Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Sun 24, 2021 4:37 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 28 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 3:28 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
I have many radios like most people here: this one is a one owner great condition SX-17 (later model with the 6H6) I got from one of the developers of the Cray computer. So for a EE/Comp Sci guy its cool to own something owned by one of the key guys who developed a revolutionary computer system I studied as an undergrad.

The guy bought this new as a kid and used it then used it until about the 1970s and stored it in his house - he had the R-17 too but it got lost in a move.

This set had not been powered on since maybe 1978. Anyway I replace the wax crayon caps, tested the tubes and fired it up with a variac. It made a hum and then smoked a 1K resistor (on schematic). Not what I expected - I have repaired and worked on about 20 SX-28s in the last 90 days in all conditions and I did not expect a smoking resistor of unknown reason on such a nice condition set...

Attachment:
IMG-7191.JPG
IMG-7191.JPG [ 985.75 KiB | Viewed 500 times ]


Closeup of the smoker resistor (1K - R39 I believe):

Attachment:
Screen Shot 2021-09-16 at 9.25.54 PM.png
Screen Shot 2021-09-16 at 9.25.54 PM.png [ 860.26 KiB | Viewed 500 times ]


Last edited by mrrstrat on Sep Fri 17, 2021 3:50 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 3:30 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
Some pix of the "problem zone":

Attachment:
IMG-7195.jpg
IMG-7195.jpg [ 2.15 MiB | Viewed 498 times ]



Attachment:
IMG-7194.jpg
IMG-7194.jpg [ 2.62 MiB | Viewed 498 times ]


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 3:39 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
I burned a couple 1K's and after that just would twist a new one in long enough to try measure some voltages before it burns up. I have only the 5Z3 in it and the rectifier appears to be good and the 16uF/400s appear to be OK.

I could use a couple pix of a SX-17 as it looks like some features inside do not even match the original book schematic that came with it. It is obviously a "late" SX-17 as evidenced by the 6H6.

I have of course did the usual Deoxit on the wafer switches, clean them carefully and the unit is in great - but dusty - condition. I just need to hear a radio in there before I get too deep as I am way to busy to get pulled into a restoration activity.

Any advice would be great if you swam around the insides of one of these. I worked on and re-caped a museum-grade SX-16 my dad has and was hoping this was like that. I have three SX-28s to pick from but I want this one working as the SX-16/SX-17 are great performing sets for what they are and pretty cool!

Right now My 1K resistor goes bye-bye in seconds with only the rectifier tube in. This resistor is coupled to ground via a couple components: The coupled 10Ks and 25uF/400 I cannot locate in it as to the schematic I have. There was NO 25uF as specified by schematic and book. And the replacement of caps was simple enough and I kept it clean and did it in a couple sittings to do a great job (this one is MINE :-) ). The Riders early and late schematics do not exactly match the original Hallicrafters SX-17 book schematic I have with the unit.

Note: the 1K in question no longer looks like its a 1K: the color bands fade when the metal oxide resistor gets hot. Understandably I don't let it do that very long before I shut it off.

Thanks!!


Last edited by mrrstrat on Sep Fri 17, 2021 3:48 am, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 3:41 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
This is where I *think* the resistor is. I can't say I like point-2-point wiring as much as a PC board but it is the only 1K called out in the schematic. The SX-16 has a 1K in this same spot.

Attachment:
IMG-7196.jpg
IMG-7196.jpg [ 410.56 KiB | Viewed 496 times ]


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 8:45 pm 
Member

Joined: Mar Thu 04, 2010 3:09 am
Posts: 127
Hello. No help on the SX17 but I am plodding thru an SX16 with good results and need some guidance from someone with SX16 experience.

Mine is clean but had a bad primary on the first audio stage transformer. That caused a 10k resister to smoke, raised the grid V on one of the 6V6 tubes to +27 VDC and shorted it out. I tried a mod I learned from a Philco model 20 cathedral radio using a .1 cap to bypass the primary completely and it worked! Great audio and happy 6V6 tubes.

Here is the last big issue... The AM broadcast band is pretty much dead while the radio works better than expected on the shortwave bands after just a minor alignment. I connected the antenna to the grid cap on the 6L7 mixer tube and the AM band boomed in. However, as expected, with the antenna connected there the SW bands die out.

I also tried connecting the antenna lead to the grid cap of the 6K7 RF amp. No luck. That leads me to believe the issue lies in the selector switch after that section. The problem lies in the placement of that 6K7 as the socket sits beneath the really busy rack with the selector switches and coils plus a few tightly placed wax caps so I cannot get to it safely with a meter probe to check the voltages.

Since the radio works so well otherwise I fear that I may make matters worse if I really dive into that tight spot. As I am slowly replacing caps and bad resistors I likely will leave the wax caps in the bad places alone.

With that background and your experience with SX16s do you have any thoughts?

Thanks, Rich


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 10:14 pm 
Member

Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
I finished up my SX-17 not long ago. I have multiple pictures of the bottom. The first few will give you a taste of what I did -- the last few my hone in on your problem area.

Attachment:
IMG_0623.jpeg
IMG_0623.jpeg [ 161.89 KiB | Viewed 414 times ]


Attachment:
IMG_0639.jpeg
IMG_0639.jpeg [ 108.02 KiB | Viewed 414 times ]


Attachment:
IMG_0670.jpeg
IMG_0670.jpeg [ 149.51 KiB | Viewed 414 times ]


Attachment:
IMG_0673.jpeg
IMG_0673.jpeg [ 160.77 KiB | Viewed 414 times ]


Attachment:
IMG_0650.jpeg
IMG_0650.jpeg [ 170.21 KiB | Viewed 414 times ]


I have been combing through all of my pictures (and I took a many many so I could get it all back together properly)... but I cant seem to find any that show R39 any better.

It was worth all of the effort... works well now and I learned a lot along the way.

Attachment:
IMG_2091.jpeg
IMG_2091.jpeg [ 159.68 KiB | Viewed 413 times ]


Let me know if I can be of any other help.

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 10:42 pm 
Member
User avatar

Joined: May Sun 22, 2011 11:27 pm
Posts: 409
Location: Dallas,TX
Gasman,

That is one of the nicest restorations that I've even scene on an old Hallicrafters. Anyone would be proud to own that receiver. Great job!

Mike

_________________
KE5YTV


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Fri 17, 2021 10:57 pm 
Member

Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
I have played with the jpeg photos that I previously attached and "zoomed" around a bit on them and captured this screen shot that might be useful. I can't seem to figure out how the jpeg files that are up loaded to the Forum can be manipulated and zoomed in on. This screen shot was taken from a zoomed in portion of IMG_0670.jpeg (before it was up loaded).

If needed I can send the jpeg files via PM and perhaps you can zoom in on those files.

BTW I am looking for a good candidate SX-28 or SX-28a to restore... how the heck did you come by 20 of them to restore?

Attachment:
Screen Shot 2021-09-17 at 2.48.07 PM.png
Screen Shot 2021-09-17 at 2.48.07 PM.png [ 1.28 MiB | Viewed 409 times ]


John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 12:29 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
We seem to own the market on SX-28 and SX-28As these days. In the last 6 months we have bought up just about all of them around. I have 3 and one in parts now in the shop. They are surprisingly nice to work on. I think we have a dozen or more ready to go. The best one I think we had was one with a multi-tube calibrator in it. It was so sensitive that the band spread needed a few mils of movement to find other stations/signals. It was the first time I had a tube radio that the dial mechanism was way below the ability of the tuning circuitry to bring in stations.

On my SX-17: I am pretending there is no issues with the IFs and other transformers at this time. I am hoping it is some easy fix I am overlooking.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 12:37 am 
Member

Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
If you have restored 20 SX-28s this should be a cinch :D

It's hard to troubleshoot when it blows the resistor before you can even check any voltages. Let me know if I can help. Don't buy up all of the SX-28s before I find one!

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 12:50 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
You would think - but its hard to calmly measure where the voltages are going when the 1K starts turning orange lol.

The SX28 is not that bad to work on. A lot of repairs are mechanical on these on occasion. Its amazing that I have about everything written on the SX28 for repairing them and nothing that addresses the Lamb Silencer portion to set the transformer. I figured out a process to tune this part of the circuit.

The last thing like the SX-17 I worked on was my dads SX-16. Completely replaced all caps and resistors and it is in perfect condition. Its his favorite toy and reception is out of sight.


Gasman wrote:
If you have restored 20 SX-28s this should be a cinch :D

It's hard to troubleshoot when it blows the resistor before you can even check any voltages. Let me know if I can help. Don't buy up all of the SX-28s before I find one!

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 1:02 am 
Member

Joined: Mar Thu 04, 2010 3:09 am
Posts: 127
When I was troubleshooting the audio circuit in my SX16 last month the 10k 1/2 watt res cooking fast. Just to get a starting point I put in a much larger resistance rated 5 watts to give me time to measure some voltages. Everything up to the first audio stage was fine so it led me to the first stage audio transformer primary.

Rich


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 1:28 am 
Member

Joined: Mar Wed 16, 2011 10:44 pm
Posts: 2033
Location: Peekskill, NY
There's an excellent write-up on the lamb noise reduction circuit that's available.

My 28A had extensive mods made to that and it took a long time to get it back to stock.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 1:39 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
I think I have a line on the issue: a hint given to me help locate the coupled 10K resistors and "missing" 10uF/400. The guy pointed out the missing 10Ks might be the terminal strip resistor along the back. I have never had problems with these in the past and largely ignored them (didn't know these were resistors!).

So it seems that this R3 and R4 measure no more than 5K per leg (half what they should). And the missing 25uF looks like it was replaced by me with a 0.22uF/600V Orange drop. The old caps were in very bad condition and I must have read the 25uF as 0.25. All schematics refer to this capacitor as a 25uF/400.

So it looks like wrong cap and the terminal strip is measuring one half of the value it should be.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 2:36 pm 
Member

Joined: Apr Thu 12, 2007 3:24 am
Posts: 2694
Location: Milwaukee WI 53219
Looking at the schematic, with tubes pulled the only possible thing I see to cause that resistor to burn would be a shorted bypass cap connected after it. Or a physical short from some connection touching another in the radio. In the schematic the voltage comes from the bottom of the resistor and with tubes pulled I don't see any other path to chassis ground other than that bypass cap connected right at the top of the resistor.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sat 18, 2021 4:46 pm 
Member

Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
forumuser wrote:
Looking at the schematic, with tubes pulled the only possible thing I see to cause that resistor to burn would be a shorted bypass cap connected after it. Or a physical short from some connection touching another in the radio. In the schematic the voltage comes from the bottom of the resistor and with tubes pulled I don't see any other path to chassis ground other than that bypass cap connected right at the top of the resistor.


Looking at the schematic (unless I am mistaken) with the tubes out it could short out via the bypass cap (R-84) like Forumuser suggested or via a shorted out C76 through R8.

I would think it would be possible to check the resistance to ground in that path (with the tubes out and the power off) and see what it actually is and then work backwards in the circuit to see where the big drop in the resistance is. It is also possible that one of the windings on one of the coils has shorted out.

You probably already checked the resistance to ground along that circuit path but in case you haven't ...that is what I would do next. Along with double checking the wiring to make sure it is wired correctly.

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sun 19, 2021 4:29 am 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
All good information: the set is a one-owner set. The guy bought it new, never worked on it but it was kept pretty well. Not like climate controlled but next best thing. He assured me he never worked on it or modified it - which is good. When I get these in the shop I assume nothing is off the table. And I have seen everything. My SX-43 and SX-25 I have were project radios for some weekenders that got in over their heads. The SX-43 was a complete gut and rebuild (everything inside replaced and corrected complete sections of it. My SX-25 had a very overrated power transformer installed and an elaborate grid of Ohmite resistors someone used to try to bleed off 75 or more volts. Didn't work and I restored it back to stock with an appropriate PT I spec'd. It is my best receiver.

Once in a while I get one that throws me for a loop - this one has something wrong I have not fixed before. Its happening so early in the power flow of the circuit you would think it jumps out what is wrong. But like most mysteries some simple block and tackle technician work will solve it.

I am ALWAYS open to help and even at my stage of the game I consider my self still learning. There is always someone who knows something better and I am glad to take the help :-)


Gasman wrote:
forumuser wrote:
Looking at the schematic, with tubes pulled the only possible thing I see to cause that resistor to burn would be a shorted bypass cap connected after it. Or a physical short from some connection touching another in the radio. In the schematic the voltage comes from the bottom of the resistor and with tubes pulled I don't see any other path to chassis ground other than that bypass cap connected right at the top of the resistor.


Looking at the schematic (unless I am mistaken) with the tubes out it could short out via the bypass cap (R-84) like Forumuser suggested or via a shorted out C76 through R8.

I would think it would be possible to check the resistance to ground in that path (with the tubes out and the power off) and see what it actually is and then work backwards in the circuit to see where the big drop in the resistance is. It is also possible that one of the windings on one of the coils has shorted out.

You probably already checked the resistance to ground along that circuit path but in case you haven't ...that is what I would do next. Along with double checking the wiring to make sure it is wired correctly.

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sun 19, 2021 7:26 pm 
Member
User avatar

Joined: May Wed 20, 2020 1:33 am
Posts: 400
Location: Rockford, IL
We have a winner: its C76 and its partner - the other coupled 10pF - that were the offenders. While I have thousands of caps and resistors, 10pF seem to go fast. Testing showed some strange behavior for a cap - removing them prevented the 1Ks from going exothermic.

I had several attempts to get measurements - probably more than I should have. The little caps below were the offenders.

Attachment:
IMG-7204-parts.jpg
IMG-7204-parts.jpg [ 500.42 KiB | Viewed 298 times ]


I had only a handful of 10pFs and used 6.8pF/1kV instead. I cannot see how an 80 year old radio will care about a few pFs either way.

Attachment:
IMG-7198-rep.jpg
IMG-7198-rep.jpg [ 827.79 KiB | Viewed 298 times ]


Attachment:
IMG-7199-rep2.jpg
IMG-7199-rep2.jpg [ 713.25 KiB | Viewed 298 times ]



So I put the tubes back - most of them some of the pick of my litter - I fired it up and found a radio.

Attachment:
IMG-7202-rad.jpg
IMG-7202-rad.jpg [ 473.37 KiB | Viewed 298 times ]


Attachment:
IMG-7200-test.jpg
IMG-7200-test.jpg [ 875.63 KiB | Viewed 298 times ]


I measured at the site of the failure - about 245VDC and the other meter is checking chassis voltage (on or off plugged in is a nice 1.00VAC or so).

Not bad reception considering it needs a good alignment and the strings re-did. Tunes sharp, Xtal works but BFO is weak (again:alignment).

So now I'll clean it up and work on the details before I align it. And I want to replace those original dual 16uF filters first..

Thanks for the help - sometimes it takes someone to point out something obvious but it always helps in the end :-)


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Sun 19, 2021 8:02 pm 
Member

Joined: Jun Sat 18, 2011 5:14 pm
Posts: 313
Location: Washington State 98226
Way to go -- persistence pays off!

John w.


Top
 Profile  
 
 Post subject: Re: ** SX-17: need pix of the insides! **
PostPosted: Sep Mon 20, 2021 1:11 am 
Member

Joined: Mar Wed 16, 2011 10:44 pm
Posts: 2033
Location: Peekskill, NY
See the story in the SX-11 threads about the BFO injection gimick. Often this needs to be increased to read SSB signals.


Top
 Profile  
 
Post New Topic Post Reply  [ 28 posts ]  Moderator: Sandy Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 11 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB