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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Wed 20, 2017 11:00 pm 
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Chuck,

Glad you found the hum problem. You are lucky the 7F8 tube came out OK because that loctal tube often wants to stick in place and access to it isn't great. One of the old timers on the coast when I first got my novice ticket nearly amputated a thumb when he broke a stubborn loctal trying to pull it out of the socket. When they are a real pain I try to tap the locator pin from below to coax it loose but that isn't possible with some equipment layouts.

My Grundig YB-400 portable shortwave receiver is one of my most used pieces of test gear. I would happily do without a tube tester before doing without an external receiver like this one. You can find many of the same problems using a scope but the external receiver approach is much simpler and requires no real setup work.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Thu 21, 2017 8:23 pm 
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Thanks, Rodger. As for the loctal warning, I saw it in one of your posts early in my return to the hobby a couple years ago and have been careful since then. I even made myself a removal tool from some appropriately-sized foam pipe insulation for tough or hot situations. The 7F8 in mine goes in and out freely though.

As for my other above-mentioned remaining issues, they have me wondering if I'm totally losing it. When I went back out this morning to begin tracking down the issues, all three issues appeared to be gone when I checked again in the process of a quick alignment check. :shock:

Possibly a tube or component burn-in issue? Possible further switch cleaning needed? We'll see. I plan to let it burn in while I try to get a handle on alignment of the xtal filter section. I have looked at every set of instructions (SAMS, Halli. for SX-42, and Halli. for SX-62) I know of and I just don't see what's being said.

I think maybe I just need to go mow some more lawn and try again in the morning.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Thu 21, 2017 10:36 pm 
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Chuck,

The alignment and use of single element crystal filters is probably the most poorly written and confusing parts of most manuals and with many of the Hallicrafters sets you also get the pleasure of setting it up for multiple bandwidths. The good news is it isn't too difficult.

I would start by disassembling the crystal holder and cleaning the element and contact plates because generally by now that is needed. If you align the filter without doing this step you may find yourself redoing the entire alignment. Most of the early HRO manuals have the instructions for this, basically use good concentrated alcohol to clean the crystal and its pressure plates and wipe dry with a clean cloth or paper towel before assembly. Do NOT touch the element of contact surface of the plates with your bare fingers after cleaning. Many of these holders have a ceramic or porcelain "gasket" between the halves which will crack if the screws/nuts are over tightened. It can be repaired with standard "super glue" but if you do this let it dry for a day before reassembly to ensure that fumes from the curing adhesive don't contaminate the crystal.

You can use a signal generator and scope to check the crystal before and after cleaning. Connect the signal generator output lead to one of the crystal leads and the scope vertical input to the other. Connect signal generator and scope grounds together. Set the generator for fairly high unmodulated output and slowly rock it around the crystal frequency and note the frequency and output level which will show a sharp peak at the resonant frequency.

In the non-crystal position align the receiver IF to either the frequency measured during the test of the crystal (preferable) or 455 Khz. You then adjust the IF transformer feeding the crystal filter (T24 455 Khz. secondary) along with the phasing control and narrow and medium selectivity trimmers to achieve the desired response. I believe that the instructions for the very similar SX-62 series (like the SX-62A) are easier to follow than the Sam's instructions-just keep in mind that the phasing capacitor in the SX-42 is a front panel control rather than the set and forget chassis setting of the 62 series siblings.

When the instructions call for "rocking" the signal generator it just means you are tuning very carefully around the IF point to find the desired peak or null and what complicates this is the IF transformer secondary feeding the crystal element forms a circuit so that both the frequency of the signal AND the tuning of the transformer affect this point so it requires a little back and forth adjustment of the signal generator frequency and IF transformer inductance to hit the perfect spot. Once you do this setting up the phasing notch along with narrow and medium filter bandwidths is simple.

Be sure to give the receiver and your test gear at least 15 minutes to warm up and stabilize.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Fri 22, 2017 2:48 pm 
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Rodger, thanks for taking the time to elaborate on the crystal filter issues. I have read and re-read the instructions mentioned above as well as a number of articles but my cranium is obviously both thick and somewhat leaky it seems. :D Your explanation does help, as always. Even better would be for you to jump in that pretty blue Corvette and make a visit to the Music City!

I will take your advice and measure, clean, and re-measure the filter before proceeding to have another stab at alignment of that area. I'm sure glad the filter is one of the more accessible components in the rig.

Yesterday a new problem surfaced during work on bands 4 and 5. The oscillator trimmers C43 and C45 appear broken. By that I mean the metal part where you insert the alignment tool turns freely, but I believe it should be turning the ceramic disc below it as well. Perhaps the metal has just become disconnected from the part it should be turning. I'm not sure how these are constructed so I'll be removing them for further inspection.

I'm certainly growing in empathy for folks like our friend Aidan who have tackled the SX-42. Restoring it is like trying to nail jelly to a tree!

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Fri 22, 2017 4:42 pm 
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Before I get back to mowing again, I wanted to post these pictures of C43, the oscillator trimmer for band 3. C45 is in similar condition with not quite as much of what I believe was a coating that made up the "stator" of this trimmer rubbed or fallen off. I may be talking through my hat, as I'm not familiar with the construction of these particular caps. Hopefully the experts here can enlighten me.

C42 has what looks like a dark circular coating beneath the rotating part of the trimmer and seems to function ok.

Your thoughts appreciated.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Fri 22, 2017 4:53 pm 
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Chuck,

That coating is just residue from the rotor plate and any cleaner, lubricant, corrosion, debris, etc. that was deposited on the ceramic. At worst it needs to be cleaned off if it becomes sufficiently conductive because it will reduce the minimum capacitance.

These capacitors are made in two styles. In one the stator is located within the ceramic material but others have it mounted on the bottom and that may be the case with yours if it isn't working because it means the stator plate has come loose and fallen off. Try to look at one of the properly working same style trimmers to see whether it has the external stator plate, it would be mounted to the recess in the bottom of the capacitor.

On edit: An external stator would have the same half moon shape as the rotor and would live in the half moon recess in the bottom.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Sep Fri 22, 2017 5:25 pm 
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Thanks Rodger. This one must have the internal stator and maybe just needs cleaning, as it measures right on the money and ajusts properly from 2 to 6 pf.

Hopefully when I clean and reinstall it, the mysterious radio fairy will have visited the radio once again and resolved the problem.

It might just be what an old friend of mine used to call, "Malfunction between the headsets."

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Oct Tue 31, 2017 4:51 pm 
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I know I owe the followers of this saga (both of you :D) several updates, but first I need to ask a quick question.

Regarding the IF crystal filter, how much change should typically be expected between its frequency before and after cleaning?
In my case:

Before: 456.6 khz

After: 458.000 khz

Does this fall within the normal range in your experience?

I don't want to go to the trouble of installing it and aligning to it if this is too much variance.

Thanks for your input.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Oct Tue 31, 2017 5:08 pm 
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Chuck,

I assume you mean you opened the crystal holder and cleaned it? How are you determining the frequency of the crystal? The critical thing is whether it works in the radio. I would re-install it and try it. You would adjust the frequency of the IF to match the crystal.

Norm

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Oct Tue 31, 2017 5:12 pm 
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Chuck,

I would let it go a couple of days and measure the crystal again and if it stays at the same frequency it should be fine. You will find that you can fine tune the frequency by changing the tension on the case screws so that is probably largely responsible for the difference you are seeing now.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Oct Tue 31, 2017 5:20 pm 
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Thanks Norm and Rodger. Always valuable advice.

Norm, I am using the simple method given earlier by Rodger - TEK 453 scope on one side, HP-606B on the other, monitored by an HP freq counter for good measure.

I like the idea of "aging" the xtal for a bit.

Always plenty of other distractions to attend to while waiting. Maybe this is a good time to do the updates to this thread that are overdue. :roll:

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Oct Tue 31, 2017 8:45 pm 
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Chuck,

I was measuring crystals using the HP 410B RF voltmeter connected as Rodger described-with the crystal in series between the generator and the voltmeter. I was getting high readings for the frequencies of the crystals. Peter Bertini suggested the measuring configuration may be affecting the result and to try another method with the crystal across the generator output. Here is the post:

"Thanks, Pete.

So that is a cool experiment. I connected the high side of the generator to the RF voltmeter probe with two--in series--33p caps. At the junction of the two caps, I connected one side of the crystal. The other side went to the generator and voltmeter grounds--which are connected together. I get a voltage spike for the crystal-- but this time, low of the frequency and much, much closer than the earlier configuration.

Again, I am not sure exactly what this tells me about the crystal accuracy, however, it does tell me the crystal is functioning close to its value. The radio has adjustments for correcting frequency discrepancy between bands and some is expected.

Norm."

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Wed 01, 2017 1:17 am 
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And to add to the good advice provided by Norm keep in mind that the exact frequency of the crystal used for these single element filters isn't very critical EXCEPT for a very few oddball later receivers that use a single crystal element filter for CW in conjunction with a crystal lattice or mechanical SSB filter (provides better skirt selectivity than the crystal by itself). The Yaesu FR-100 receiver uses this single crystal plus SSB lattice filter for CW and the Hallicrafters SR-400 transceiver does the same thing but at 1650 Khz. But for most vintage receivers as long as the crystal is within +/- 5 Khz. it will work fine.

The major concerns are that after cleaning the crystal provides a proper sharp reasonable amplitude response and that the frequency doesn't shift. I always do a before/after check of the crystal to gauge the response magnitude before and after cleaning and it is also good to have a known good comparison crystal if you have any doubt. The frequency peak may be different after cleaning and there is nothing wrong with that, it probably will also have a sharper response since the "crud" that was on the crystal is now gone.

Like Chuck found with his crystal the little ceramic "gasket" between the case halves is often cracked or damaged and if this material expands/contracts with temperature change it will also change the pressure from the crystal contact plates resulting in frequency shift. If you leave the crystal connected to the test setup while tightening the case hardware you will see the frequency shift as fastener tension is increased.

For band hetrodyne crystals, intermediate conversion oscillators, and carrier/BFO crystals exact frequency is much more important and any test setup should try to approximate the circuit capacitance of the actual circuit.

Keep in mind that the FT-241 2 and 3 digit "channel" crystals can be a good source for missing/bad single element crystal filters. Channels 46 and 327 are right on 455 khz and adjacent channels are close enough to work also. Another potential source are some of the older junked CB sets that used carrier/BFO crystals in the 455 Khz. range.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Wed 01, 2017 6:23 pm 
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Chuck, make that 3 of us that are watching, with great interest, I might add. :P
I just have nothing to add to the conversation, just sand bagging, and reading what the experts have to say. :lol:

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Wed 01, 2017 11:04 pm 
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Norm, Rodger, Chris, a sincere thanks for your posts. For me, on a challenging project like this, both the help provided by the "experts", as well as the encouragement provided by onlookers are invaluable in keeping me motivated to the finish line. Without such, I'm afraid I would have thrown in the towel much earlier.

I had hoped to get back into the shop today to at least check on the aging of the xtal filter and to post some pictures of the xtal cleaning process, but other duties took longer than expected.

Edit: For pictures of the xtal cleaning see entry at 12/2/17.

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Last edited by WoodchuckTN on Dec Sat 02, 2017 11:07 pm, edited 1 time in total.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Thu 02, 2017 3:13 am 
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I just learned I can subscribe to this thread so count me as a follower and learner. :D

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Thu 09, 2017 11:45 pm 
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OK, time to update all my loyal readers – all three of you:

Dropping back to the issues with the HF oscillator trimmers C45 (band 2), C43 (band 3), and C42 (band 4), I had good luck just cleaning the latter two with 91% Isopropyl alcohol.

C45 turned out to have a crack in the ceramic that ran all the way across the cap. That meant replacement was required. Having none in my stash that would allow mounting using the original bracket, I created a bracket for what I had using a modified small phenolic terminal strip whose mounting tab served as a grounding point just like the original.

I am not impressed with their mounting method for these caps, as it seems to put undue strain on the body of the cap, and then they are subject to break after only 70 years!

I’m not impressed with my method either, but it works:

Attachment:
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BTW, both C43 and C45 are part number 44A077 and nominally 2-6 pf adjustment range. The observant among you will note a small cap in parallel with my replacement kludge in the above photo, necessary to give the range of adjustment needed to put the oscillator high-end calibration where it needed to be.

As I bring this part of the update to a close, I have a question: :?:

As I went through a quick alignment of the RF stages for bands 2, 3, and 4 just to check for glaring problems before proceeding, I noted that several of the trimmers needed to be at max capacity (assuming this is fully compressed) and still headed for a peak when I stopped, fearing damage if I tightened them further. (After all, 50 ft.-lbs. is a lot of torque! Just kidding.)

Soon to follow: Crystal Filter Adventures

Edit: For pictures of the xtal cleaning see entry at 12/2/17.

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Last edited by WoodchuckTN on Dec Sat 02, 2017 11:07 pm, edited 1 time in total.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Fri 10, 2017 12:39 am 
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Chuck,

With the trimmers being at full compression before a peak you should check the indexing between the main tuning cap and the dial because it may be off. The main tuning cap should be fully meshed when the pointer is lined up with the last reference point on the low frequency end of the dial.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Fri 10, 2017 1:24 am 
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Hi Rodger, I'll check that in the morning - actually afternoon, as I go to have a skin cancer removed in the morning. Thankfully it's only a small basal-cell.

Perhaps you or someone can clear up a related question.

In the process of discovering the above business with the trimmers I got to wondering if the HF oscillator was operating on the correct side. That set me to researching which side the injection should be on for this receiver. None of my documentation answers the question, but I did find a post that indicated the injection is high-side for all but band 4. However, the poster didn't seem to trust his sources. He did find that setting the HFO accordingly got his SX working properly however.

In case I've buried the question, is there a way to tell whether injection should be high or low-side without documentation?

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Nov Fri 10, 2017 3:34 am 
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Chuck,

See: http://bama.edebris.com/download/hallic ... o%2021.pdf

It apparently started in their service update 13 and is referenced and explained in service hint 21 available at the above edebris link.

In general high side injection is used for pretty much every receiver on the lower bands but in some cases the highest band will use low side injection. If the manual doesn't specify the best approach is to try both high and low side and see which provides the best agreement between actual and indicated frequency across the band AND also check tracking at multiple points.

In some cases tracking side was chosen to provide a lower likelihood of image response in a certain segment but with the changes in shortwave frequency occupancy this isn't really much of a concern anymore.

I hope things go smoothly and painlessly for you in the morning!

Rodger WQ9E


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