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 Post subject: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 1:12 pm 
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Location: Somers, CT
How stable were the NC-303 receivers? I know most have a 6V6 in place of the fragile ballast tube--planning to make a solid state regulator drop in to keep the oscillator filament voltage constant and eliminate the hum modulation problem some have noticed on the higher frequency ranges.

I'm also wondering if a K4DPK VFO stabilizer is worthwhile, or a waste of time in this RX. The gentleman (Cambria??) who was offering less costly units from the UK has retired and closed down his cottage business and it looks like K4DPK is the only game in town?

Pete

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 2:44 pm 
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Peter,

Congratulations! It sounds like you bagged that NC-303 and it hopefully has arrived, or will shortly.
Per my posting on the other thread, my NC-303 was absolutely rock solid, even on 10M!
I set the NC-303 and SX-101A up on 10M, zero beat them in SSB mode to my service monitor , and then let go of the VFO's: The SX-101A promptly drifted off to frequencies unknown, while the NC-303 just sat there zero beat...
As far as the 4H4-C replacement goes, that's actually a fairly simple job: This is all by memory, as I'm out on Fire dispatch in Alaska at the moment, and don't have the rig in front of me.
I built a plug in solid state regulator adapter into a salvaged Octal tube base, and with the addition of a single ground return lead from an unused terminal of the tube socket to the chassis, there were no modifications to the receiver.
I did this so you could easily pull the regulator, and swap it with the original 4H4-C if you wanted, everything being plug n' play with no fireworks or removal of modification necessary to switch between the two.

-Find the filament feed to the 4H4-C.
-Connect a diode to this. Any 1N400x series should work. You're half wave rectifying it.
-The diode feeds the input of a 7805 regulator, also an electrolytic to your ground point. Maybe 10 uF...
-Take your 7805 ground lead, add two 1N400x diodes in series with it to ground (you are essentially raising the 7805 another 1.4 Volts, two diode drops, to give you 6.4 volts DC!).
-Add a small cap (maybe 1 uF?) to your 7805 output, then connect your output to feed the VFO filament.

This works well for me: A minimum of parts. It's not rocket science. I would put a small heat sink on the 7805.
Best of Luck with your NC-303!
I'll have to dust mine off this fall and put it back into service.

73, -Tom N1BEC/7


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 3:05 pm 
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Hi Tom

Yes, it is being shipped either today or Monday, double boxed so I hope it makes it okay. I am anxious to see how it looks, it's been over 50 years since I last owned a NC-300!

Pete

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 3:22 pm 
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Pete,

If you line voltage is stable, you won't need to worry about doing anything with the filament line but if you get a small drop every time a refrigerator or other heavy load comes up then it will be noticeable. There is a slight time lag between voltage sag and frequency shift given the thermal inertia. I have a 6V6 in mine and I don't notice any hum modulation issues.

Overall thermal stability of my 303 is on par with my SX-101 which I consider to be fine. They certainly aren't as stable as a modern DDS locked to TCXO setup but I think you will be happy with it in stock form. For someone who grew up in the synthesized era, it probably wouldn't be as acceptable. Since the NC-300 was promoted as the "Dream receiver" I presume you can call yours "Son of Dream" which sounds a bit like a thoroughbred race horse and the 303 was definitely a thoroughbred receiver of the era.

Rodger WQ9E


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 4:21 pm 
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That is the problem I have with the SX-101a--a heavy transient load does cause the frequency to jump. Otherwise it is quite usable on CW, at least for 80 or 40 meters. I'll probably add a solid state regulator to replace the ballast. Are there any good articles on modifications that are worthwhile for the NC-303 besides the ballast tube replacement issue?

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 5:28 pm 
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Peter,

I am not aware of any. There were some factory service updates for the NC-300 but I think these pre-date the NC-303 design revision.

Rodger WQ9E


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 5:43 pm 
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Have to agree with Rodger, the 303 is pretty darn good, stock. I do think the 300 is a bit better on CW because of the crystal filter but other than that, when the time comes, the 303 is going to stay.

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 6:25 pm 
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I had to repair a small mountain of 300's and 303's...
Although they both did well on AM, the 300 was a beast to use on SSB... The 303 was much better there...
Peter, you'll enjoy the 303. Wonderful receiver!

-Tom


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 6:48 pm 
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(Sounds like I should keep the 303 I stumbled upon)

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 6:56 pm 
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Sounds like I should have not let the 303 Peter purchased slipped away :lol:


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 7:25 pm 
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Now figuring out how to get either a Ranger I or Ranger II shipped to CT. Two offers so far, both pickup. Closest is 170 miles, one way. Full day driving.

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 9:34 pm 
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Hi Pete,

Wow, R23, Nc 303, Now a Ranger, sounds like 3 new projects in the last couple days. Either you're AWFULLY FAST, or the line's getting longer!!! :wink:

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 06, 2019 9:44 pm 
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Time is getting shorter, unfortunately. Ham bucket list stuff.

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Sat 07, 2019 5:37 am 
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Peter Bertini wrote:
Now figuring out how to get either a Ranger I or Ranger II shipped to CT. Two offers so far, both pickup. Closest is 170 miles, one way. Full day driving.


The SS regulator for the 303 sounds interesting. Thanks for sharing the details.

Peter, some years ago, I drove 700+ miles round trip in one day to buy my first AM transmitter, a Heathkit Apache, from Al W1UX, incidentally in Connecticut. I don't know that I would do it again, but I have enjoyed the Apache, and I was just thinking of that today while I was using it during an AM QSO. You'll probably feel the same way if you decide to make that trip.

A bonus during my trip to CT was enjoying lobster roll for the first time at a little eatery on the sound.

73,
Brad K4RT


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Sat 07, 2019 6:05 am 
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The SS regulator for the 303 sounds interesting. Thanks for sharing the details.
73,
Brad K4RT[/quote]

Brad,

Glad to share. Folks have shared a lot of stuff that's helped me, I'm more than happy to pay it forward.
I came up with the idea after seeing really complicated solutions to a very simple problem... This is probably as simple as can be reliably done to control the filament voltage.
FB on the lobster roll! Just had my first taste of real King Crab up here in Alaska... Grew up with lobster in New England...

73, -Tom N1BEC/KL7


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Fri 13, 2019 4:57 pm 
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MY GAWD, IS THIS THING A BIG BEAST!!!! HUUUUUUGGGGGEEEEE!

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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Sat 14, 2019 12:07 am 
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Oh, come on Peter.... It's not bigger than an R-390!


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Sat 14, 2019 2:32 am 
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The 303 came towards the end of the boatanchor period. Soon after SSB was the norm and either more compact receivers or transceivers.
When the Drake 1A came out, it got a lot of attention for being compact. Then the S-line/KWM-2, though maybe not so light.

Michael


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 Post subject: Re: NC-303 frequency stability question
PostPosted: Sep Sat 14, 2019 4:05 am 
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Pete,

Most all the old National, Hammarlund, and Hallicrafters receivers were essentially the same size.

Image

Image

Image

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