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 Post subject: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Tue 06, 2018 6:15 pm 
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The other day I was doing some touch up alignments on the SX-117. The 80m slug is either stuck or more likely the proper General Cement tool is slipping and I cannot get the slug to move. I've tried some other adjustment tools and they slip too. I'm a bit anxious about using an Allen wrench or the like fearing I will "round-out" the hole or possibly crack the slug. Any suggestions?

thanks...harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Tue 06, 2018 6:25 pm 
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Harry,

The slug may already be cracked, that is a common cause of it being stuck. It may well have happened long before it was sold to you.

One thing that sometimes works is to put an Allen wrench in the slug and apply heat to the wrench via a soldering iron and then try to gently rock the slug to free it. If the heat is going to work it will do so in about 20 seconds, no need to cook the coil. Be sure to use pliers for the Allen wrench so as not to brand your hand.

If the slug is cracked the best thing to do is encourage it to finish falling apart, remove the debris, and replace with another slug. If the internal threading of the coil is messed up you can use the alternative method seen in a number of rigs where the core is suspended by a wire from the top, it is lowered/adjusted to the proper position then then fixed with solder to a plate sitting on top of the coil assembly.

Good luck!

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Tue 06, 2018 9:46 pm 
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In the past, I have had a few of these problems. Once the old slug has been removed, I have taken that slug (or a new slug from Surplus Sales of Nebraska) and using either a cheap adjustment tool you don't mind ruining or a proper size long screw with nuts, chuck the slug up in a drill motor and turn it against some emery paper to slightly reduce the diameter. This can make it go back in the core more easily. A second option I have used is to pirate a slug that is smooth with a screw on the end from an old transformer. I then glue a nut to the top of the good transformer or coil can and position the slug that way. I guess the approximate volume of the old slug and cut the smooth solid slug to be close. It can be cut by chucking it up in the drill motor and turning it against a hacksaw blade.

Norm

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Tue 06, 2018 11:25 pm 
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Rodger and Norm,

Thanks for the suggestions.

I'm not convinced the slug is cracked...yet. I think the problem is the adjustment tool no longer fits the hex hole in the slug. If I shine light from underneath the assembly I can clearly see the tool is no longer snug. I had made adjustments before, but for some reason I can hear and feel the tool turning and slipping.

I'm going to walk away from this for a day or two and think about how to construct a tool that may fit. An Allen wrench may work, but given the cores are brittle I'm afraid of "rounding" the hole.

Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Wed 07, 2018 12:00 am 
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Ferrite is very hard material so it isn't likely to be worn but typical alignment tools are a fairly loose fit and are made of flexible material so they will slip in the core easily under higher torque loading. Be very careful that when applying force to the core that you don't rotate the winding tube itself or you will also have broken wires as an additional problem. You see this often with the Heathkit SB and HW series transceivers where the hetrodyne and other front end coils will pop loose under turning force and break the wires.

Supposedly one of the biggest cost drivers of the Hallicrafters SX-88 was the machining process for the ferrite used to produce its very high Q transformers and the lower cost descendants used fairly conventional transformers. Akai and Sony used ferrite composition heads in many of their reel to reel decks because of their excellent wear resistance. Fortunately with tape decks cracking a ferrite head would be a rare occurrence.

I assume the problem is with one of the hetrodyne oscillator coils and the safer fix may be leaving the core where it is and adjusting the value of the parallel capacitor; you could use a small trimmer plus the current or a different fixed capacitor from the stock one depending upon which direction you need to go.

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Fri 16, 2018 10:51 pm 
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Well I'm back....

Another ham and I gave this a long look today. It's apparent the 80m slug is stuck. Whether that means it's off the threading or something else is unclear. We tried various alignment tools as well as an allen wrench with no joy. We removed the 10m slug below it and that one is cracked. The lower piece of the cracked slug came out, but the remainder is stuck as well. Any attempt to twist the 80m slug is causing the coil form to move and we became concerned repetitive twisting may cause the coil form to become damaged.

So the most expedient approach is to replace the coil/slug assembly. If anyone out there has an L10 A/B for the SX-117 in need of a new home please let me know.

Thanks...Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Fri 16, 2018 11:25 pm 
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You are probably going to have to crack the other core to get it out in pieces and then you can use donor slugs. There are likely many ways to crack one of these but I use a very thin blade precision screwdriver with the blade edges near the coil form wall and the opening in the slug and give it a sharp tap. Ferrite is very brittle so it usually cracks easily. Others may have other favorite methods.

Another possible method is to use a straight blade screwdriver to try and turn the core because I suspect this is how many of them originally get cracked.

There are probably fragments of the cracked core stuck in the threads of the remaining intact core locking it in place.

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 2:52 pm 
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Rodger,

Thanks for the suggestion.

A few questions. Are all the cores in the SX-117 the same size? How challenging is it to find replacements? And finally, and I know this is going to be a silly question, can cores from other rigs be used and is there any "standard" regarding threading, ferrite material, etc.?

Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 4:23 pm 
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Harry,

I believe all of the cores in a section of the SX-117 will be the same size but I have never measured them.

There are different ferrite "mixes" used for different frequency ranges however in many cases you will find it isn't that critical so there is a good chance that a random replacement slug you find will work OK. Most of the slugs you will find came from other communications receivers and so there is a high probability that a slug you acquire will be OK if not exact. There are a few different common sizes and threads, you might be able to accurately measure one of the intact slugs but it is no guarantee the person having a potential replacement will have an accurate measurement.

Another possibility to get this receiver going while it waits for parts is to do a little "expedient engineering". If the stuck slug (or remains of a slug) is providing too little inductance you can insert a bit of ferrite material into the coil form to increase inductance. If the inductance level is too high a bit of brass inserted into the coil form will decrease it. A standard tool of many of the older complete alignment tool kits was called a "magic wand" and it has a slug of ferrite in one end and a slug of brass in the other; to use it you slowly inserted each end into the coil form and if neither end resulted in an increase in output then the alignment for that coil was optimal.

One of my Geloso rigs had a stuck core and while waiting to find a proper replacement I glued a small piece of scrap ferrite material to a toothpick and varied its depth in the coil form for a peak and then used some molten wax to hold it in place. That allowed me to finish restoration and I used the transmitter for another year until I finally found a suitable replacement. Consider doing a reversible temporary repair like this if you have difficulty finding a proper replacement so that you can enjoy the rig instead of having it lying in pieces on the bench waiting for one or two parts. If the inductance is too high then do this same trick with a small brass nut or washer.

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 5:47 pm 
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Harry,

I don't have the SX 117. I do have a HT 44 and the SR 160 which are from the same period and style of radio as the SX 117. My radios have coils on 1/4 ID phenolic forms. The forms are pretty fragile. There is no threading on the inside of the forms. The ferrite slug has threads which engage a waxy coating in the form to stay in place. This to my knowledge is the way all of these are done. Surplus sales of Nebraska sells threaded 1/4" slugs that will fit these forms. There are several lengths, but it isn't critical. Get approximately the same size slug. They are inexpensive, so buy a variety. A larger slug will just not be screwed as far in. As I said earlier, a person can take a slug and use a threaded machine screw and some nuts or an old alignment tool and mount the slug in a drill and then turn it against some emery paper or a file to reduce the diameter a little to fit a problem core.

Getting the old slug out is the hard part. Some people suggest using a warm air gun to heat the coil slowly and evenly until the waxy inside coating softens and the slug can be removed. I would try a long, small diameter machine screw fed through the center of the slug and a nut then turned down to grip the slug. That may give more purchase to turn the slug. The real danger is that you damage the form, so just don't force anything.

These are pretty simple solenoid style coils. You could easily make one to replace the 80 meter coil. Phenolic tube is available from McMaster-Carr. That and some magnet wire would do the job. Just measure the inductance of the old coil to see what is needed for the new coil. The ferrite slug enables a very wide range of tuning.

I am working on a Homebrew receiver and have a post in the Homebrew forum regarding coil winding where I show the inductance range with a ferrite slug in a coil I wound.

Norm

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 8:47 pm 
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Rodger and Norm,

Once again many thanks.

Apart from the 80m slug the only issues with the SX-117 is low signal on 20m and a finicky if not unresponsive S meter. When adjusting the crystal oscillator slugs per the manual all seem to peak around -10VDC with the exception of 20m where it peaks at about -7.

I'll take a look at Surplus Sales of Nebraska and order a few slugs. The 80m slug is in there quite tight. If held by wax I'm amazed this thing won't budge.

Thanks again,

Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 8:58 pm 
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Harry,

It isn't soft wax or the first time the radio was in a hot environment all the slugs would fall out. It is a harder type wax which over time turns into a varnish-like material. I have ripped off the coil form twice trying too much force and both times was able to repair my mistake.

I would not discount Rodger's suggestion to use another repair strategy if needed. A small diameter brass machine screw pushed down through the hole in the ferrite core would lower inductance or a steel screw would raise inductance. Either of these may allow you to adjust the coil. Then just leave them there. A wooden plug with a hole through it might fit inside the top of the coil and your new screw slug would thread through that and be adjustable.

Norm

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 9:32 pm 
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I think we will give this a shot sometime this week. It seems so simple to try.

Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sat 17, 2018 9:37 pm 
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Harry,

If you have another 12AT7 try substituting that for V3 to see if that increases the output on 20 meters. Sometimes a marginal oscillator tube won't play well with some crystals. Don't rely upon a tube tester because the performance that matters is when it is at its operating frequency and the tube tester doesn't come close to simulating that environment.

The S meter circuit is very simple in the SX-117. First make sure that the movement isn't sticking mechanically, it should move smoothly with the zero control. With the power off you might also run the zero control from end to end a few times to clean the wiper. Check R22 and R23 to make sure they haven't gone up in value. The setting of the factory gain control will affect both overall receiver gain and S meter response. The S meter tends to be a little stingy on this model but usually low S meter readings are from a lack of overall gain. Adjusting the preselector control should result in a noticeable noise peak with an antenna connected and with the RF and AF gain near max the noise should be quite loud. Make sure that the T notch filter is detuned so that it isn't in the primary IF passband.

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Feb Sun 18, 2018 12:54 am 
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since you're so far down the beaten path with this broken slug problem, I'll purpose another possible solution.

The "problem" of course, is that the slug has fractured, AND, any torque applied to the "pieces" simply expands those pieces and it'll never come out. So lets glue it back together and see if we can then get it out.

First, select a tuning tool thats NOT affected by acetone. A little on your finger, rub the tool, if the surface doesn't get gummy or start to dissolve, thats the one to use. Also don't use the type that can be slid through one core so you can tune the one below, I don't think they can apply enough torque to do the job.

Place a little puddle of the thin superglue on a piece of glass or metal. More or less, lay the tool on it's side and roll the end of the tool in the puddle so all the "flats" are covered, then quickly slip it into the broken slug, NO twisting the tool yet.

Capillary action should bring the adhesive onto the flats, and into the fractures in the slug.

Allow a few minutes for all the mixture to "cure", then see if the slug can be extracted.

If this works I'll send you a bill. :wink:

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Apr Mon 09, 2018 1:24 pm 
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Well, it's been a dog's age since I've gone back to the SX-117. Went over it the other day and came to the conclusion that any hope of fixing this coil and slug is going to require me to remove it and possibly rebuild or replace it. The hole in the 80m slug is rounded out and the slug itself appears to be lodged in there. I picked up some slugs and coils of various values from Surplus Sales of Nebraska. Whether the coils I bought are even close to the right value is going to require some research. In any event, I hope to start working on it later this week but have a question. If I need to build a new oscillator coil what type of wax do I use to adjust the slugs and keep them in place?

And by chance if anyone out there has the coil/slug assembly out there (L10 A&B on the schematic and Halli part number 051-003487) they are willing to part with I would be most appreciative.

BTW, the receiver works nicely on 40m and up!

Thanks...Harry


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Apr Mon 09, 2018 2:02 pm 
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Harry,

I suspect candle wax would be fine if you feel the need to "lock" the slug in place. I have used bee's wax left over from jelly canning in the past and it worked fine.

If using an additional slug or piece of brass to adjust the inductance with the current stuck slug isn't workable then before pulling the coil I would remove the remains of the old slug and try a new slug. A precision screwdriver with its blade applied to the slug and tapped lightly in a couple of places should fracture the slug and let it come out. Flush the remaining parts out of the threads using compressed air and a tiny brush or pipe stem cleaner then try your new slugs to see if one will work. You can try a little a VERY light coating of light grease on the threads of the new slug if it is trying to stick. Don't over-think the adjustment because the slug setting doesn't have to be perfect but just needs to be adjusted slightly down from peak on the side that causes oscillator output to drop slowly.

When trying to fracture the old slug don't hit it too hard and damage the coil and form. A fairly light tap is all that is needed to fracture the very brittle ferrite and then it should fall out in pieces.

And if you need help cracking the core you can send it to my daughter who has a lot of recent experience cracking open geodes after I took her on a geode hunt one day during her spring break. The cats and I have learned to watch for flying rock fragments :)

Rodger WQ9E


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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Apr Mon 09, 2018 5:04 pm 
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Harry,

I just used a scew-type slug on one of my homebrew oscillator coils and melted a small bit of paraffin into the phenolic tube. The slug screwed right in and has worked fine since.

Norm

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Apr Mon 09, 2018 9:47 pm 
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Something I've used in the past is a piece of flat, waxed cable/lacing cord, as a shim.

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 Post subject: Re: SX-117 Crystal Oscillator Slug Issue
PostPosted: Apr Mon 09, 2018 10:25 pm 
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Harry -
If you ever find someone with the 80 meter coil, I need the 20 meter one. Same exact problem you've described on one of my SX-117s, except the 20 meter coil.

Jeff
WB3JIH


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