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 Post subject: NC-109 Alignment Issues
PostPosted: Nov Sun 15, 2020 6:19 am 
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Joined: Feb Sun 16, 2020 7:45 am
Posts: 80
Greetings to the forum. I have an NC-109 that I am fixing up for my personal use. I have replaced the filter caps, all the paper caps, replaced the AC cord with a three-line cord and three-prong plug, added a fuse, and cleaned the bandswitch. Now I am trying to align it but having some problems. My equipment is a B&K signal generator, a B&K frequency counter, and a digital VOM. Realignment of the IF seemed to go well but the instructions in the manual for Alignment of the RF are not very detailed. I assume that the local oscillator is set 455 KHz on the high side for the lowest three bands A-C, and on the low side for Band D (14-30 MHz). I am using my digital IC-7300 receiver to measure the 6C4 local oscillator frequency by running a wire from the IC-7300 antenna connection to a point in the vicinity of the 6C4 tube socket.

For Bands A and B, the RF alignment seemed to go OK, but for band C (5 to 14 MHz), the instructions are to set the generator to 5.5 MHz, set the main tuning to signal, and to adjust the loops in L-1c and L-3c. I think I can can see the loops, but I have no idea whether they should be moved side-to side or up and down. Finally on Band D (14-30 MHz) the instructions are to tune L2 and L4 to maximum after setting the generator to 16 MHz. I found L4 but cannot find or recognize L2. Band D is absolutely dead. I can hear WWV at 15 MHz on Band C, but not on Band D.

Any suggestions would be appreciated.

Thanks and 73s,

Scott, N6CIC


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Sun 15, 2020 1:11 pm 
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Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7431
Location: Liberty, Missouri
Hi Scott,

Here is a pic of a couple of National front end coil "half turn loop adjusters". National Radio used this technique for decades. It was originally designed by James Millen, when he was chief engineer for National. This is the same James Millen who later started his own company and was famous for, among other things, his Grid Dip meters.

The purpose was to be able to adjust the inductance of coils, with out using tuning slugs, thus maintaining the "Q" of the coil. Trying not to deform them, you swing them in an arc along their axis. That is, the two holes where the wire enters the center of the coil form.

Image

If you swing the loop in one direction, the loop is going in the same direction as the other turns of the coil, thus, it adds to the inductance of the coil. If you swing it in the other direction its going in the opposite direction as the other terns, and it subtracts from the coil's inductance. Thus, you can "tune" the coil a small amount without a tuning slug, or, affecting the "Q" of the coil.

I use part of a bamboo skewer with a little notch in one end, for adjusting the "half turn" loops.

Adjusting them, you will find that as you remove the pressure of the tool, the loop will have a tendency to spring back toward it's previous position, so you will have to "over adjust" a little to compensate for that movement. They are a bit "adjustment sensitive" but after adjusting a couple of these loops you'll get a "feel" for the technique and it will become easy to adjust them.

The act of moving the adjuster back and forth will eventually make the wire brittle and it will brake, so keep that in mind. I've heard of that happening,However, I've worked on a lot of National radios over the years, and never had one brake. Just a bit of an FYI.
=====

As for finding L2, I can't provide any help, but, I'd certainly think it would be near the other two front end coils. Perhaps it shares the same "coil form" as one of the other coils.
=====

Can you hear the local oscillator on your 7300 when switched to band "D"? 6C4s are known for being problematic, having lower gain/output, and even becoming inoperative at higher frequencies.
=====

I'm sure others will comment soon, offering some NC-109 specific advise.

Good luck with your project.

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Mike


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Sun 15, 2020 1:51 pm 
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Joined: Nov Fri 30, 2018 11:16 pm
Posts: 539
Location: Ontario, Canada
Great info Mike I did know what those where, thanks for posting.

Skippy


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Sun 15, 2020 4:55 pm 
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Joined: Feb Sun 16, 2020 7:45 am
Posts: 80
Thank you Mike.

I now feel much better about adjusting those loops. Also thanks for the excellent photos! I thought I could hear the local oscillator on my 7300 on part of the D band, but need to check again. I also have a spare 6C4 I can try substituting. I will look again for coil L2, and perhaps someone else that owns an NC-109 will reply.

Thanks again!

Scott, N6CIC


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Sun 15, 2020 8:20 pm 
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Joined: Nov Wed 25, 2015 9:46 pm
Posts: 92
See this site: http://www.oldradios.50webs.com/nc109.html .

John VE3PMA


Attachments:
National NC-109 (1024x769).jpg
National NC-109 (1024x769).jpg [ 412.99 KiB | Viewed 388 times ]
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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Mon 16, 2020 6:33 pm 
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Joined: Dec Sat 28, 2019 4:18 pm
Posts: 557
Location: Corinth, TX
Mikeinkcmo wrote:
Hi Scott,
Can you hear the local oscillator on your 7300 when switched to band "D"? 6C4s are known for being problematic, having lower gain/output, and even becoming inoperative at higher frequencies.

Hammarlunds also have this problem, so it is not peculiar to National radios. If your problem IS the 6C4, a mil-spec 6C4WA/6100 should solve it.

John


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Tue 17, 2020 5:53 pm 
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Joined: Feb Sun 16, 2020 7:45 am
Posts: 80
Thanks John. I will try to order a mil spec 6C4WA.

Scott, N6CIC


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Tue 17, 2020 6:02 pm 
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Joined: Feb Sun 16, 2020 7:45 am
Posts: 80
VE3PMA John,
Thanks for the link which is very helpful for alignment adjustments. The National manual has no information, in contrast to the manual for the NC-98 which is complete in its detail.

73s, Scott, N6CIC


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 Post subject: Re: NC-109 Alignment Issues
PostPosted: Nov Thu 19, 2020 6:53 am 
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Joined: Feb Sun 16, 2020 7:45 am
Posts: 80
I replaced the 6C4 oscillator with a mil spec 6C4WA, and then went to work on Band D. In this photo (from http://www.oldradios.50webs.com/nc109.html), L4 is the small coil with a ferrite core. Attempting to adjust it was difficult because the coils must have been glued to the cylinder originally, and now after 60 years of so the coils kept detaching off of the cylinder. I know this is probably not a proper procedure, but I turned off the power and carefully held the cylinder while slightly adjusting the core, then removing my hand and turning on the power to hear the effect. I did this on WWV at 15 MHz. It took a number of iterations, but once I adjusted the core enough Band D came to life. L4 must have been badly out of alignment.

Thanks for everyones' suggestions!

73s, Scott, N6CIC


Attachments:
NC-109 Alignment-under chassis.jpg
NC-109 Alignment-under chassis.jpg [ 177.25 KiB | Viewed 260 times ]
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