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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Tue 24, 2020 9:55 pm 
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rsingl wrote:
Dalton,

The NC-183D is a solid National receiver. There are two distinct versions with the earlier using a 6J5 as the phase inverter for the output stage and the later version using a 6SN7 with one section as a phase inverter and the other as a S meter amp. Just make sure to use the correct schematic for the receiver that you have to avoid confusion.

Some National receivers of this era left the factory with a .1uf capacitor from one of the rectifier plate pins to ground. If your receiver has this, remove the capacitor because it isn't needed. If it fails shorted it WILL take out the transformer before the fuse can open and a lot of National receivers ended up with new power transformers because of this useless capacitor. It was left out in later production and probably cost National a bit in warranty dollars even back then.

Regardless of version, it is very common to find the 47K screen resistors used throughout the RF and IF sections to have drifted to many times their marked value. This is from a combination of less than stellar resistor quality combined with these resistors operating at near their rated dissipation in many of these positions. Check the screen voltage (or resistor value) on them but if you find any of them out I would just replace all of them. This was necessary on both NC-183D receivers I restored along with the NBS variant based upon the NC-183D. It is a known issue with this set.

Otherwise there will be a few paper type capacitors (primarily the larger value units) that should be replaced but even in the early production most of the capacitors are either mica or ceramic disc. The filter capacitors will likely need replacement, definitely replace the output stage cathode bypass cap because leakage or a short here will potentially take out the audio output transformer and possibly the power transformer. All of these that I have been around came from the factory with reliable ceramic discs in the coupling/DC blocking position for the output tube control grids but if by chance your radio was built with paper caps here then replace them for the same reason you replace the output stage bypass capacitor.

Unlike many receivers, several National sets of this era hold the B+ return slightly above ground to develop bias for the output stage and RF gain control network. It has a separate filter capacitor for this section which is 25 uf @ 50 volts. Some versions of the manual incorrectly list this as a 25 pf capacitor so ignore the manual and use the marked value on the schematic and existing capacitor when replacing. Observe proper polarity when replacing this bias supply capacitor remembering that the negative lead of an electrolytic capacitor goes to the most negative potential part of the circuit, in this case it is the bias bus and not ground.

Rodger WQ9E



Thank you Roger!

In my reading, I did come across mention of the .1uf capacitor problem. In that case, it was not fully open, but was operating at about half capacity, causing a problem with sensitivity.

I know enough to understand what you are saying, and you identify most of the problems that are likely to arise. The 47K screen resistors were also mentioned.

The seller mentioned that there was something like oil under the transformer, but he was unsure if it leaked out of the case, or was something spilled on the radio.

Here is a screenshot, I think this may be what he was referring to.


Image

Hopefully this is not indicative of irreparable damage.

The seller did tell me when he plugged it in (I will use a variac!) that all tubes did light up.

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Tue 24, 2020 9:57 pm 
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Norm Johnson wrote:
You should enjoy this radio. It does not have a product detector but easily receives SSB. Mine was in terrible condition but was worth the effort to restore.

Norm

Beautiful restoration!

Thanks, Norm!




Tim
N3YQV

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Tue 24, 2020 10:03 pm 
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Dave Doughty wrote:
I'm glad you settled on a 183D. Besides the usual need to replace the paper and electrolytic caps, mine also suffered from out-of-tolerance resistors. The 470K units in the AGC circuit had gone way high or open. This led to several 6BA6 tubes developing grid emission which was a problem even after the resistors were replaced.

Properly restored and aligned, you will love this receiver especially its no-nonsense control layout and push-pull audio.

Dave


Dave, thank you so much!

I love both shortwave listening and a.m. dx'ing, when I heard this set offered hi-fi quality audio, was a truly hot receiver, and even had the 6 meter band, I was hooked!

A lot of times, when not bandscanning, I like to lay back with the radio on an interesting a.m. radio broadcast, and it sounds like this set would make that even more enjoyable

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Wed 25, 2020 12:07 am 
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Hi Dalton,

That Pic DOES NOT look good, it could well be the result of the capacitor Rodger mentioned, having failed, or some other transformer problem. I sure hope not.

National, as most other manufacturers, built radios in lots, and each chassis was marked with the Engineering Release number stamped as a 3 digit number as part of the complete serial number. Therefore, you can be sure you have the proper manual, assuming you are able to find one, based on the "ER" number as shown here. The ER number in this case is 372, and the actual serial number of the radio was 1,000.

Image

Below is the chassis "ER" and serial for another of my National radios.

Image


Manuals had the ER number stamped on the outside rear cover, showing this "Service Manual" number 3300, printed in August of 1946. Its the correct manual for the above radio.

Image

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Wed 25, 2020 1:17 am 
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It looks like that transformer in your picture did get very hot at some point in its life. Someone had already replaced the transformer in my 183D before me. They did remove the .1 uf cap connected to one of the rectifier plates but didn't replace the other leaky paper caps or the electrolytics. So the new power transformer showed signs of having been very warm. All is well now.

Dalton wrote:
In my reading, I did come across mention of the .1uf capacitor problem. In that case, it was not fully open, but was operating at about half capacity, causing a problem with sensitivity.
I don't think that's the capacitor Rodger and Mike were talking about.

Dave


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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Wed 25, 2020 4:25 am 
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Yes, upon review, I see that now. It was a 5 pF cap I was thinking of.

Thank you, Dave.



"A "eureka" moment
Testing again, I was listening to a weak station at around 18 MHz on band "B", the highest frequency shortwave band, RF and AF gains maxed while checking voltages at the second 6BE6 and its 1265 KHz oscillator / converter stage. I put the prod on the IF transformer side of the 22 ohm resistor feeding the input grid and noticed a slight increase in signal strength. Huh? Why would that happen especially since both sides of the transformer were peaked properly in alignment? As I moved the prod a bit while still touching that point, I could increase the sensitivity a bit more. I was either adding a bit of capacity or my voltage prod was doing regeneration or something.

Long story short, the culprit turned out to be the 5 pF cap between the two 1720 KHz IF transformers. It had passed the tests before when I fed the various points with a sig gen, monitoring via the scope. I suppose a very small 5 pF cap that is open inside can still be a 1 pF or so cap with just its leads in proximity. I replaced it with a new 5 pF silver mica and the two upper bands now had nearly the same sensitivity as the two lower ones. This was one hot receiver, especially since by now I had replaced the 6BE6 pair and all five of the 6BA6 tubes with new mil-spec versions in attempts to improve the sensitivity on the upper shortwave bands."

https://people.ohio.edu/postr/bapix/NC-183D.htm

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Wed 25, 2020 4:31 am 
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Mikeinkcmo wrote:
Hi Dalton,

That Pic DOES NOT look good, it could well be the result of the capacitor Rodger mentioned, having failed, or some other transformer problem. I sure hope not.

National, as most other manufacturers, built radios in lots, and each chassis was marked with the Engineering Release number stamped as a 3 digit number as part of the complete serial number. Therefore, you can be sure you have the proper manual, assuming you are able to find one, based on the "ER" number as shown here. The ER number in this case is 372, and the actual serial number of the radio was 1,000.

Image

Below is the chassis "ER" and serial for another of my National radios.

Image


Manuals had the ER number stamped on the outside rear cover, showing this "Service Manual" number 3300, printed in August of 1946. Its the correct manual for the above radio.

Image



Thank you, that ER number is greatly helpful!


Tim
N3YQV

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 5:02 am 
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Dave Doughty wrote:
I'm glad you settled on a 183D. Besides the usual need to replace the paper and electrolytic caps, mine also suffered from out-of-tolerance resistors. The 470K units in the AGC circuit had gone way high or open. This led to several 6BA6 tubes developing grid emission which was a problem even after the resistors were replaced.

Properly restored and aligned, you will love this receiver especially its no-nonsense control layout and push-pull audio.

Dave


I think I understand the leakage photo now.
It is looking at the plate underneath the transformer.
So, apparently transformer got really hot at some point.
If the set still turns on, it is possible the transformer has been replaced, but I wouldn't hold my breath (or try to run it without having it serviced. I have received a reply from Dlab regarding the possibility.)
With my luck, the seller held a flashlight up behind the dials to light it up. I notice the S meter isn't lit. :lol:


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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 7:03 am 
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Looks in nice condition.

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 1:37 pm 
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Don't know why, but I seem to have a fondness for these two arched dial receivers, the National NC183D and the Hallicrafters SX-100, but I do think the NC-183D was probably the prettiest receiver ever built. This is my second example and a keeper.

Image
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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 3:12 pm 
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Mikeinkcmo wrote:
Don't know why, but I seem to have a fondness for these two arched dial receivers, the National NC183D and the Hallicrafters SX-100, but I do think the NC-183D was probably the prettiest receiver ever built. ...


How can a guy with a beautifully restored NC-2-40D say such a thing?? :wink:

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 3:58 pm 
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jimbenedict wrote:
Looks in nice condition.

Thanks, after what I spent, that is comforting.

The radio was a little over $250, but the shipping from Saskatoon was over $100!

Before I try online auctions henceforward, I will try posting want ads here and at other radio sites.

The guarantee is the only good thing, about epay.

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 4:01 pm 
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Avery wrote:
Mikeinkcmo wrote:
Don't know why, but I seem to have a fondness for these two arched dial receivers, the National NC183D and the Hallicrafters SX-100, but I do think the NC-183D was probably the prettiest receiver ever built. ...


How can a guy with a beautifully restored NC-2-40D say such a thing?? :wink:


Probably easy when he sees the S-meter in between the two arches lit up and the needle moving! :lol:

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 5:18 pm 
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Quote:
...How can a guy with a beautifully restored NC-2-40D say such a thing??...


Oh, they're all nice, even the rat rods, for one reason or another, but now you're say'in I can't have more than one favorite?

Does that mean I haffta sell off the other ones?

OOOHHHH, what do do??? :(

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 5:26 pm 
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Mikeinkcmo wrote:
Quote:
...How can a guy with a beautifully restored NC-2-40D say such a thing??...


Oh, they're all nice, even the rat rods, for one reason or another, but now you're say'in I can't have more than one favorite?


Here's something I didn't know until now. According to Oxford Languages, "favorite" means No. 1, period, when used as an adjective:

Preferred before all others of the same kind.
"their favorite Italian restaurant"


But as a noun, it mean you just really, really like it:

A person or thing that is especially popular or particularly well liked by someone.
"the song is still a favorite after 20 years"


So I give you permission to have shelves full of favorites. No, no, it's okay. You don't have to thank me. Happy Thanksgiving. 8)

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Thu 26, 2020 5:39 pm 
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Avery wrote:
Mikeinkcmo wrote:
Quote:
...How can a guy with a beautifully restored NC-2-40D say such a thing??...


Oh, they're all nice, even the rat rods, for one reason or another, but now you're say'in I can't have more than one favorite?


Here's something I didn't know until now. According to Oxford Languages, "favorite" means No. 1, period, when used as an adjective:

Preferred before all others of the same kind.
"their favorite Italian restaurant"


But as a noun, it mean you just really, really like it:

A person or thing that is especially popular or particularly well liked by someone.
"the song is still a favorite after 20 years"


So I give you permission to have shelves full of favorites. No, no, it's okay. You don't have to thank me Happy Thanksgiving. 8)



:lol:

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Fri 27, 2020 12:10 am 
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I looked at the other pictures of the radio that you bought on ebay. None of the original paper caps have been replaced and there are a ton of them including lots of bumblebees which you can re-sell and get some money back. I do see one replacement electrolytic and several overheated power resistors. But I don't see and nasty modifications made by a previous owner. I think this set will be an interesting restoration project. Mine certainly was and it is one of my favorite boatanchors. I found it locally at a hamfest without its cabinet but with a matching speaker. This was years ago before skyrocketing prices. Still don't have a cabinet.

Dave


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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Fri 27, 2020 12:24 am 
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Dave Doughty wrote:
I looked at the other pictures of the radio that you bought on ebay. None of the original paper caps have been replaced and there are a ton of them including lots of bumblebees which you can re-sell and get some money back. I do see one replacement electrolytic and several overheated power resistors. But I don't see and nasty modifications made by a previous owner. I think this set will be an interesting restoration project. Mine certainly was and it is one of my favorite boatanchors. I found it locally at a hamfest without its cabinet but with a matching speaker. This was years ago before skyrocketing prices. Still don't have a cabinet.

Dave

Thank you, Dave!

I will not be selling this radio, that is for sure, and it is going to be #1 on my to be restored list.

I am looking at matching speakers, i take it the 10" National speaker is the correct one.

I also heard of people putting a better hi-fi speaker in the original cabinet to make the most of the sets great audio.

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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Fri 27, 2020 12:53 am 
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Dave Doughty wrote:
I looked at the other pictures of the radio that you bought on ebay. None of the original paper caps have been replaced and there are a ton of them including lots of bumblebees which you can re-sell and get some money back. I do see one replacement electrolytic and several overheated power resistors. But I don't see and nasty modifications made by a previous owner. I think this set will be an interesting restoration project. Mine certainly was and it is one of my favorite boatanchors. I found it locally at a hamfest without its cabinet but with a matching speaker. This was years ago before skyrocketing prices. Still don't have a cabinet.

Dave

I'm thinking this is the speaker.

Can't seem to find the ohms on it, I'm guessing 8?


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 Post subject: Re: National vs. Hammarland General Coverage Receivers
PostPosted: Nov Fri 27, 2020 3:45 am 
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Yes, that is one of two different but very similar speakers, shown in the pic below. Yes, one is closer to the camera but notice the distances from either end of the horizontal bar to the edge of the cabinet. Both the actual speakers are the same size only the cabinet is larger.

THIS SITE gives you information on just about all speakers made for ham radio receivers.

Image
Click the Pic

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