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National NC 303




 
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Author Topic: National NC 303  (Read 1200 times)
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WD4DMZ
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« on: April 05, 2018, 09:27:51 PM »

The previous thread regarding good boat anchor receivers motivated me to go into my deep storage to fish out an NC 303 I got for a couple dollars at an estate sale a few years back. It is a true BA and I forgot just how heavy and large this thing is.

Before I put it in the shed I did clean it up, recap and give it a basic alignment. Also touched up the gray paint so it looked better than I remembered. It went from the bench to storage and I never tried it out on the air.

It is now in the shack and I have been using it the last two days and find it is a great AM receiver. Good audio, selectivity and the scale is very easy to use. It has the calibrator as well. Listening to CW is also good with the receiver. SSB is not as good as it seems to overload unless I turn down the RF gain. Anyone else notice the SSB issue with one of these? Maybe the alignment needs tweaking.

Very glad I pulled it out of the shed.

Rich

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nq5t
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« Reply #1 on: April 05, 2018, 10:10:03 PM »

An NC-303 graced my operating table for quite a long time.  It was electrically rehabbed, sweep-aligned, and was just a really great radio.  After a significant downsizing a couple of years ago, it was the one radio I really wish I'd hung on to.

In my experience, it IS necessary to back off the RF gain control a little to prevent a bit of distortion on stronger SSB signals.  There may be a way to correct it, but I tried a variety of things and nothing really worked.
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N1BCG
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« Reply #2 on: April 05, 2018, 11:07:24 PM »

We were fortunate to be able to use the NC-303 owned by Joe Walsh (Eagles) during the 95th 1BCG event on Dec 11, 2016. The ARRL set up his receiver and Valiant for the event’s AM station. Great receiver indeed!
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ns7h
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« Reply #3 on: April 06, 2018, 07:32:22 AM »

I have an HQ 170 that is also a classic boat anchor with the same need to reduce RF gain for strong signals.  I had one when I first got my general ticket in 1963 and did not recall that particular characteristic.  I think it was because the SSB activity was much less than AM or CW and wasn't a noticeable issue.  I moved on to the Drake twins for SSB later and do not remember the need for RF gain reduction to reduce distortion on SSB. 

Cool on Joe Walsh's NC 303. 

NS7H
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Carl WA1KPD
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« Reply #4 on: April 06, 2018, 07:45:17 AM »

Pretty much any pre mid 60s rcvr requires you to back of the RF gain in order to keep from overriding the BFO
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"Okay, gang are you ready to play radio? Are you ready to shuffle off the mortal coil of mediocrity? I am if you are." Shepherd
KA2DZT
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« Reply #5 on: April 06, 2018, 08:19:04 AM »

Pretty much any pre mid 60s rcvr requires you to back of the RF gain in order to keep from overriding the BFO


I agree with Carl,  I have to back off the RF gain on all my vintage receivers on SSB.
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K4CCW
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« Reply #6 on: April 06, 2018, 09:03:35 AM »

It's always been my understanding that with these receivers, to receive SSB properly, you crank the audio all the way up, and control volume with the RF gain control.

This seems to work on my many boatanchor receivers.

One exception is my HBR-16, where you have additional controls for mixer and IF gain. For that one, since I am old and don't use it often enough, I have to keep a cheat sheet handy to remind me how to best use the controls. However, properly used, it's a hot one!
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nq5t
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« Reply #7 on: April 06, 2018, 10:51:38 AM »

The 303 has a product detector, and AGC continues to run in SSB.  So it isn't like a lot of standard receivers of the era without product detectors where you have to turn off AGC, run the audio gain full on, and then fiddle with RF gain.  It's an SSB receiver.

You have to only back off the RF gain just enough to reduce the audible distortion.  If you do that, its SSB audio recovery is certainly clean enough, and you don't kill receiver gain in the process.
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WD4DMZ
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« Reply #8 on: April 06, 2018, 11:37:02 AM »

Thanks for the replies. Good info. Backing off the RF gain really cleans up the audio.

Another surprise found in the corner with stuff from the estate sale... I actually have the matching speaker.

As I continue to clean the radio up I find the gray plastic knobs are kind of flakey. There seems to be a chalky buildup that will not come off. It might be best to leave them alone for fear they might crumble. The three black knobs cleaned up just fine so the gray material must be made up of something softer.

Any ideas? I am afraid to soak them in soapy water.

Rich
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nq5t
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« Reply #9 on: April 06, 2018, 04:22:23 PM »


As I continue to clean the radio up I find the gray plastic knobs are kind of flakey. There seems to be a chalky buildup that will not come off. It might be best to leave them alone for fear they might crumble.

Rich

I don't recall the specific chemical details, but it's a byproduct of the type of plastic National used in the knobs and effects most of these radios.  It should clean up fine — mild soap, water, and a toothbrush.  Maybe have to use a toothpick in the sharp corners in the grooves.  I've never heard of anyone's knobs crumbling because of this … but there's always "one" somewhere :-) 

After cleaning them up, I did notice some of it coming back here and there at some point in time.  Just cleaned it off with a toothpick.  I'd thought about giving each knob a coating of hard carnauba wax, but never did it, and don't know whether it would have done any good anyway.
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Carl WA1KPD
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« Reply #10 on: April 07, 2018, 08:59:50 AM »

Actually one of the more interesting rcvr I had was an original Super Comet. There is no AF or RF gain control. All is accomplished by an IF gain control. The BFO was plenty strong, so the system orked fine.
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kb4qaa
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« Reply #11 on: April 08, 2018, 04:13:19 PM »

Dittoes, on mild soap, warm water and toothbrush.  Follow up with a good wax and buff with a soft cloth
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