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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Wed 07, 2017 5:40 pm 
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Great tip on the cuticle scissors! I will grab a pair next time I am out.

I had to use the same bent wire tip when restoring my Pierson KP-81 to unsolder enough leads to separate the two case halves of the front end. I think everything was wired up and then the manufacturer riveted the sockets and terminal strips in place.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Fri 09, 2017 11:52 pm 
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Well, as of 4:30 this afternoon all caps replaced except the two cathode bypass caps for the two rf amp tubes. :D

After spending about another half an hour or so looking at those two caps - at least what I could see of them - from every available angle, I decided to knock off for the day and tackle them in the morning when I'm fresh.

So far the best plan seems to be what several have suggested: cut the grounded end at the body of the capacitor and then carefully twist the cap back and forth until the other end breaks off at the cap body. I hope I can get my small forceps in to hold the far end lead as I twist so that the lead doesn't break off at the tube pin or damage the tube socket. If it did that I'd have to cry.

Also, it turns out that the 89D257-G schematic matches my receiver perfectly. I can't imagine doing this without an accurate schematic, as it's challenging enough figuring out where you are WITH the right schematic. Some of this challenge comes as a result of wanting to label things as I go along for later possible troubleshooting needs.

Doing things this way, for me, creates a greater knowledge of the circuitry and is much more than just shotgun replacement of components.

If things go well in the morning, tomorrow may be power-up day! After that, I know I still have to work on the tuning caps and mechanism, as the bandspread won't move the cap.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Mon 12, 2017 5:37 pm 
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As my grandchildren sometimes like to say, "Silly Papa!" If any of you folks with SX-42 experience read my last post, you were probably thinking something like that as well.

I spent most of the next day removing 4 capacitors, after an hour or so of reconciling my daily notes of components removed or checked. Checking against the parts list in the November 1947 94X242 Service bulletin, I discovered there were two more paper caps buried under the RF amps besides C11 and C25 which I had earlier identified.

The two I hadn't noticed before looked like large mica caps as you'll see below in the Nastiest Caps photo. These are C12 and C26 in the schematic.

Attachment:
Nasty Caps.jpg
Nasty Caps.jpg [ 83.95 KiB | Viewed 2422 times ]


Here's a shout of the location of these four caps.

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RF Cap Location.jpg
RF Cap Location.jpg [ 167.09 KiB | Viewed 2422 times ]



Somewhere in all this identifying of components I made a happy discovery: one can gain some access to the inside leads of C11 and C25 from the top of the chassis. Using this new access, I was able to actually cut the inside leads fairly close to the cap rather than the twisting earlier planned that might have brought collateral damage to the tightly-packed area.

Still having the SX-42 lashed into the Steve Strong chassis stand, I was able to remove three of the 4 "Nasty" caps - all but C25. For this one, the end gusset or panel of the chassis had to come off, and for that the receiver had to come out of the chassis stand. :(

As often is the case (for me) the dread of doing was worse than the doing, especially as my youngest grandson was available to lift one end of things in the process.

As you can see in the picture below, there is much greater access to the bowels of the RF deck with the end panel/gusset removed. Given this better access, I was fairly easily able to check most of the critical resistors in that area and found several warranting replacement.

Attachment:
End Gusset Off.jpg
End Gusset Off.jpg [ 178.32 KiB | Viewed 2422 times ]



That and installing the four "Nasty Cap" replacements is today's project. I wanted to give you this update in case I don't survive, as putting the cap's back in looks to be at least as challenging as safely getting them out. I'll be implementing some of the creative suggestions for "custom" soldering guns/irons given here.

As I think Wilford Brimly used to say, "Thank you for your support."

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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: Jun Mon 12, 2017 8:09 pm 
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Chuck,

I ended up removing the metal brackets with the trimmers attached to get at C11 and C25. It made it easier. For the first SX 42, I did not remove these trimmers and it was rather a PIT, and I was worried I might have a short where I couldn't see the entire lead.

Norm

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Mon 12, 2017 9:37 pm 
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Thanks Norm. When C25 would not come out the side past that bracket the other day, I had tried what you suggest but the bracket was too restricted by its heavy connecting leads. The only way I could get the caps out, once cut free of their leads, was to take them out past their respective RF coils towards the center of the chassis. C25 even then could only be gotten out by clipping one end of R8 and R11 to allow it past them. Luckily both of these resistors were significantly out of tolerance and needed to be replaced anyway and I hadn't done that yet.

********** BULLETIN - BULLETIN *******

As of 1445 CDST according to the official log, the four "NASTY CAPS" have been safely replaced!! :D :D :D

Here's a shot of them resting comfortably in their new surroundings:

Attachment:
2017-06-12 13.51.06.jpg
2017-06-12 13.51.06.jpg [ 69.49 KiB | Viewed 2409 times ]


Now, just a few more resistors, a new line cord and fuse holder, testing the tubes, and I hope to be easing power to it later this week. For now, the next couple days will be devoted to a short trip for my honey's 70th birthday.

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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: Jun Wed 21, 2017 5:07 pm 
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Time for an update.

“Replacing few more resistors” of course took several hours since they were mostly in the bowels of the RF section with tentacles firmly wrapped around the infamous bandswitch – not to mention the challenge added by my chronic OLD flaring up. :D

I might note that virtually all of the 15 ohm resistors in the RF section were found to be at least 100% out of tolerance. I’m not sure this would be a big deal operationally (Rodger and others can tell us), but as they were not as inaccessible as the RF bypass caps I went ahead and replaced them.

Once all the resistors and caps were finished, I installed a new 3-wire line cord and fuse holder, followed by testing the tubes and cleaning the pins/sockets in the process.

Finally yesterday I powered it up! My daughter, my grandchildren, and a family visiting them came over to witness the event. My daughter made a big deal of it because she lives next door and has witnessed the life-changing effect this receiver has had on me in the 2 years I’ve had it and have been preparing for this moment.

Luckily, there was no smoke and, once I switched from Standby to Receive :oops: , the B+ and regulated B+ were almost spot-on at 253V and 153V respectively.

There was a round of applause as I tuned across the broadcast band and beautiful, clear audio was heard by all! Yours truly was almost in tears and probably would have been had there not been such a crowd watching, especially as my youngest (12) grandson was quite impressed.

Brief checks after the crowd dispersed showed that it passed signals on the lower 4 bands right off the bat with varying sensitivity, but the upper two bands appear deaf - unless I was doing something wrong with my setup in my haste.

These two upper bands use the 10.7mhz IF so perhaps there's an issue there.

Another symptom is that the B+ and reg. B+ drop by a few volts when either of these upper two bands is selected so something could be shorting in the band switch. (Remembering Aidan’s problem in this regard, Rodger)

Not sure if lawn chores will permit more troubleshooting today, but my plan is to find the source of the B+ loading on those upper 2 bands before anything else.

Thanks for reading.

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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: Jun Wed 21, 2017 5:26 pm 
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Chuck,

Congratulations on getting your SX-42 working!

I expect those small resistors are the "squeal stoppers" in series with the RF amplifier tube control grids; if so then somewhat increased resistance won't make much difference but when resistors go way up in value (as in 100% or more) then they could easily have been on the way to complete failure so replacing them was a good thing.

I wouldn't be surprised with the current demand being slightly different on the high range but I am surprised the regulated voltage dropped. Is the VR tube still glowing reasonably brightly? It may be near end of life and if so then the regulation won't be too great on any of the ranges.

I would first make sure the HFO is operating on the upper ranges and then start going through the IF to see if it is passing a 10.7 Mhz. signal. Are both AM and FM dead on the upper ranges?

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Wed 21, 2017 5:44 pm 
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Hi Rodger, I was hoping you'd be able to respond. Thanks for the suggestions and questions.

I'll check into the things you asked about, but am pretty sure I checked both am/cw as well as FM when I was doing the quick testing yesterday. In all the excitement of having ANY of the bands working right away, I may have fat-fingered something (you know, like the Standby/Receive switch :oops: ).

I did do some resistance checks on the 7F8 and the IF tubes, switching between bands 4 and 5 to see if anything popped out at me but all seemed in order.

I'll do the osc operational test as part of the next steps. I have a DX-400 and a Drake-made "People's Radio" that come in handy for that.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Thu 22, 2017 1:39 am 
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OK - you shamed me in to it. Went to the storage unit and picked up the 42 that's been waiting. Keep up the commentary and post more pictures.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Thu 22, 2017 2:04 am 
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Shanghai Jack wrote:
OK - you shamed me in to it. Went to the storage unit and picked up the 42 that's been waiting. Keep up the commentary and post more pictures.


Chuck,
You have started a movement to free many innocent SX-42 receivers from their basement and storage dungeons. Think of yourself as the founder of the Innocence Project for neglected Hallicrafters receivers :)

Very well done!

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Thu 22, 2017 3:10 am 
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rsingl wrote:
Shanghai Jack wrote:
OK - you shamed me in to it. Went to the storage unit and picked up the 42 that's been waiting. Keep up the commentary and post more pictures.


Chuck,
You have started a movement to free many innocent SX-42 receivers from their basement and storage dungeons. Think of yourself as the founder of the Innocence Project for neglected Hallicrafters receivers :)

Very well done!

Rodger WQ9E


Gentlemen, I'll be glad if my efforts inspire and maybe help some others as the postings of many others here on ARF have done for me. It would be great if at least a little of that can be repaid.

Jack, this would be a good time to start yours while I still have my chassis opened up and while things are still fresh in my mind. At almost 73, I can't count on the latter phenomenon very long :lol: I'm always happy to answer any questions from anyone.

As for the inspiration part, any of you younger fellow's should just think, "Well, if that old codger can do it, I should be able to as well."

Rodger, I took a little closer look at the schematic and saw that the 7H7 limiter/IF only gets B+ for its plate and screen when the upper two bands are selected. As you indicated, that might explain the greater plate load (voltage drop) I saw yesterday.

Whereas I was a good boy and got the lawn chores taken care of today before the remains of Cindi hit us in the next couple of days, I hope to spend the rainy days looking deeper into the above issues and will report back.

Thanks for keeping me company on this interesting journey.

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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: Jun Sat 24, 2017 12:20 am 
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After taking advantage of the brief period without rain this morning to sweep up the grass from Wednesday's mowing, I had a little time to look deeper into the issue of the top two bands being deaf.

Well, I must confess to probable "malfunction between the headsets" as we used to say. Either that or the fact that I didn't slow down long enough to clean the switches, including the all-important bandswitch, between re-capping and powering it up came back to bite me. I knew this needed to be done but was in a hurry to see how much life had returned to this old beauty.

I'm happy to report that she passes a signal on all 6 bands and even passes FM - at least from my 8656B, not off-air.

Starting with the bandswitch, my next task is to thoroughly clean the switches with carefully-applied DeOxit on the contacts, NOT the phenolic.

I might mention I successfully restored a completely nonfunctional toggle switch (AVC I think) using Pix's (I believe) WD-40 method. These old switches don't have much access to the innards, but the WD-40 gets in there and, after a few flicks of the switch gets it going again. It's still working well after several weeks now.

BTW, if anyone happens to have a parts unit I'll need a side cover for the RF section one of these days if you have one you can turn loose of. I'll do a formal WTB post at some point.

Stay tuned and thanks for reading.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Sat 24, 2017 2:43 am 
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Good job Chuck! With a good speaker the SX-42 sounds very nice on the FM BCB.

See if someone who has a SX-62 open can measure the cover because I am pretty sure they are the same and there are a lot more SX-62 receivers out there as parts sources.

Rodger WQ9E


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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Mon 26, 2017 1:22 am 
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Nothing like spending a glorious Sunday afternoon (sunny, 80deg., no humidity to speak of) cleaning the dozens of contacts on both sides of all 11 wafers of the bandswitch (SW-1), 2 each on the Selectivity(SW-2) and Reception(SW-3) switches, and 1 on the Tone switch (SW-4). However, I wanted to get them done so they could have time to dry out before I apply power again tomorrow some time.

I thought the Reception switch had lost a ball bearing, but upon closer inspection I could see it never had one. Rather it uses a pressure-tab detent type and the tab, like me, is showing its 70+ years and is apparently pretty weak, as there is barely a detent effect. If it is too annoying, I'll look for a replacement, but it would almost have to be from a parts donor.

Tomorrows task will be to work on getting the tuning mechanism working properly. Somewhere along the line I acquired a copy of a 4-page article specifically about how it comes apart, how it works, and how to deal with common problems. Many thanks to the one who wrote it and the one who gave it to me.

I already grabbed the low-hanging fruit and lubricated the bandspread cap yesterday to eliminate it as the cause of binding. I loosened the coupler at the end away from the cap to allow the cap to rotate freely during the process. Now if I can just remember to tighten the screws once I'm done with the mechanism. :roll:

I think I'll put a post-it note on it right now.

Thanks for reading.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Mon 26, 2017 2:05 am 
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The main tuning is quite a confabulation and doesn't age well--at least on the two receivers I have. I admire Hallicrafters thinking when they designed the stop mechanism--but they should have factored in years of corrosion, muck, and very small ridges that wear down. I had to do some creative bending (slight), shimming, and adjusting, to get my receivers working properly. A small brass brush was very helpful. The face was on an off a few times and at one point the whole mechanism was extracted from the radio. This of course screws up the alignment.

The key thing for me was starting the alignment procedure with the main and bandspread tuning capacitors in the right place in relation to the dial. For the BC band, there are no inductance adjustments for the antenna and RF coils. Plus, the trimmers cover a very small range just 2 to 6 pF--that is 4 pF. Having the adjustment range work for all the bands for all the trimmers--means getting the main tuning cap in the sweet spot--which--after all the years may not be exactly as described in the manual. Then the bandspread needs to be in the right spot as well.

Sounds like things are going fine, Chuck. Keep at it.

Norm

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Mon 26, 2017 2:38 am 
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Thanks for both the advice and the encouragement, Norm. I'll keep the info about the "sweet spot" in mind when I get there and may need to pick your brain some more then. Right now I have mechanical issues with the mechanism and possibly a binding main tuning cap that has my full attention - assuming the switch cleaning I did today did not generate other "challenges".

I don't like to always refer to these things as problems because this is a hobby after all. :D

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Tue 27, 2017 8:32 pm 
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Time to call for help.

I was in the process of doing a quick alignment of the IFs to eliminate at least a little of the "deafness" so I could more easily track progress as I work on some of the mechanical issues. At least that's what I told myself to justify jumping a little ahead. :D

Well, along the way after the 455khz alignment went well, I wanted to see how well a signal fed into the antenna would do on the broadcast band now that the IF tune-up seemed to have really been needed.

No joy.

Lots of sensitivity with just a clip lead on pin 1 of the 7F8 mixer/osc. Nothing even with outside long wire OR signal generator into the A1 antenna terminal with A2 jumpered to ground via A3.

A little tracing revealed that the antenna coil, T5, primary was open. The good news is that I could see (with magnifying headset) the tiny lead dangling near terminal D of T5 and it looked like all I had to do was reconnect it. The bad news is that it turned out to be the terminal end, not the winding end. :( :(

I'm back here to ask if anyone knows how to access the winding on these RF transformers? Each bank is mounted to a metal strip at the chassis that is in turn riveted to the chassis.

I hope there's something I'm overlooking, as I don't see a way to fix this winding without removing the transformer.

Color me stymied.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Tue 27, 2017 9:16 pm 
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I would suggest you remove the transformer, carefully unwind the turns of the primary--counting them as you go, and then rewind with new magnet wire of the same approximate gauge. The exact number of turn is probably not critical as that side is not tuned. I don't remember if the primary is the upper or lower coil on the form --or if it is wound on top of or underneath the secondary. You may need to re-wind both.

An alternate route would be to abandon T5--create a new T5 and add it in where you have the space running leads to the existing connection locations. My BC band on the SX 42 I am doing now has very low sensitivity. It doesn't use the first RF amp stage. I have been struggling with it for some time. I am about ready to abandon the first two transformers, wind my own and create my own tuned circuits for that part of the chain. If I didn't have another SX 42 that works fine, I would say it is just bad design.

Norm

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Tue 27, 2017 9:27 pm 
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Hi Norm,
I'm familiar with the procedure you outline, once I have the transformer in my hot little hands.

It's the HOW of removing it that I can't figure out so far.

One thought I did have is that I could just forget about the broadcast band, since that's all T5 serves.

If anyone has copies of the band-by-band schematics, I could sure use them for the first three bands. Somewhere along the line I acquired part of them, the top 3 bands, but not the lower three.

BTW, Norm, I'll keep your latter ideas in my back pocket as well. Thanks for weighing in.

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 Post subject: Re: SX-42 Begun - At Last!
PostPosted: Jun Tue 27, 2017 10:31 pm 
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When you look into the coil form from above, isn't there a screw that is threaded into the bar below, holding the form in place?

Norm

Image

Image

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