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 Post subject: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 2:21 pm 
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Been working on it part time for a few weeks, and now and there seems to be a problem with the front end RF tuning.

When setting the upper/lower band edges, the RF Amp input inductor on all bands seem to not to tune properly in that they don't have a definite peak, and, all want the movable loop to be adjusted toward the end of adjustment at "max L" I think. Sensitivity is poor, with 10db S/N being around a 2 to 3 uV, interestingly, the higher bands have the better sens.

The capacitors, either the GC (general coverage) or BS (band spread) tune as would be expected with a sharp peaks.

Haven't done much investigation yet, and since its common to all bands, I'd suspect the problem is not in the catacomb. I'm thinking maybe someone else has seen this before and can offer the solution.

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Last edited by Mikeinkcmo on Nov Sun 12, 2017 5:08 pm, edited 1 time in total.

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 3:23 pm 
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Mike,

I haven't run into that issue with any of my moving coil catacomb receivers but I agree that it isn't likely to be in the catacomb since it is happening on multiple bands. It is also curious that Q in the circuit seems to be OK since the adjustable C is showing the normally expected peak. I am not a fan of these loop tuned coils and they are especially painful when trying to sort out issues especially if someone has been in there before you and already stressed that shorted turn loop near its breaking point due to wire fatigue.

Do you have one of the "magic wands" in your alignment tool set that has a ferrite slug in one end and a brass slug in the other? If so try it in the coil and see if that shows a sharp peak.

I don't know if it could impact the L more than the C adjustment but take a look at the 5,000 pf cap that provides the ground for the RF stage variable capacitors; I expect leakage here could cause some odd behavior.

Good luck and we look forward to your findings!

Rodger WQ9E


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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 5:08 pm 
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Thanks Rodger. Ya know, I've completely forgotten about those wands. Don't have one and haven't for I don't know how many years/decades, Off to the bay to get one. Thanks.

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 7:27 pm 
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Mike,

You are welcome and they do come in handy. It is worth a shot to see whether the coil response appears fairly sharp as the inductance is varied.

Did the radio look any dirtier than is typical for older gear inside? Maybe something got around the fixed contact section for the sliding coil cat and is causing leakage/loss of Q. Hopefully it is something simpler than this so that you don't have to pull the catacomb although it really isn't a terrible job and I believe you have done this before.

Rodger WQ9E


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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 8:08 pm 
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Rodger, go HERE and take a look. It wasn't too awfully dirty but I wasn't going to work on it till I got it cleaned up.

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Fri 10, 2017 10:51 pm 
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Mike,
That one cleaned up VERY nicely!

Rodger WQ9E


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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Sun 12, 2017 4:04 pm 
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Location: ST Paul, MN
I am in the process of ordering replacement caps for my 2-40D can you tell me what size the opening of the stud mounted caps is? Are the 3/4" or 7/8"?

Thanks and 73
Kevin - KG0MN

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Sun 12, 2017 5:30 pm 
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Quote:
...can you tell me what size the opening of the stud mounted caps is?
If you are going to replace them, just pull them and measure the stud.

I just left the two cans in the radio and put modern caps under chassis.

Image

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Wed 22, 2017 6:25 am 
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Rodger, you were spot on!!

As you can see in the pic's extreme upper right corner, there is only ONE cap that hasn't been replaced, C2. Don't know how I missed that one, but I picked up about 8-10db of sens, and the input coils now peak. Not as sharp as I remember from other Nationals, but at least now there IS a peak.

Image

Thanks for the help.

Its on the radio bench replacing the HQ129X, and the Ranger is next on the repair bench.

Mike

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Wed 22, 2017 3:33 pm 
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Mike,

Neat work and I am glad you found the problem.

The sliding coil catcombs are pretty easy to recap given the easy access but I did see a NC-100X for sale with the sign (partially recapped but needs recapping). The owner had recapped it by switching bands to move the catacomb but he had mounted the replacements sitting up so that the catacomb no longer cleared them :) The radio was cheap and I bought it because a friend was looking for one.

Rodger WQ9E


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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Sat 25, 2017 12:46 pm 
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No wonder it was "cheap". Amazing what can be found at fests.

Went looking for the tuning wand and so far, regardless how I query, no luck. Interesting, but it'll show up sooner or later.

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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Sat 25, 2017 2:46 pm 
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Mike,

You may have to make your own. A slug of ferrite in one end (probably the tuning slug out of an older 10.7 Mhz IF transformer would be a good mix) and a slug of brass in the other end of a plastic tube. One of the old Heathkit "nut starters" would provide a good basis for one.

These are the sorts of things you would find in a "box of junk" at a hamfest.

Rodger WQ9E


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 Post subject: Re: NC-2-40D alignment problem?
PostPosted: Nov Sat 25, 2017 10:41 pm 
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Quote:
These are the sorts of things you would find in a "box of junk" at a hamfest.
Absolutely right!!

Those Heath nut starters are a great little tool. I always take a cursory look through the boxes of grubble, both on and under the table. I found a complete set of SX-28 knobs including the original spoked tuning knobs for 8 bucks, when the two tuning knobs alone were going for $35 plus on ebay.

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