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Old 17th Sep 2021, 2:39 pm   #1
mrrstrat
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Default Hallicrafters SX-17 Advice on repair.

I was able to snag this set from a guy who bought it new and was the 1 owner. He used it until about 35 or so years ago and stored it rather well - nice set and he has the distinction of being one of the developers of the Cray Computer here is the USA. So this set is doubly cool

I did the normal thing with a nice condition set: careful DeOxit on switches, check and replace tubes, look for evidence of issues.

The crayon capacitors looked particularly bad so I carefully replaced them and weak looking dog bone resistors. I recently completely restored a SX-16 and that set was fantastic so I was hoping the same from this one.

I normally do not have a non-working set from the start in sets in this condition, but on slow power I had a resistor smoke and die. I am very certain my soldering is solid and did each one at a time to prevent confusion - and did so on a few different sittings as to not get 'fatigue restore syndrome' and rush it.

My set is a later model SX17 - evidenced by the 6H6. I do have the original manual and schematic - even still some things to not appear to exactly match from what I have seen inside and the original owner assured me he never worked on it.

I have some pix and circled the resistor in question - I looked at the schematic located the resistor - I believe it is the only 1K the SX17 has and is R39. The place it couples to ground is a coupled 10K/10K and a 25uF/400. I do not seen any evidence of the 10uF and am not absolutely sure where this cluster of parts is in my set. Point-2-point always stimeys me as I like PC board layout with its orderly and easy to follow layout.

I am not sure why with just the 5Z3 (rectifier) in the set this resistor still wants to glow and burn out. Previous trials I had all tubes and would replace the 1K so I could do some measurement of voltage to see what is going on.

Perhaps someone has been down this path? Any assist is most greatly appreciated.
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Old 17th Sep 2021, 2:41 pm   #2
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Default Re: Hallicrafters SX-17 Advice on repair.

I have pix - and tried to keep everything as tidy as possible as this set joins my fleet

- Rectifier voltage and power appear good and normal.
- No 'janky' solder connections or damage found in set.
- Valves were all TV-7 tested (calibrated tester).
- Voltage on resistor appears to be around 170VDC.
- Resistors I replaced were able to be identified 100% and validated the values.

The SX-17 is not most complex I have worked on (more than 20 SX-28/28As in the last 60 days) but this issue is not clicking with me on what's wrong. This set will be one that I will most cherish as it has some history and I have a nice PM-23 ('h' series) for it. My father has a SX-16 I restored and it is an amazing set. He listens to it every day and for hours per day. This set is preemptively part of my estate
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Last edited by mrrstrat; 17th Sep 2021 at 2:47 pm.
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Old 17th Sep 2021, 4:02 pm   #3
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Default Re: Hallicrafters SX-17 Advice on repair.

Used to have one of these receivers, mine was a good performer.

There's at least one error in the schematic I have, the error in a way concerns R39, anyone spot it?:

https://bama.edebris.com/manuals/hallicra/sx17/

Lawrence.
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Old 17th Sep 2021, 4:51 pm   #4
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Default Re: Hallicrafters SX-17 Advice on repair.

The Riders and the two schematics I have show the same thing for R39. The person who assembled mine may have been a part-timer who had no use for schematics - so I am still getting my arms around what is going on.

I cannot locate C48 and the existence of R3 and R4 :-(

Lawrence - I must have been absent they day they taught electrical engineering when I was in University so I am afraid I might be missing the point: perhaps you can illuminate us?



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Originally Posted by ms660 View Post
Used to have one of these receivers, mine was a good performer.

There's at least one error in the schematic I have, the error in a way concerns R39, anyone spot it?:

https://bama.edebris.com/manuals/hallicra/sx17/

Lawrence.
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Old 17th Sep 2021, 5:03 pm   #5
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Default Re: Hallicrafters SX-17 Advice on repair.

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Originally Posted by mrrstrat View Post
Lawrence - I must have been absent they day they taught electrical engineering when I was in University so I am afraid I might be missing the point: perhaps you can illuminate us?



Quote:
Originally Posted by ms660 View Post
Used to have one of these receivers, mine was a good performer.

There's at least one error in the schematic I have, the error in a way concerns R39, anyone spot it?:

https://bama.edebris.com/manuals/hallicra/sx17/

Lawrence.
Although there's no connection dot shown, one could be forgiven for thinking that the antenna input is connect to the 2nd RF amp's B+ supply via Range 6's antenna coil....

Lawrence.
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Old 17th Sep 2021, 5:10 pm   #6
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Default Re: Hallicrafters SX-17 Advice on repair.

Just looked - I would have thought it was connected too when I got past my R39 smoking issue.
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Old 17th Sep 2021, 7:01 pm   #7
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Default Re: Hallicrafters SX-17 Advice on repair.

Quote:
Originally Posted by mrrstrat View Post
The Riders and the two schematics I have show the same thing for R39. The person who assembled mine may have been a part-timer who had no use for schematics - so I am still getting my arms around what is going on.

I cannot locate C48 and the existence of R3 and R4 :-(
R3 and R4 might be the three terminal power resistor on the inside of the rear chassis apron.

Lawrence.
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Old 17th Sep 2021, 11:35 pm   #8
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Default Re: Hallicrafters SX-17 Advice on repair.

I wondered what that was - its a strange looking structure. I will check it out!

Thanks!

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Quote:
Originally Posted by mrrstrat View Post
The Riders and the two schematics I have show the same thing for R39. The person who assembled mine may have been a part-timer who had no use for schematics - so I am still getting my arms around what is going on.

I cannot locate C48 and the existence of R3 and R4 :-(
R3 and R4 might be the three terminal power resistor on the inside of the rear chassis apron.

Lawrence.
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Old 18th Sep 2021, 12:32 am   #9
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Default Re: Hallicrafters SX-17 Advice on repair.

I looked at the terminal power resistor - it does not measure 10K on each leg. It measures 5K. It will not produce 10K measurement in any combination including the ones the schematic dictate should. Also looks like some bloke put a .22uF where the 25uF/400 should go - so now the problem may be identified (I may be that bloke...).

Do these terminal power resistors go bad? I have a pair of Ohmite 10Ks and a large terminal strip (with a 22uF/450) I plan to replace this section with. I have no experience with these rather odd resistors intuit no repair I have done has ever involved these. Just making sure I am not overlooking something special about these resistors.
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Old 18th Sep 2021, 7:13 am   #10
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Default Re: Hallicrafters SX-17 Advice on repair.

I am not sure what you mean by "Terminal Power Resistor" as we use different terminology here in the U.S. for many parts. I did not see what you referred to in the photos.

If you mean it looks sort of like a solder tag strip with a metal case on it, those fail a lot. Typically the internal "fish paper" insulator fails and the resistance wire shorts to the metal casing/ ground internally That would certainly cause the "factory smoke" to come out. Often one internal section will open also.
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Old 18th Sep 2021, 8:51 am   #11
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Default Re: Hallicrafters SX-17 Advice on repair.

Quote:
Originally Posted by mrrstrat View Post
Do these terminal power resistors go bad?
The ones I had in my receiver's had at least one section go open circuit.

I would sort out the smoking R39 first, a short there would give the wrong resistance for R3 and R4 if measuring them in circuit.

In an annotated schematic I did years ago, a value of 0.1uF is shown next to C48.

Lawrence.

Last edited by ms660; 18th Sep 2021 at 9:18 am. Reason: extra info
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Old 18th Sep 2021, 12:52 pm   #12
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Default Re: Hallicrafters SX-17 Advice on repair.

Thanks Lawrence!

On the schematic documents C49 is listed as 25uF - I was sure I was better than that to miss that big. I probably saw .2 on the cap and replaced it with a 0.22.

On one section of the R3/R4 combo I am thinking I am safe to measure R3 in-circuit as its just terminal to ground. I get 5K and the same on the other section - I only was suspect because the value on both legs was nearly exactly half the schematic value.

The C49 now concerns me more - you are comfortable with the value being 0.1uF, I may have read the value on the cap as 0.2uF, and all schematics I have is 25uF/400. If you never had problems with 0.1uF I cannot see how the other values would matter that much - except the 25uF is excessive for what I normally see a shunted ground resistor (from my valve amplifier days).

I guess I am second guessing the terminal resistor - could it be just 5K on each? They are in series and identical wear is not out of the question but after nearly 80 years maybe its the substrate of the resistor finally broken down.

I am planning on replacing this with a pair of coupled 10K Ohmites on a terminal strip and was concerned the 5K might be what was originally put in.

The 1K R39 is easily replaced: I have hundreds of them at 1 watt and its a simple job - I wanted to fix what is making it draw the current that burns it up and it is decoupled from anything significant when set to band 6 - so the other end of the R39 to look at was R3/R4+C48. If those are wrong, I need to correct them.


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Quote:
Originally Posted by mrrstrat View Post
Do these terminal power resistors go bad?
The ones I had in my receiver's had at least one section go open circuit.

I would sort out the smoking R39 first, a short there would give the wrong resistance for R3 and R4 if measuring them in circuit.

In an annotated schematic I did years ago, a value of 0.1uF is shown next to C48.

Lawrence.
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Old 18th Sep 2021, 12:55 pm   #13
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Default Re: Hallicrafters SX-17 Advice on repair.

Yes - as Lawrence has indicated this is a likelihood. I have seen them ion many sets and thought they were a strange design terminal - learn something new everyday.

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I am not sure what you mean by "Terminal Power Resistor" as we use different terminology here in the U.S. for many parts. I did not see what you referred to in the photos.

If you mean it looks sort of like a solder tag strip with a metal case on it, those fail a lot. Typically the internal "fish paper" insulator fails and the resistance wire shorts to the metal casing/ ground internally That would certainly cause the "factory smoke" to come out. Often one internal section will open also.
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Old 18th Sep 2021, 2:07 pm   #14
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Default Re: Hallicrafters SX-17 Advice on repair.

I concur on the value for C48 - while it is notated as 25uF/400 in early schematics and documentation it is known as 0.1uF on the Riders documentation for both early and late models and the SX-16 has this capacitor as a 0.1uF as well.

It is likely I saw a 0.2uF paper/oil cap in its place and replaced it with a 0.22uF. The resistors R3 and R4 will be replaced.
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Old 18th Sep 2021, 2:37 pm   #15
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Default Re: Hallicrafters SX-17 Advice on repair.

If it's any help here's a link to the schematic I annotated some years ago showing component values, the annotated print seems to have faded a bit since I did it, not sure why that is, I also did one for the SX28.

Note: m = mica could mean mica or micamolds

Lawrence.
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File Type: pdf hallicrafters sx17 annotated 1pdf.pdf (304.9 KB, 16 views)

Last edited by ms660; 18th Sep 2021 at 3:05 pm.
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Old 18th Sep 2021, 7:39 pm   #16
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Default Re: Hallicrafters SX-17 Advice on repair.

This is great! Thanks for this

Also: I did replace R3, R4, and C48 with a slick turret board component and replaced the R39 1K. Same result: cooked resistor.



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If it's any help here's a link to the schematic I annotated some years ago showing component values, the annotated print seems to have faded a bit since I did it, not sure why that is, I also did one for the SX28.

Note: m = mica could mean mica or micamolds

Lawrence.
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Old 18th Sep 2021, 7:49 pm   #17
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Default Re: Hallicrafters SX-17 Advice on repair.

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Also: I did replace R3, R4, and C48 with a slick turret board component and replaced the R39 1K. Same result: cooked resistor.
I'm not surprised, I would have found out what's causing R39 to burn up first.

Lawrence.
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Old 18th Sep 2021, 8:20 pm   #18
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Default Re: Hallicrafters SX-17 Advice on repair.

Not much there to cause it: shorted cap or shorted coil. If its the coil that is game over for a while. Not sure about the coil as from what I can tell selecting a different band would "bypass" that coil and I cannot see where they are all shorted.
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Old 19th Sep 2021, 6:33 pm   #19
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Default Re: Hallicrafters SX-17 Advice on repair.

It ended top being a 10pF cap (C76 and the one coupled to it) that was drawing current and smoking my 1K resistors.

I did not have any good (new) 10pFs but lots of 6.8pF/1kV so I used them instead. Should not make a significant difference after all of the other parts are 80 years old.

Some advice here and another board helped - big thanks! Sometimes it helps to have people tell you what you don't want to hear: I was hoping that the problem was not in the coils and that subconsciously steered be toward not checking them .

I looked at the spent parts and had 5 attempts to try to measure voltage before they burned. Probably not the best idea but I have rebuilt sets before and needed to see where the voltage was dying. Some unpowered probing for resistance, loss, and continuity loss helped more than anything.
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Old 19th Sep 2021, 7:25 pm   #20
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Default Re: Hallicrafters SX-17 Advice on repair.

Great job and those caps will not fail again.
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