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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Mon 22, 2018 3:22 pm 
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Chuck,

Thanks for posting the great photos of the transformer "innards". I haven't had an AGC related issue from the transformer caps in a SX-42/62 yet but I have had to replace a few caps because of either no or a broad shallow peak found during alignment.

I have too many projects now to create it but it would be very useful to have a site with measured gain levels for the IF strip and front end of popular vintage receivers along with AGC voltage developed with a given signal input so that restorers would have a point of comparison whether their project is performing as expected or if it still has issues. Some of the National manuals had this information as do some Sam's Photofact folders but it isn't available for most receivers. Measuring signal to noise ratio is a little complex but absolute gain would be a fairly easy measurement to make.

With the fading and no impact on the AGC you may have an issue post instead of pre-detection.

It looks like your SX-42 is going to be ready to go long before the azaleas begin to bloom :)

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Mon 22, 2018 4:14 pm 
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Rodger, such a site as you describe would be a very useful resource indeed.

And I know just the fellow with the receivers, test equipment, and knowledge to produce the site - and he's retired now too! Actually, this description probably fits a number of folks just here on ARF, let alone elsewhere.

Anyway, back to the world as it is, by post-detection do you mean audio? Or are you suspicious of the AVC still?

I'm pretty sure it's not audio because the signal just fades down into the noise. I didn't mention it, but I did run a brief test feeding audio in at the volume control and it seemed at the proper level.

As I recall (always suspect) also during my injection testing, I was able to get enough signal through to increase the AVC voltage by feeding it in at the mixer.

When I get back to it, hopefully today, I want to monitor voltages on the first three stages during fading. I will also likely try another 7F8 mixer/Osc.

As for the azaleas, we're planning a trip to Florida next month. Maybe theirs will be in bloom!

I'm planning on running over to check out Hamcation while we're there, but I'm trying to decide if I need the temptation of acquiring more projects that always besets me at such places. :roll:

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73, de Chuck K4CCW

"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Mon 22, 2018 5:19 pm 
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Chuck,

It seems like the AGC level should be varying if the problem is occurring prior to the AGC detector and if I understood your description correctly it is maintaining some steady AGC voltage reading during the fades. What happens to the AGC voltage when the antenna input is shorted?

There is a possibility that you have a fairly low level oscillation breaking out that is capturing the AGC and keeping it at a steady level rather than allowing the receiver gain to follow the carrier of the station being received. Checking the AGC level with no signal should show if that is the likely cause.

Enjoy Florida! A thunderstorm moved through at 3:00 A.M. and it is up to 55 today so it seems almost like Spring. I would take the Z06 out for a drive but the roads are a mess with leftover salt residue.

I would put together a good receiver database but my 14 year old daughter is keeping me rather busy :) The high school coach asked her to start practicing with his team even though she won't be eligible for high school play until next year so between two days of high school practice, two days of practice for her middle school team, actual games, and scholastic bowl crowded somewhere into the mix I have a pretty full schedule. I also was "volunteered" to be the photographer for the girl's high school team last week which works out since Anna wants to go to those games anyway. It is fun to watch her interacting so well with the older players and she is going to miss playing with them once the indoor league season ends and the regular season starts in a few weeks.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Wed 24, 2018 6:46 pm 
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I believe I’ve located the source of the fading problem and I’m almost certain it’s located the same place as several of the other “problems” that I have encountered – between my ears! :roll:

I returned to the shop yesterday morning only to find the fading issue was no longer there. After an hour or so of letting it warm up and checking out all the bands and seeing no evidence of a problem, I proceeded to touch up the alignment of both IF’s which went pretty smoothly.

I had to go through the discriminator alignment a couple times to get it to act like the procedure instructs. However, the end result sounds good to me and gives the full sound ’42 lovers always praise.

What about the fading you ask? Well, as I was winding things down for the day, I happened to lower the Sensitivity control to the “0” position for some reason. When I did I noticed that the sensitivity didn’t decrease immediately, but “faded” over the course of a second or two. :idea:

Intrigued, I played around with the setting of the control and found what seemed a threshold point at which the signal seemed (by ear) to disappear altogether.

You experienced guys are probably saying, “Well, yeah, what did you expect?” However, not being all that experienced, I proceeded to check out all the components in the area of the Sensitivity control and to familiarize myself with how it does its job by providing variable cathode bias on the two RF and 2nd IF stages.

All components checked in spec and the receiver operates normally as long as the control is above the threshold.

One issue I did notice is that C127 is spec’d at 25V, but during my testing above I saw the voltage at the control wiper to ground, which this cap is across, gets several volts above 25V when Sensitivity is set to “0”, which admittedly is not a normal setting. I’m going to replace this cap with a higher voltage one anyway.

For now, I’m going to attribute the “fading” to my having fooled and confused myself during the previous session.

I also wanted to mention a cautionary warning that the ANL switch is “ON” in the down position. If, like me, you notice periodically distorted audio, check to be sure the ANL is indeed in the UP (off) position.

Being a slow learner, I discovered this only after troubleshooting audio distortion and seeing a good symmetrical sine wave out of the detector, but at the top of the volume control a sine wave with the negative half showing noticeable clipping.

Having read a comment recently by either Rodger or Norm somewhere (maybe even earlier in this thread) about how certain ANL circuits can give distorted audio, I flipped the ANL switch UP just to see what would happen.

At his point I thought I was turning the ANL on when I flipped the switch UP. I’d had it on instead of off all of this time.

Hopefully all of you are quicker on the draw and don’t need to learn your lessons the hard way like some of us (I won’t mention any names).

What an education is an SX-42!

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73, de Chuck K4CCW

"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Wed 24, 2018 7:16 pm 
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Chuck,

It sounds like you are nearly there.

If you set the sensitivity too low when the signal is strong then once the signal goes into a fade the AGC can't compensate for it. The sensitivity control adds cathode bias and the AGC provides grid bias and if there is too much cathode bias the AGC cannot reduce the grid bias enough to overcome it.

About the only time you will need to reduce the RF gain control is when you are receiving SSB/CW signals and then it is like most traditional receivers where you need to advance the audio gain quite a bit and then use the RF gain to set the desired audio level; this ensures the BFO injection to signal level ratio is adequate for good demodulation. For normal AM operation just leave it at max. It can be used to some benefit on the lower bands to reduce gain where the band noise is less obnoxious but for most of my gear the RF gain control stays at max most of the time.

Changing the capacitor isn't a bad idea but at least if that one fails short the only damage will be the RF gain will be stuck at maximum. On a related note this is where tube substitutions can go bad because the RF gain and AGC circuits were designed for the original tubes and if tubes with different characteristics, particularly in terms of their response to small changes in bias, are used then the circuit will not work at all as intended. I once tested a "mint condition" SX-62 for a local and the gain went from full to nothing in 3 increments of the sensitivity control. I first suspected a control issue but the culprit was some "Mr. Modifier" changed the front end and some of the IF tubes to make it hotter and in the process destroyed the gain control characteristics of the set.

The discriminator drifts quite a bit in the first 10-15 minutes so let it warm up that long before aligning it and then expect somewhat reduced performance during the first few minutes of usage after every power up. Unlike later FM detectors the discriminator type will provide demodulation of FM at three points for every station with only the center point being correct; off to either side it will "slope" detect like a regular AM detector. For strong signals the tuning meter can guide you but if you aren't used to this type of detector the easiest method is to first set it for AM mode and tune for maximum distortion (which should also be the peak reading on the signal strength meter) and then change to FM mode. Tuning for maximum distortion on AM centers the signal in the passband which is where it should be for proper FM operation.

Hallicrafters tried to make a number of their receivers easier to use for the non-radio types and part of this was the color coded dots used for normal control settings along with having the toggle switches straight up for normal broadcast operation. My SX-88 is basically the same way except the three position toggle on the left is put in the center position (it selects CW in the up position, AM in the center, and SSB in the down position; the SSB position uses a BFO amplifier to increase injection). Think of it as an early form of human device engineering and Hallicrafters mostly did a pretty good job of making their receivers fairly intuitive to use.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Sat 27, 2018 11:58 pm 
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Eureka!!

A whole day of good behavior out of the SX-42, and my synapses.

All systems behaved properly during RF alignment (I lost count of how many times this was done on this project, but, then, I surely needed the re-training).

I will finish the physical cleanup of the exterior and show you her shining face once that's done.

My thoughts for now are to leave further cleaning of the top of the chassis for now, as I'm way past ready to move on to a new project. That part of the refurb may have to be left for the next caretaker, as my interests lie more on the circuitry side of things.

Many, many thanks to all who have helped to get me this far with this project.

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73, de Chuck K4CCW

"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Sun 28, 2018 4:05 am 
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Congratulations, Chuck! I know exactly how you feel. While I have not been working on my SX-62 as long as you have, I have had it on the bench since Thanksgiving. It’s starting to leave an impression in the bench top but my upper body strength is getting better from moving it around on the bench. Lol! I have to thank both you and Rodger for coaching me along.

I much prefer the electrical work to the clean up and finish work. I am looking for a local place to get the steel case powder coated. It should look great sitting on the shelf. Not just to look at either. This will be a daily driver, for me.

I did open up my T25, 2nd IF, just to see if I would see any of the issues you were seeing. In my case, the two resistors were found to be spot on and the same was found with the 5 mica caps, with no leakage detected on my Fluke 289. I think I am going to let it play on the bench for a while, thinking my occasional distortions on strong signals may be a tube issue. I now have some spares to throw into it, which has given some positive results, so far.

Thanks for allowing me to tag into your post, and I am looking forward to seeing how your 42 looks.

Best of luck.

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Chris
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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Sun 28, 2018 4:28 am 
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Good job, Chuck! You inspired me to tackle another of these 42's. I have one in the garage in pretty deplorable shape that will come out to the bench in a week or so. I am eager to investigate some of the areas you found worth checking and will use your thread as guidance.

Norm

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Wed 31, 2018 10:48 pm 
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Chris and Norm, thanks for your kind comments. It's good to know some have found this useful.

I was amazed to see the view counter fly past 10,000 yesterday. The only thing I could figure out was that I was the best alternative to the SOTU last night. :D

As promised, I wanted to post these pix of the outsides of the SX-42 in case some may find them useful or interesting. I didn't include any of the case itself, as it needs even more TLC than what you see here. I may follow Chris' lead once I see how his cabinet comes out for his SX-62.

By the time I was finished cleaning up the front panel and the knobs on mine, I was reminded by my hands of why I had to give up woodworking 3 years ago. Last night was the first time in a long time I had to take an Aleve!

Here's a couple views of the entire front as well as some close-ups of each half for greater detail.

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And here's one of the S-Meter. I wanted to give it special billing because I really like its looks and would love to find one like it to replaces the cheezy cheap one in my HBR-16.

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And to round out her final photo session, a couple top chassis views and a couple of the rear panel shots, showing the added fuse holder and slightly relocated line cord entrance. The fuse holder was installed in a slightly-enlarged hole originally used for the line cord entry.

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If I ever complete the job by redoing the cabinet - or, more likely, have it done - I will update this saga.

For now, as one of my favorite actors once said, "Here endeth the lesson."

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73, de Chuck K4CCW

"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Wed 31, 2018 11:05 pm 
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A very pretty receiver Chuck! If I had a nice spare cabinet I would send it to you because with all of the work that you have done that one deserves a nice case.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jan Wed 31, 2018 11:23 pm 
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Thanks Rodger, and thanks for all your support along the way.

I suspect once I've had a rest from it (by that I mean other projects for a change) I'll come back and get the chassis and case cleaned up as well. For now, I am enjoying the great sound while I work on other things for awhile.

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73, de Chuck K4CCW

"The question is not what you look at, but what you see." Thoreau


Last edited by WoodchuckTN on Apr Mon 30, 2018 1:47 pm, edited 1 time in total.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Feb Thu 01, 2018 12:53 am 
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That really looks beautiful, Chuck. I am including a few photos below to motivate you toward getting the case done. My local powder coater charges me $80 for a three color job like what I did for my 42. Two colors is usually $75. I always give him a tip because I appreciate his taking on these radio basket cases. I don't put a bit of effort into cleaning the thing before hand--just give him the rusty old mess with all the parts stripped off. They bead blast it and coat it. I get it back in a day or two. It is totally worth it to me, as I would much rather spend my time doing the fun stuff and I don't consider sanding and prep work fun.

If you decide to take it to a powder coater, bring along the cover to the transformer. As long as they are doing the black, they can make that look good too. If you choose another color than black, it would also go that color and compliment the case.

Norm


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Feb Thu 01, 2018 1:06 am 
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Motivation for sure, Norm. Thankfully mine is like a new one compared to your first pic, but it would sure be nice to have it look like your last pic.

Do you have any retained info on the colors and type of paint used? I have a new neighbor who seems to be doing a lot of auto body finishing in his big garage. I might approach him and see what his work looks like. If it's good enough, I'll see about having him do it.

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"The question is not what you look at, but what you see." Thoreau


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Feb Thu 01, 2018 1:25 am 
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I have had no great success with getting the colors to look like the original. I can't get custom colors as the price shoots up, so I go with what is in the color chart. Case is black even though the Hallicrafters black either fades to very dark gray or it is dark gray. I tried to have my guy use a very dark gray on the second 42, and it came out light gray--but I used it anyway (he got the wrong color). The lid is tricky. I used a silver with some gold in it for the one in the photos--that seemed pretty close and looks great. The second one I couldn't remember the color # and went with a grayer silver. My 62 I just did silver. Have the car guy paint it if he will give you a good price. It is the prep where all the work is. Painting is nothing, if you can avoid fish-eyes.

Norm


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Feb Thu 01, 2018 2:36 pm 
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Chuck, Rodger, Norm,

Chuck, all your efforts have paid off, whether you slide it back in the case or not. I think it looks great, and should sound as good or better than it looks with a good speaker. I have been using a speaker from an old cheap Zenith component stereo system that was sitting around the shop with my SX-62 and it sounds great, even on BC AM! I did find it interesting that you added the fuse holder on the back apron. My 62 had one mounted, from the factory, on the top of the chassis, near the power transformer. I wonder if it was added in a later build? I appreciate all the help and encouragement you have given me with my 62. It would not have been as much fun without it.

Your work here has inspired me further into getting me into starting on my 42. I think I am going to hold off for a while and tackle something different, and less intense for the next project. But am still on the fence. I still need to finish the case for the 62, though.

Norm, your 42 and 62 have inspired me to have the cases powder coated. They look great! I just need to find someone to either do both blast and powder coat. I am still looking. I have the 62 and a NC-173 to powder coat. The face of the 173 will be the biggest challenge. I am afraid of loosing the engraved lettering if the blaster gets too heavy handed, or uses the wrong media. Warpage of the flat panel top is also a concern. I am thinking soda blast is the answer, as the cases are in relatively good condition, with little rust, just needing paint removal. I do not know what kind of surface they need to get a good finish. I would like to have one guy do the whole operation. Like Chuck, I find the clean up and finishing less satisfying than the electronic work.

Rodger, as with Chuck, your council, encouragement, knowledge, and great stories have been priceless! I, for one, can not thank you enough. I look forward to your encouragement and deep well of knowledge in the future.

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Chris
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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Feb Thu 01, 2018 3:30 pm 
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Chuck has done a wonderful job of providing good documentation of this adventure in restoration and I am confident it will be used by a lot of future SX-42 and SX-62 owners.

Threads like this one make me think that the complaints over bringing "zombie threads" (those that were started a long time ago) back to life are wrong. Hopefully new material will be added to this thread in the future as Chuck (and other restorers) find additional bits of information applicable to restoration and operation of these fine post-war receivers. It is very nice to find a bunch of information in one thread on a forum instead of 30 different very similar threads on the same forum and that has really hit home with me this morning as I have sifted through numerous threads on high ISO image processing to put together the information I needed instead of spending a few minutes reading one or two good threads of information like you find in this one.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Apr Tue 03, 2018 8:04 pm 
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HI all -- well I had a great post written and my browser crashed trying to submit it. So I will try again to remember...

I think I have the right forum of Chuck's this time, versus the one I snagged before. He told me it would be OK to tack on.

A recap: Finally got the BFO working. The problem was a brand new component that was bad right out of the package. Once I replaced it, everything started working just fine again.

I've now completed replacement of all paper caps throughout, many of the silver micas that I've found bad, and all carbon comp resistors in the IF and audio sections. The radio works on all bands, even FM. However, I have a couple of problems left that I'm hoping someone might have some advice regarding. I'm trying to get the radio done so I can surprise my Dad with it before Dayton. He's also getting a rebuilt Ranger if I can ever get the SX-42 off the bench!

So here are the issues I have now:

1. Distortion on SSB/CW on bands one and two: Bands three and up seem to work well with the BFO. I can tune SSB signals without too much trouble, and I have good audio. AM is fantastic on all bands. However, when I go to bands one and two, I get pretty severe distortion and lose the BFO on really strong signals. I know the process on tuning SSB on boatanchors -- ride the sensitivity, BFO frequency and audio, but this isn't that. No matter what I do, I can't eliminate the distortion. I am not really sure where to look.

2. Sensitivity on bands one and two (likely related to above): On bands three and up, the sensitivity control works as expected - Ten max, Zero min. However, on bands one and two, turning sensitivity to zero doesn't kill the receiver gain much at all. It also doesn't help with the BFO distortion described above. I've traced the circuit, and I don't see why the sensitivity control should react differently based upon the band selection.

3. S- meter action is weak: Again -- likely related to the issues above. S-meter action is pretty weak. When AVC is on, I see a little meter deflection, but not really what I might expect on an AM signal that's booming through.

4. Broken ferrite in RF section coil: A former owner was a bit too persuasive in trying to get one of the band three coils to turn, and broke the top out of the ferrite core. It looks like it's still in one piece inside, but its days of being turned are over. I have a ferrite from the RF section of an SX-101, and it appears to be the same slug, and will screw into the coil forms. Would this be OK to use? How best to get the old one out without further damaging the coil form? Or should I leave it alone since the radio seems to hear OK?


So -- would appreciate any thoughts on the above issues!

Jeff
WB3JIH


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Apr Tue 03, 2018 8:37 pm 
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C25 is a prime suspect for your band 1 and 2 gain reduction issues. The first RF stage isn't used on this band so gain control of the second RF tube is a prime part of gain distribution for these bands and if C25 is leaky then gain control range for that band is reduced. Check resistance to ground at the cathode pin of the second RF stage with the gain control set at minimum. This is one of the front end caps that likes to hide.

It can also be a tube issue, make sure that a different tube type with different gain control characteristics hasn't been substituted.

For the S meter reading take a look at your AVC voltage and see how much is being developed on strong stations to determine whether there appears to be an overall gain issue or a metering circuit issue.

A couple of possibilities on the broken core; if the band it affects is working to your satisfaction the safest thing might be to leave it alone. To test how far the actual inductance is from desired try alternatively inserting a small brass screw or nut into the coil (attach it to a plastic alignment tool) and then do the same with a small bit of ferrite material (could be the hex core out of a more modern coil. If the insertion of either of these results in a drop in level no matter how shallow or deep they are inserted then the setting is optimal as is. If they make a change you will have to decide whether the change is enough to justify the risk of taking out the remains of the old core. If adding ferrite increased output level then you could try screwing your donor core in slightly with the old core still in place.

This is an awkward way of simulating what was done with a "magic wand" which was a standard part of old alignment tool sets. The wand has a brass slug in one end (reduces coil inductance) and a ferrite slug in the other (increases inductance) and provided a quick test of optimal setting. I was fortunate to find a big set of tools at a hamfest that came with one of these handy tools but it wouldn't be difficult to make your own.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Apr Tue 03, 2018 11:05 pm 
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Rodger -

Pin two on the 2nd RF 6AG5 shows 150 ohms with the sensitivity control wide open, about 10K with the control at minimum. I replaced this cap -- and it was a job...

Replaced the tube with another 6AG5 with no change.

I also checked the resistances on the first RF amp tube -- I got the same results.


I'm going to leave the ferrite alone for the time being.


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Apr Wed 04, 2018 12:21 am 
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Very odd, the only tubes on the RF gain control bus are the two RF stages and the first IF stage. Turning it to 10K should move these tubes to near cutoff.

Set the receiver to band 2 and measure the cathode voltage at the second RF tube as you vary the RF gain control and then do the same for the first IF stage. You will need the tubes in place as you do this so either use a test socket adapter if you have one or you will need to measure from beneath the chassis. It is a strange symptom with the effect from the gain control varying wildly for the first two bands compared to the other bands and the main difference is the first RF stage is not used for bands 1 and 2.

Rodger WQ9E


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