Hi All, I picked one of these up this weekend and I was curious to see if the date of manufacture could be determined by the serial number. The serial number on mine is 210 2024. This one is nice and clean too.







Thanks,

Doug

That looks nice and clean Doug. The NC-57 was a pretty effective performer in its day and price range which was one step above the AA-5 variety.

One way to approximate the age is to see if the filter can has a date code. Another is to find a manual on BAMA or elsewhere that has a manual with the 210 production run # on the back page. It will have a code with month and year of that runs release such as 352.

Carl

Hi Carl, I looked on the back cover of the manual that came with the unit and the code was ??1-4000-9-47. I couldn't read the first two numbers. Under that number was ER-210, so this would appear to be Sep 1947. Correct?

Doug

The NC-57 was made between 1947 to 1950. Ihave one its a ok radio does great till you get to the top band then it gets a bit weak in receiving.I recaped mine and did aligenment .Sounds good to me on the broadcast band.Angelo

I have some fond memories of the NC-57 that I had. Time frame was late 1966 or so. That NC-57 was so much better than the old S-40A that I had it was pitiful. Even if it was not very hot on 15 and 10 meters, it did open up the 15 meter band for me.

I recall coming home from school and turning everything in my bedroom on and that included the NC-57 along with a Multi-Elmac AF-67. 15 meters was hot on one particular day and the Japanese were rolling in like gangbusters. There were several of them calling CQ on AM phone, so I said to myself, what the hell.

However, when I threw the B+ switch on the homebrew power supply for the AF-67, I was greeted with a POP and a bunch of white crap spraying out from the power supply. That is when I learned the hard way to NEVER use old filter capacitors salvaged out of an old TV set, even if they looked good.

So, it still did not keep me off the air that afternoon. I pulled the fuse on the primary side of that split power supply and ran a wire jumper from the low (250 volt) power supply over to the 500 volt supply and I got on the air running about five watts on AM phone. The old capacitor blew its guts out, so I clipped it out of the circuit and went on to see if I could work any JA stations before the band dropped out for the night.

And that, I did. I responded to a JA1 calling CQ and he came right back to me and we chatted for about fifteen minutes before the band started folding for the night. Running five watts AM on fifteen meters with an NC-57 receiver and working JA stations. How much better can it get?
Curt

These are nice little receivers for the time. I had a NC-57B when I was in grade school. The " B " model allowed you to run it on storage batteries when AC power was not available. A few years ago I purchased one from a List member. I have recaped it, did a full alignment. Great for tuning across the bands. As you stated, not to good on the higher frequices. One thing you can do is to replace the two 6SG7's with 717A's, this will improve the gain and lower the noise floor of the IF. A good tuneable preamp for 20 meters and up will be a great help. I also spent some time getting the BFO coupling ( gimmick cap ) tweeked. allows one to copy CW and SSB with a good audio filter. I have been lucky enought to find a SM-57 S-Meter and Slect-O-Ject ( Band Pass / Band Reject ) Audio filter for mine. My main use now is to listening to the BCB, and with a good large Full range speaker pluged in the audio is not have bad. Good Luck wth Yours.

Yep, Engineering Run 210 Sept 1947. National put a bit more effort into the front end than Halli and it shows. And since they made their own IF assemblies they didnt buy the cheapest (widest) ones in a vendor bidding war.

In later years (60's) they did go out to bid and IMO so did the quality. The 7 years I spent there was enjoyable, stresssful at times, and Im glad I went thru it.

Carl

"The " B " model allowed you to run it on storage batteries when AC power was not available."

Mine has the X1 power socket on the rear with the AC jumpers. The manual has instructions on how to wire an octal plug for battery operation. is there another model that doesn't have this socket?

Mine also had that octal socket in the rear. Not only was it for possible battery operation, but it provided access to the filament and B+ voltages to run accessories such as a Q-Multiplier and such. I honestly can not remember if the set I had was a "B" model or not, but having an octal socket on the rear of the chassis apron with a shorting plug plugged into it was fairly common with receivers back then. I think my old S-40A also had one, but it may have been a five pin socket instead of octal.
Curt

I recently bought a basket case NC-125. Comparing to the NC-57, they look very similar. The 125 has the meter and select-o-ject built in but does not have the top band or built in speaker that the 57 comes with. Otherwise, schematically and even physical chassis looks the same.

I'm thinking that I might have to strip the 125 down to bare metal, which might be more of a project than I want to take on. But I'm finding these national receivers interesting. I started with the NC-183 in the fall, which I really like - a lot. I just got finished working over an NC-300, which is less of a 'dream' receiver than I though it might be. I'm hoping that this 125 will surprise me.

arnie - W1GCI

I have a NC-57M around somewhere... I have the covers off and knobs and such. The NC-57M was designed for the Yachstman so it could run off marine batteries. I need to dig that puppy out.

The 717A will work better in the RF stage, if you use in both IF stages it will mess up the AGC. The 6SB7Y was a god choice for the mixer.

Forget about the top band, thats pushing your luck unless the signal is extremely strong.

Only the NC-57 and 57B models can be run off batteries.

The NC-57M is strictly AC/DC, substitutes a 190-410kc marine band for the 35-54 mc band, and has no provision for any rear panel accessories.

Carl

hello all,

Someone just gave me a NC-57. The dial string for the bandspread is broken but I have the spring
and the clip. This looks like a challange to replace it. Could someone tell me what
the length is from the tip of the spring to the tip of the clip.

I have some string and want to make this up and give it a go.
The bandspread turns and changes frequency its just the dial for the bandspread
doesn't turn. So the string for the bandspead wheel is what I am looking for
the length on

Thanks,

Ken

Just when you give up looking you trip over what your looking for.
I found a link in one of the forums here.

Nice diagram of the dial strings and their measurements.

Ken

Would you care to share that link?
I have the dial stringing information from the oldradiofixerupperguy.com website, but he only lists the NC-46 in the index under National.
I am always looking for more radio reference material for my hard drive because there may come a day this when this information is no longer available.
The Sam's Photofact has a basic bandspread dial stringing diagram. The stringing in mine is intact and in good shape. I just cleaned and oiled the axles and pulleys. It has a nice heavy flywheel.
I purchased a NC-57 (ser# 277-0961) a couple of weeks ago at the AWA spring meet. I wasn't too sure what I had come home with, but I became more impressed with this radio the more I went through it. I may have been thinking of its poorer cousin the NC-33.
The NC-57 got a very good 4.3 out of 5.0 rating on the eham reviews. I replaced the leaky filter and wax caps. Some resistors had doubled in ohmic value or gone completely open, especially those in a stressed B+ duty.
It has many attributes of a good receiver, but is without an S-meter and xtal selectivity control. National made available an external octal socket plug-in S-meter (SM-57) and the octal plug-in for the factory S-O-J as options to make it a well-equipped radio.
So far I am impressed with its stability, sensitivity, fidelity and manners.
The National Service Notes on BAMA has a chapter of factory improvements for better band A; 50+ mc performance for the NC-57. It has had all the suggested upgrades done. I intend it to be my bedside SWL receiver for awhile.

Hello,

I will try and find the link again.

I had a problem with the BFO not working. If I injected a 455KHz signal from my signal generator at the output
of the CW circuit it works. This is the 6SN7 or 6SL7 (I have seen both in schematics) tube, I didn't have any Grid Bias
(-5.8v) After checking the componets in the 455KHz resonant circuit, including D.C. resistance in the coil, I changed
the .01uf cap on pin 5 of the of the 6Sl7/6SN7. The BFO started working. I then changed a couple other componets,
like a 100K that was reading 135K, and a screen bypass cap in the 1st I.F. amp. When I turned the receiver back
on the BFO didn't work. After spending several hours trying this and that I tried swapping the tube. In my
NC-57 I had a 6SL7. I swapped it with a 6SN7 and the BFO has been working every since.

Now I am just starting to read about alignment. I find my dial calibratoin to be way off.

Since my bandspread dial string was missing can you tell me if 100 is what they consider the set point
or is it 0 when performing the alignment. I did see a video on youtube and it looked like 100 is when the sections
of the variable capacitor are apart and 0 is when they are fullly closed. Apart would be min capacitance
and closed max capacitance.

Thanks,
Ken

Here is the link. You probably have it already but it was helpful to me.

http://www.antiqueradios.com/forums/vie ... p?t=111379

Ken

I believe that the 6SL7 is the tube specified for BFO (CWO) and 1st audio in the factory and Sams manual.
The Riders is the first time I have seen 6SN7 specified for this position. The 2 tubes don't have exactly the same characteristics.
I knew of no 'running' change in production concerning a tube change. Maybe yours is meant for a 6SN7?
I have found that the 455 kc IF frequency is fairly critical for the CWO to work. Any deviation more than a couple of kc will pass it out of the coil's adjustment threshold. You can't just adjust the IF transformers for loudest signal.
I remember as I brought my hand closer to the CWO coil, I could hear the high-pitch from the CWO begin to work. As I pulled my hand away, I could no longer hear the heterodyne whistle.
The coil will allow you some leeway if you loosen the PITCH shaft coupling screw and turn the coil slug with a hex key in the center of the PITCH control shaft, but this shouldn't vary from the factory setting unless values have shifted or someone previously messed with the adjustment.
The 'set' on the bandspread dial should have the capacitor plates fully open (minimum capacitance). You do your alignment with the bandspread plates fully open. Follow the alignment procedure in order for best results.
P.S. - The tube type designations are stamped in the chassis next to the tube socket. Does yours call for a 6SL7 or 6SN7?