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Author Topic: National NC-173 Question -  (Read 2203 times)
KH6KM
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Posts: 6




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« on: January 04, 2013, 08:10:48 PM »

Hello all,
I recently acquired a very nice National NC-173 receiver that suddenly stopped working and I need some advise to get me going in the right direction. The receiver worked fine for two days after it's arrival to my QTH out here in Hawaii. The next day, the receiver was again turned on and I noticed that there were no signals to be heard, just the normal hum of the audio. I could fairly well tell that the controls such as AF Gain, RF Gain, the Selectivity control etc. all seemed to function but no signals coming through. After investigating further and playing around with the main tuning and bandspread dials, I discovered that there is a small window of several hundred KHZ from approximately 9 KHZ down to about 6 KHZ where signals are heard. This is on band "C". If I tuned past these approximate frequencies in either direction, the receiver would again go dead. All other bands, including the standard broadcast band are dead. I suppose one could suspect a tube gone bad suddenly and I could try changing out tubes but it seems to me that the fix might not be so simple. I also might add that this receiver was completely gone through and restored by W1RY recently.
If anyone out there has any experience with this kind of trouble or has any suggestions, I would appreciate it.
Also, I wanted to mention that the "Selectivity" control on the upper right hand corner of the receiver feels "floppy" to me and not solid like the other knobs. It does function okay, as I was using it when the receiver was working. It just seems to me that it should have a more solid feel to it. If anyone else has a NC-173 out there and could let me know if this is normal or if something needs fixed there, that would be great!
Thanks for your help. This receiver is too nice to just let it sit in the corner and not be used.

73,
Kelly  KH6KM
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KE3WD
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Posts: 5694




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« Reply #1 on: January 05, 2013, 07:29:36 AM »

Clean and lube all switches and controls except for Main Power switch using Deoxit or the likes before doing anything else. 

You likely have moved the old girl to a completely different climate.  I remember how my 1545 uniform shirts never seemed to get thoroughly dry down at Hickam.  Also remember how the humidity in Thailand made Hickom seem like we'd left a desert. 

But, back on point, the application of Deoxit plus immediate excercise of every switch and control, before the good stuff evaporates away, has cured more appliance problems than a lot of folks without seeing all those pieces pass over testbenches will believe. 

Always should be done before anything else in the way of repair attempts should be considered. 

At the very least you will know that any problem is not due to resistance buildup in contacts, etc. 


73
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W9GB
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Posts: 2611




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« Reply #2 on: January 05, 2013, 08:57:29 AM »

Quote
The receiver worked fine for two days after it's arrival to my QTH out here in Hawaii. The next day, the receiver was again turned on and I noticed that there were no signals to be heard, just the normal hum of the audio.
Overseas Shipping (air or ship) exert a number of shocks to equipment (even well packed).
A marginal tube may have failed after a couple days of operation.
Quote
This receiver was completely gone through and restored by W1RY recently.
Restoration work covers simple replacements of failed/worn out components to complete rebuilds from chassis up.  The later is quite expensive in labor (time) and parts (new).

Have you called Ray Bintliff, W1RY at Beta-Tek Antique Radio Service?
Ray Bintliff, 2 Powder Horn Lane, Acton, MA 01270.  978-263-7435.  E-mail w1ry@msn.com

James Ollinger's NC-173 Adventure
http://www.jollinger.com/radio/projects/nc173/nc173.html
« Last Edit: January 05, 2013, 09:26:33 AM by W9GB » Logged
KB4QAA
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Posts: 2323




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« Reply #3 on: January 07, 2013, 12:26:49 AM »

I have an NC-173 that is a work in progress.

** Do NOT slobber Deoxit all over the rotary wafer switches!!!!!

The phenolic will absorb the solvent and swell, making the switch stiff or impossible to turn.  It takes the better part of a year for it to evaporate and return to normal size.  (Ask me how I know)

Use a cotton swap to carefully apply the Deoxit to just the metal contacts.

A pipe cleaner moistened in Deoxit can be used to clean the tube pin receptacles.


I do not think there is an easy one-shot fix.  Have the paper and electrolytic capacitors been a replaced?   If not, don't power the radio up until you have done so.

The selectivity knob is loose as well on mine. It leads into an enclosed compartment.  Further investigation needed.

good luck.
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KE3WD
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Posts: 5694




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« Reply #4 on: January 07, 2013, 05:35:33 AM »

That is a very good point that should be heeded not only as regards the National wafer switches but also for any and every application of something like Deoxit, no matter the era or age of the unit on the bench. 

I'm always saying, "a wee bit" of Deoxit in posts, but there is this American Male situation whereas we are testosterone poisoned guys who often figure that if a little bit of something is good, then a lot of it is "mo' better".  Not. The. Case. 

A very tiny ampount of Deoxit goes a long, long way. 

TIP:  They also market a small vial of "Deoxit 100%" formula that is not packaged as an aerosol spray.  Comes in a tiny squeeze bottle.  This stuff is excellent for use in places like the contacts of said wafer switch and use of a toothpick as applicator and very tiny amount of the stuff applied just at the location of the contacts themselves works very well indeed.  Alternatively, the standard aerosol can stuff may not be as concentrated, but spraying a wee amount into the cap or some other tiny container like the cap will allow the wetting of said toothpick or other applicator used to transfer the good juice to just the spot where it is needed. 


73
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KD0FAT
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Posts: 64




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« Reply #5 on: January 07, 2013, 05:49:06 PM »

My 2 cents worth:  Your receiver works fine on part of one band---this means that the RF path, the IF path, and the audio path are functional, but not on all bands, and not on a full band. The tubes, caps, resistors, etc. are ok.   I suspect that oxidized contacts on the bandswitch are blocking the other bands from functioning. Looks like time for judicious application of Deoxit.  The limited function of the receiver on one band may indicate a poor contact by the wiper in the main tuning capacitor. Another place to apply Deoxit. Best of luck to you, and I wish that I had a NC-173 to play with!  73, Al.
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KH6KM
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Posts: 6




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« Reply #6 on: January 07, 2013, 08:26:31 PM »

I appreciate everyone's comments. I hear the message on the Deoxit issue loud and clear. It seems everyone is pretty well on track to solving the problem. Since my first posting, I have some news to report. I took the wooden  handle of a paint brush and tapped on each tube in the receiver while it was operating in the certain little segment on band "C". When I tapped on the 6SA7 first detector tube, I was greeted with some nasty noise and the receiver went dead again. I pulled the tube completely out of the socket and inserted it back in. The receiver came back to life on all bands! Looks like all we have here is a dirty or corroded tube socket. I should have went straight for the tube sockets to start with. Seems like it's always a tube issue. By the way, the receiver has been totally recapped. As one responder had stated that it could be the band switch, I have fully tested it and it is working properly. What is really wierd to me is that a dirty tube socket that is causing the receiver to mostly go dead would still allow a small portion of one band to still operate normally. Anyway, I now can go after this tube socket with some Deoxit or contact cleaner and deal with it. As for the loose selectivity switch, I can get a glimpse of a nut that is loose on the threaded shaft. It must have worked itself loose during shipment. I'll be dealing with that next.
Thanks to everyone for responding with some very good suggestions.

73,
Kelly KH6KM
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KE3WD
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Posts: 5694




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« Reply #7 on: January 08, 2013, 07:12:24 AM »

Think about this:  The tube socket consists of two metals contacting each other to conduct electron flow. 

The contacts in the bandswitching do the very same thing, two metals coming into contact with each other to conduct electron flow. 

Both can suffer from the detrimental side effects of a change in climate (or a change in location to a different climate, which is accomplishing the same thing).

The clue I saw when I recommended cleaning switches first is that the darn thing worked immediately following the move, but only after working a few days or so it started to act up. 

Sometimes I've had to clean tube pins and the metal inside the sockets using cotton swab or toothpick with a wee bit of Deoxit on them in order to prevent having to go back in there every other week and get the contact to work again. 

Cleanliness is next to Godliness, so Ben Franklin printed.


73
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KH6KM
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Posts: 6




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« Reply #8 on: January 08, 2013, 08:39:01 AM »

KE3WD:
All well noted. Consider it done!

Thanks
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K3STX
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Posts: 971




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« Reply #9 on: January 09, 2013, 02:52:52 AM »

What is really wierd to me is that a dirty tube socket that is causing the receiver to mostly go udead would still allow a small portion of one band to still operate normally.

What is really wierd to ME is than an Antique Radio Restoration Service would send you a rig with dirty tube sockets.

Paul
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WN2C
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Posts: 438




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« Reply #10 on: January 09, 2013, 04:00:40 AM »

Could dissimilar metals cause the same issue...Pins on tube and the tube socket?

Rick  wn2c
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KE3WD
Member

Posts: 5694




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« Reply #11 on: January 09, 2013, 08:44:26 AM »

Could dissimilar metals cause the same issue...Pins on tube and the tube socket?

Rick  wn2c

Now, Rick is thinking like an forensics technician.

Or maybe that should read technologist.

Dissimilar metals can indeed cause corrosions, with enough buildup that translates to unknown resistances and in some cases even acting like diode junctions. 

Now consider that this rig was taken from one environment and suddenly dropped into another, namely the high humidity environment of the Hawaiian Islands. 

The higher relative humidity can certainly contribute to such problems, typically accelerating various chemical and electrochemical actions such as the meeting of two dissimilar metals can exhibit. 

Now consider the impact of such on one of the pins of a tube that does not carry any rather high potential, such as the grid or cathode. 

rust never sleeps,


73
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KH6KM
Member

Posts: 6




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« Reply #12 on: January 09, 2013, 09:01:48 AM »

Maybe I should rephrase my statement. First of all, the antique restoration service did not send the radio to me that way. It was purchased privately from another party after the fact. Secondly, the radio endured a very long transit out here to Hawaii and movement in tube sockets could cause things to happen. I said, "a dirty tube socket", which was a generalized statement. What I should have said is that it also could have been affected by the change in humidity or perhaps just a pin not making proper contact after the long boat ride. I really can't say. Bottom line is that all is working okay now!

73,
Kelly KH6KM
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