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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Thu 15, 2021 3:41 am 
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I dug mine out and popped the bottom off for the first time. One or two previous generations of owners have worked on it so as usual it takes some guesswork to determine what the original componentry was. I don't see your resistor in mine. Maybe it's there and one of the rest of you can spot it.

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EDIT: Ok, looking at it this morning I do have a resistor more or less where you have one. I cannot tell where your's is connected. The one in my radio is physically smaller but I am guessing that yours is a replacement. They don't seem to have the same color code but I don't know what to make of the code on the resistor in my radio.

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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Fri 16, 2021 3:43 am 
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Location: SE PA 19335
Khutch

Thank you!!! It's always helpful to have pics of other radios for comparison. :)

Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Sun 18, 2021 10:36 pm 
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Location: SE PA 19335
Jordan, et al, finally traced out the location (in schematic) of the mystery resistor. The 1st pic below shows the overall schematic and a red box around the general location of R?.

The second pic is a zoomed-in part of the schematic, showing that R? is wired in series with R23. Considering the relative size (ohms) 30:1 of these two resistors, I don't understand how the 100 ohm resistor could make any significant change in the circuit. Also, R23 is listed as .5W and R? is 2W.

Any theories out there?

Thanks, Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Sun 18, 2021 10:47 pm 
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Probably someone's attempt to monitor plate current.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Sun 18, 2021 11:09 pm 
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Joined: Apr Wed 01, 2020 7:22 pm
Posts: 330
If you've correctly traced it's location in the circuit, that resistor is of no use in the circuit, other than to possibly produce an IR drop across it in order to measure plate current as suggested...

Someone with an SX-25, or more experience with one might want to chime in here...!

73...Jordan VE6ZT


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Sun 18, 2021 11:18 pm 
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Joined: Oct Sun 12, 2014 1:02 am
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Location: SE PA 19335
That's what I thought, but I never considered using the 100 ohm as a current monitor.

The important thing is agreement that 100 ohms makes no difference in this circuit.

Thanks, Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Mon 19, 2021 2:44 pm 
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Your Ohmmeter will tell you but it could even be that some person with OCD found that the 3k resistor was only 2.9k so he "fixed" that. He used a 2 W resistor because that is what was in his junk drawer!

When I look at my photo on my cell phone my resistor seemed to have the color code bronze-black-red-or-is-that-brown which is not anything like the brown-black-brown 2 W resistor that you have. I could not easily tell from the photo where mine was in the schematic and since I had already packed my radio back up I could not easily trace it out visually. But now that you have done the detective work my resistor is clearly 3k and I am sure that 3k is just fine. Hallicrafters engineers were pretty good and this was not one of their build to cost radios, it was one of their upper tier radios, so if that resistor needed to be 3.1k that is what they would have specified.

Does the S-meter in your radio work? If not the 100 Ohm could have been a metering resistor for an external S-meter project that was never completed. Or maybe the owner just wanted a larger external meter. It is hard to say at this point.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Wed 21, 2021 12:50 pm 
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Location: SE PA 19335
khutch, et al

Can't say if the S-meter works, as the radio was not fully operational when I got it. Surprisingly, I did measure B+, and the values were about normal. Those old filter caps are now gone. All waxy caps replaced by film caps. :)

Still working on resistor replacement. 2W ones are complete and only a few .5W to go. Some SX-25 docs list 1/3 Watt resistors. I've never knowingly seen one of those. :?:

One road block I coming up - finding an original audio output transformer. I don't like the looks of the modern replacements. So I keep looking here, flea-bay, craigslist, etc., but no luck so far. :cry:

Best regards,

Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Jul Wed 21, 2021 3:48 pm 
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Location: Morris Plains, N.J. 07950
Frank, hamfests might be your best bet. Check into how many different Hallicrafters models used the same output transformer. Most hamfests usually have several Hallicrafters junkers from that era that would make perfect parts donors. I saw a couple last weekend for $20.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Tue 03, 2021 2:20 am 
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Location: SE PA 19335
I've been busy on this project - all of the components requiring replacement, wax caps, and most resistors. The old style 1 watt dog bones are nearly all gone. I find it amazing how small a modern 2W looks compared to them. They were all way out of spec, at least 30 - 40 percent. Same for the modern film caps compared to the old wax-paper or mica mold caps.

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This past weekend I attached and connected the tuning cap assembly. I was pleased by the results of the ultra-sonic cleaning. The connections between the tuning caps and coils are via holes in the chassis. There are both insulated an uninsulated wires. I covered all of them with sleeving to prevent shorts. There are also connections between the main tuning and band spread sections made with bare buss wire. I covered these with the smallest Teflon sleeving I had. This looks good and should last a long time. I attempted to reuse the braided ground connections, but found these so full of solder that they were no longer flexible, so I made up new jumpers and soldered them in place.

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I started testing tubes today, using my Heathkit TC2. Everything except the 6F6 audio output tubes tested in the green. The 6F6's tested in the middle of the yellow. Does that mean they will not function at all? I did not test the rectifier - 80 since the chart in my tester does not have this tube listed. Any suggestions?

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I replaced the audio output xfmr with a universal replacement but I don't like the looks. Hoping to find an original at a hamfest in Sept.

If all goes as planned I hope to apply rim bulb/reduced voltage later this week!

Best regards,

Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Tue 03, 2021 2:25 am 
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Joined: Oct Sun 12, 2014 1:02 am
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Location: SE PA 19335
if all goes as planned I hope to apply rim bulb/reduced voltage later this week!

should say DIM BULB!!! :lol: :lol: :lol:


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Tue 03, 2021 2:29 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 2808
You can replace 6F6 with 6V6 but in the yellow zone they should work okay. The rectifier is identical to a 5Y3 except for pinout. See tube manual for details.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 2:40 pm 
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Joined: Oct Sun 12, 2014 1:02 am
Posts: 346
Location: SE PA 19335
Hi all1
Went to a ham fest this past Sat. It was hosted by the Reading, PA amateur radio club. I went hoping to find an audio output xfmr for this SX-25 restore. I found some tubes for $1 each, and some HV mica caps for another project. I think I found the audio output xfmr, but it came with a complete Hallicrafters radio. I can't identify the radio. The dial says Super Skyrider, but there is no model number on the front panel and no nameplate on the backside of the chassis. However, it has twin 6V6 tubes and what looks like the xfmr I need. This radio is very cool looking and in very nice condition. I probably will not strip out the xfmr, but instead save it fo another restore.

See below. Maybe you can help me identify it.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 2:48 pm 
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Joined: Mar Thu 04, 2010 3:09 am
Posts: 127
That appears to be an SX16. There is a one 6v6 version labelled SX17. I recently acquired one for a fall project.

Rich


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 4:13 pm 
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Joined: Oct Sun 12, 2014 1:02 am
Posts: 346
Location: SE PA 19335
yahoomarine wrote:
That appears to be an SX16. There is a one 6v6 version labelled SX17. I recently acquired one for a fall project.

Rich



Thanks Rich

Is there any way to be sure what it is?


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 4:56 pm 
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Joined: Oct Sun 12, 2014 1:02 am
Posts: 346
Location: SE PA 19335
There were actually two other radios that I picked up at the ham fest along with the SX16/17.

One is an SX24 and another unidentified "Sky CHALLENGER" These were both in very poor condition, so at the get go I intended to use them for parts, mainly pwr transformers, switches, etc.

Can you identify this one

What is the purpose of the plug, 'MTR', shown in the bottom photo.

Thanks


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 5:00 pm 
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Joined: Oct Sun 12, 2014 1:02 am
Posts: 346
Location: SE PA 19335
Joe Connor wrote:
Frank, hamfests might be your best bet. Check into how many different Hallicrafters models used the same output transformer. Most hamfests usually have several Hallicrafters junkers from that era that would make perfect parts donors. I saw a couple last weekend for $20.


Joe, I picked up three radios last Sat. for $10. total.

See my latest posts.

Frank


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Wed 11, 2021 5:06 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 2808
MTR would be for an external S meter.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Thu 12, 2021 3:18 am 
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Joined: Feb Fri 13, 2009 5:09 am
Posts: 750
Location: Santa Clara, CA
The SX-16 is an 11-tube set, the SX-17 has 13 tubes (extra RF stage and noise limiter). They are both called "Super Skyrider", and have identical front panel layouts except the 17 has an extra toggle switch (noise limiter) in the lower right, between the Selectivity and Crystal Phasing controls. Yours appears to have a switch there, but it was a common spot for hams to "upgrade" and add a switch or pot in that location.

Both the 16 and 17 are push-pull 6V6 audio, but the dead give-away is that the 17 had a deeper cabinet, front to rear. They did not make longer decorative side stripe trim however, so the 17 decorations fall short of the back corner by over an inch.


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 Post subject: Re: Hallicrafters SX-25 restoration
PostPosted: Aug Thu 12, 2021 3:24 am 
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Joined: Feb Fri 13, 2009 5:09 am
Posts: 750
Location: Santa Clara, CA
The radio labelled "Sky Challenger" is actually the "Sky Challenger II" from 1938, and is designated either S-18 or SX-18, depending on whether it has the crystal. The original Sky Challenger was the S-15 or SX-15 of 1935, a rather more basic set.


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