[mikethedruid]

I just started work on my National NC-125, an 11 tube communications receiver. The manual and schematic can be found here: http://bama.edebris.com/manuals/national/nc125/  for those who want to follow along. This is how it looked when I first received it:

[Image: https://64.media.tumblr.com/7f56a0296e9b...922566.jpg]

When I got it, the main tuning dial had a problem which I quickly managed to fix, just a minor mechanical snag. Then I ordered a complete set of condensers for the radio from: https://hayseedhamfest.com/ . This guy is a great source of custom made electrolytic condensers which will fit into older radios and have higher specs than the originals. Now that I am finished with my SW-54 adventures, I got back to work on the NC-125. Today, to begin with, I replaced the one two section can. The work went very smoothly. Here are some pictures. First, the whole underside of the chassis before any work:

[Image: https://64.media.tumblr.com/21deea236ef7...315439.jpg]

Next, a close up of the underside showing the two section electrolytic before replacement:

[Image: https://64.media.tumblr.com/096115084e19...c9ee1b.jpg]

And last a close up of the underside showing the replaced two section electrolytic:

[Image: https://64.media.tumblr.com/c51f3be833c9...d18233.jpg]

I find the liberal use of rosin flux, applied with a little artist's brush, very useful in de-soldering and soldering, especially to large lugs. I make it by dissolving crushed up violin rosin in 91% isopropyl alcohol from the dollar store.

[mikethedruid]

Work continues. I have begun to replace the paper and individual electrolytic condensers.
[Image: https://64.media.tumblr.com/f04443e0f04f...39c969.jpg]

[Arran]

I found some of those ceramic tube caps in a Hallicrafters S-120, which I though may have been responsible for the low volume, so I tried replacing one, an audio coupling cap I think, took the old one, tested it in a resistance-capacitance bridge, and it was fine all thw way up to rated volatge. So apparently they were installing plastic film, or paper mylar caps inside that style of casing by the 1960s.
Regards
Arran

[mikethedruid]

Finished the recap. Here is an overall shot of the chassis underside with all the paper and electrolytic condensers replaced:

[Image: https://64.media.tumblr.com/1bd89cce9329...4ca044.jpg]

There is a condenser , a .05 400v, that hides under the pot shown in the upper left corner of the over all picture. Here is a close up of it replaced with a .047 600v. :

[Image: https://64.media.tumblr.com/86220a82d70b...086cac.jpg]

There is one other tricky condenser to replace. It was a .01 400v hiding down under other components as part of the CWO circuit. :

[Image: https://64.media.tumblr.com/53dff7ca45bc...10ff78.jpg]

These were the only really tricky condensers to replace, the ones that required ingenuity and the hands of a surgeon, but they were not as bad as some I have dealt with, like the ones inside the tuning section of an old 37 Philco. Now that all the condensers are done, I will go on to check some of the carbon resistors and see how they look. If they are within tolerance I will go on to test the radio. Stay tuned......

[mikethedruid]

I checked the resistors and most were out of the 10% tolerance marked on them, while a few were just fine. I replaced all the ones which were out. Here is what it looks like now. Tomorrow I will give it its first test. Stay tuned...
[Image: https://64.media.tumblr.com/cde1508cfbf1...f1ca2d.jpg]

[mikethedruid]

Well... today I began testing, and there is good news and bad news. First I tested all the tubes, and I found that the audio output tube was very, very weak, tested bad, but with a tiny bit of life, if you know what I mean. I replaced that. The 0A2 also tested bad, but when installed it delivers the proper 150v regulation, so I am not going to worry about it. The good news is there were no explosions, and everything seems to actually be functioning. The bad news is that somebody has been into this thing and screwed around with the IF transformers. The IF is WAY off, so I am going to have to do a full and careful alignment. It is really pretty though when it is all lit up. I did have to replace the #47 bulb in the S meter, but the other one for the main dial was good.

[mikethedruid]

It's finally done !!! The IF alignment was not too bad. Fed 455 into the grid of the mixer/oscillator, and reset all the IF transformers, going over it twice and both ways. It is peaked out so any adjustment lessens the tuning, so... that is that. Then came the overall alignment of the 4 bands. That proved to be a bigger pain in the a$$. I ended up having to pull the chassis out of the main cabinet body, something I really wanted to avoid. Then I went to work. The manual is not really clear, and it took a LOT of trial and error to finally get the hang of what affected what, and how it affected things. The diagrams in the manual from BAMA, the only one I could find, are not really clear sometimes, especially the illustrations, so it is a bit of guess work to figure out which coil is which. There were times that the air turned blue and then I took a little break and played with my dogs, and then went back to work. At any rate it is done, and proves to be a good performer. Tomorrow I will put the chassis back into the cabinet, and button things back up. Then I'll take some final pictures of the radio in action.

[mikethedruid]

Today I did the last thing which needed doing as far as the repairs went. I replaced the old hardening line cord which surely does not have long to live, despite not having any cracks in it yet. After that I wrestled the chassis back into the steel cabinet. This unit is not like the old Hammarlunds which were made to be rack mounted or in a cabinet, and so are a piece of cake to remove and replace. These NCs take a bit more complicated maneuvering to get everything to come out, and then go back in. Still, I got that done. I then took it to my living room, and hooked it up to my antenna and the speaker I use for main listening. The radio works VERY well, as well, or a hair better then my Lafayette HE-30, definitely better on the highest frequency band, where, even in the daytime, I was able to receive short wave stations in range just above 15 MC, and the one above 17 MC. Most receivers get pretty deaf up there. So, here is what the finished product looks like working...

[Image: https://64.media.tumblr.com/794a37708c0e...010eae.jpg]

And here's a close up of the dial and S meter. I really do like the lurid glow. It is a very nice looking radio.

[Image: https://64.media.tumblr.com/76d5185f5eca...298545.jpg]

[EdHolland]

Very nice work Mike

[mikethedruid]

I am pretty tired today. Playing with the NC-125 last night I noticed that the 1.5 MC to 4.5 MC band was off. CHU Canada, which should have been at 3.33 MC was at 4.2 MC, so... back to the bench it went about 1 in the morning. After a great deal of fiddling around, I got the band properly aligned. Having played with this radio for a while now, the manual makes more sense, but it does take some playing and figuring things out. I finished about 4 in the morning, and re-tested the radio. That band now works REALLY well. I got CHU right where it should be, louder and clearer than before. I also got WWV at 2.5 MC, which is difficult because of the power lines over my pasture. I am very pleased, but I think I am going to do a little more tonight. I am going to leave the radio where it is, hooked to my main antenna. All the bands are properly aligned as to frequency, but I think I may be able to tweak the RF amps just a hair more on the other bands than the one I did last night. It will be pretty easy though. There is a little plate on the bottom cover which is held by 2 screws, and under it I can access the proper variable trimmer condensers. Anyway, I finally went to bed at 6 AM, and my dogs woke me at 8 AM. needless to say I am pretty tired. I may take a nap in a little while.

[mikethedruid]

I did some final tweaking this evening, and have all the bands peaked up. This radio is pleasing me more and more. The shortwave bands are ALIVE on this thing. There are really a LOT of stations, more than I have heard on my other radios with this antenna. I have not tried the Hammarlunds on it yet, and I think I will probably replace at least the electrolytic filter condensers before I do. Both radios are bone stock original as of now. Tonight I was listening to a very strange music program in English on about 6.2 MC. It was not a strong signal, and faded in and out a bit, but was always audible, and most times understandable. I tuned it in just after 12 AM Eastern Standard Time, and it went off at 1 AM. They played a lot of different, very odd songs ranging from reggae to jazz. There was also a rant by some guy with a lot of cussing, which surprised me. I actually liked it because of its oddity. Unfortunately I did not hear them identify what station it was, or give the exact frequency. If anybody else has heard this station, and knows what it is, let me know. Maybe it was a pirate broadcast. That might account for the cussing part. Sure was interesting and passed an hour away while I downloaded a lot of Jean Shepherd programs.

[mikethedruid]

The past couple of days I have been working on a video about the restoration of this radio. It is the first of two. This one is a narrated series of still images. The next will be a live demonstration. Be gentle. I am not a professional video maker.
https://www.youtube.com/watch?v=mWgw8aQk-_Y

[Radioroslyn]

Good Job Mike! [Image: https://philcoradio.com/phorum/images/sm...humbup.gif]
Moves along at a good pace, some vids I have to click on that little gear thingy and put it in high (2.0) [Image: https://philcoradio.com/phorum/images/sm...prised.gif] Pleasant speaking voice w/o a strong accent that takes a 6H6 to sort out.

The manual for my NC-46 and '173 are the same just not very clear and lacking contrast. Typically the rf adjustments are set up in rows making it pretty easy. Sometimes if I get lost I just push on the trimmer and see if it effect the band I'm aligning.

Probably preaching to the choir. Be looking forward for the next vid...

[Eliot Ness]

I agree, you did a good job without going off on tangents so it was a pleasant video to watch

I only have two very minor suggestions:

1. It would have been nice if you had photographed the Hayseed capacitors before installing.

2. When describing the location of components, such as the hard to replace capacitors, it would have been nice if you had placed red arrows on the pictures pointing to them. A simple program such as IrfanView makes that task very easy.

Looking forward to the live demonstration!

[mikethedruid]

I have used IRFANVIEW for years for basic editing of JPGs, but I have no idea how to use it as a drawing program. I figure my description of where the condenser is located in the picture should be good enough for people of average intelligence to figure it out.