there and do some testing myself. I feel I can nail the problem in the first 5 minutes. It's very cumbersome to help someone in a forum, especially when you have to describe the setup in excruciating detail.

My own history is somewhat mixed, as I have burned out stuff and broken things in my enthusiasm to get the job done. I certainly didn't err on the safe side much of the time.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 5:55 am 
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Greetings to Bob91343 and the Forum:

I've often wished for a package containing a good test equipment suite, plus a stereo camera and a set of remote manipulators equipped with the usual hand tools including soldering equipment. One could ship this package to someone requesting help or restoration in their area, due the job using telepresence via the internet, and then ship the system on to the next person.

If you can design and build such a system that has all the capability needed, is robust enough to be shipped all over the place and is light enough that the shipping charges won't break the bank, it would be great. I for one would even kick in a few bucks.

However, I'm not going to hold my breath. :D

Regards,

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 6:27 am 
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Don't hold your breath, but still that sort of scenario is not out of the question. If we can have self driving cars, that's a big step toward nirvana.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 8:11 am 
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"After following this exchange for some time, it makes me want to go over there and do some testing myself. I feel I can nail the problem in the first 5 minutes. It's very cumbersome to help someone in a forum, especially when you have to describe the setup in excruciating detail."


Boy, what I wouldn't give for this. This is by far the longest thread I've ever created, all for a problem that, most likely, could be very easily solved in a few minutes.

I do want to say a sincere thank you to all of you thus far. The help you have given me is immeasurable, and I have learned quite a bit in these exchanges. Information that I am sure I will use well beyond this radio.

I am most grateful.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 3:59 pm 
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As much as the experienced radio troubleshooter would like to resolve these repairs quickly and efficiently, it is the long, painful, wandering restoration--that actually teaches the most. Stick with it and you will be rewarded.

Norm

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 5:43 pm 
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It is true that the most profound learning comes from bootstrapping oneself from ignorance to experience. Another method, perhaps not as good, is to stand by and watch as an expert does the job, while explaining the procedure and answering questions. And even handing over the tools and directing their use.

The last part reminds me of when I tried to replace the memory battery in a spectrum analyzer. I had to pop loose some plastic standoffs that held a board that was in the way. I couldn't get it apart and decided to put off the job rather than risk breaking the board. But I knew I wsa close to breaking it and wisely backed off in my efforts. A beginner wouldn't know the limits.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 6:52 pm 
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To answer Jim’s question from a few posts above, yes, I do have an oscilloscope, though it is more basic. It’s a Tenma 72-720. I am not well acquainted with oscilloscope usage because it’s nothing I’ve ever needed until now. Still, I attached the oscilloscope probe to the coupling capacitor of the RF Oscillator, and the trace line wasn’t moving very much. I’m sure that has more to do with my lack of knowing what to do with the scope (and it’s various settings) as opposed to equipment failure, so I’d much appreciate any advice on how to properly measure the output of this Oscillator using the Tenma.

Thanks,
Forrest


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 7:46 pm 
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Don't give up, the guys here are great and will work thru it with you. I love the idea of a remote control device that can be operated by one the many experts here. That's a great idea. What I did when I was starting out was watched craigslist for a simple AA5 tube type radio that was cheap. They made millions so they are still pretty easy to find cheap. I then went thru that thing backwards and forward and really learned how each section worked (there are many writeups on the web and they are all made about the same). And more important why each section is needed.
After I really understood how each section worked and sent the signal to the next section, a lightbulb went off. Now most receivers are basically the same, they just might have more sections for better selectivity, but still they are just "sections".

Follow the signal thru that radio. Signal always comes in on a grid and out on the plate. Use a signal tracer to follow the signal thru the radio. Start at the front and work your way thru it. Measure the resistance of the coils in the front end. Open coils are easy to spot and will make the radio deaf. If you are lucky enough to have a manual that lists the values for resistance and voltages at each tube base, record all these and find where it's different. If the voltage is low, look for a shorted cap or resistor that has a really high value. If the voltage is higher than expected look for an open device ie no load on power supply. Once you get thru this, then try and find the signal on the grids of each section. If you have a signal before the IF transformer and no signal after, then the problem might be an open coil or an open cap inside the IF can. Just use logical approach and before you know it, you will find the issue.

Sometimes you can't figure it out. I have parked radios after I could not figure out and then a few years later when I knew more I figure them out. Always check that somebody before you didn't make a wiring error ie connection of a wire to the wrong pin of a tube. That S-40 is over 50 years old and who knows how many hammy hamfisted hambones had their booger hooks into it before you. There could very well be a wiring error. The voltage and resistance chart might show that as well. And one more thing, don't forget this is fun. Sometimes I get frustrated and forget that. Taking a break and working on a different rig, or doing something different can make all the difference. I have taken a break on something and when I get back to it, the problem is plain as day. I could not believe that I missed it.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Tue 15, 2021 8:08 pm 
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Ultimately, I may have to park it. I want to better understand my oscilloscope before I do though :lol:

It is starting to become a dime holding up a dollar scenario. I have an RCA T80 that I’m going to restore and sell to my brother once I’m done with this Hallicrafters. It is starting to weigh on me that this profit is being held up by some genius’s fiddling with the radio (the fact that someone was in there before me was painfully obvious). Truth be told, someone was in that RCA too. There’s a stick of Electrolytics soldered underneath the radio for whatever reason. Either way, it IS a simpler radio, so I should be able to work out the bugs (should there be any) with out this much fanfare.

Plus, this S-40B is a single conversion, crystal-less radio, right? I’m certainly not knocking it because it is good for what it is. However, I could be taking what I’ve learned here and applying it to an SX-42, or an SX-71, I.E: something that is better equipped for serious HAM radio usage.

Not to get all sappy, but perhaps this was the reason I came across this S-40B in the first place: to learn what I have learned in this thread, both in terms of skills and mindset.

A lot of the time, it’s the journey and not the endpoint. I have to remind myself of that more often than I really should.

EDIT: I should add that I am not giving up on this radio. I’m going to run through as many diagnostics as possible, but I may put it on ice so I can get my eyes on something different and fresh and come back to it in a week or so.


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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Wed 16, 2021 12:49 am 
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Greetings to Forrest and the Forum:

Do you have the Tenma scope Manual? It is downloadable from the BAMA web site if you do not have it. First, perform the initial setup and checkout on page 2. Then you should be able to look at your generator output. You will need to use a fairly high sensitivity setting on the scope (low volts per division) in order to see the output of the generator. Use a slow sweep speed to see the modulation envelope; use a higher speed to see the RF sine wave. Use AC coupling.

Once you have the generator wave form displayed, you can then inject into the IF and look at the output with the scope. If, for example, you inject at the plate of V4 and look with the scope at pin 5 of the 6H6, you should see more or less the same waveform. If the generator is set to the correct IF frequency, you can try adjusting T3 for maximum amplitude of the scope display. Alternatively, you can move the generator frequency up and down and see where T3 is actually resonant. If it is nowhere near the correct IF frequency, this could be your difficulty.

Good Luck,

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 Post subject: Re: Hallicrafters S-40B- Audio Completely Dead
PostPosted: Jun Fri 18, 2021 12:07 am 
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I was able to see the RF sine wave of the RF Oscillator on the scope. I’m assuming the modulation pocket is the vertical line that moves slowly across the screen at a low sweep speed (I have mine set to 50 mS). Assuming that it is, I also see that as well.

I should connect a coupling capacitor to the Oscilloscope probe, right? I don’t know if that would mess up it’s ability to read incoming signal, but it seems like the safe thing to do.

Assuming that everything I typed here checks out, I’ll get started on testing.

EDIT: I should note that the RF sine wave is rather fuzzy. I can’t get it any more clear than that. Does that mean something?


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