Unknown National

[WQ9E]

I have a NC-183D variant on the bench. It is a diversity model but appears different than the usual Northern Radio versions.  It is a dual conversion like the normal NC-183D, covers broadcast through 10 meters but not 6 meters, has 20 tubes and 3 added controls (fast/slow AVC, int/ext HFO, and bandwidth).  On the back are controls for AVC DX/local, IF gain, and 1265 oscillator in addition to various inputs/outputs.  After replacing a number of bypass caps and a few resistors it is working well but I would like to find more info if anyone is familiar with this particular variant.

[W2PFY]

Well first of all stop all work and send it to me

I think that receiver may have been used in conjunction with the Northern Radio Type 115 Model 1.

I was surprised to see that there was so much information via Google on these units. They used the above model in the Navy for signal injection for diversity reception. Maybe that is what you have?

There is one for sale on ebay right now at a big price but it may be just the thing for that receiver?

Please let me know if you think I am on the right path as I profess to know nothing

[N8ETQ]

Hey Rodger,

     It looks like the upper left corner of the front panel
is drilled for a missing nomenclature tag.  I was thinking
a "Northern" diversity setup too but I had a National
NC-400 here a few years ago with similar additions.
It was modified by "GloTrack".

GL

/Dan

[WQ9E]

Terry,
Thanks for the information on the external oscillator and I have added it to the "clues" for this unit.  I thought at first it was going to be pretty close to the NBS-1 I own but it is very different.  I have gone from very simple with restoring the Aero International 4 regen to this multi-tube national variant and it is a bit of a technology shock.

Dan, I wish that little plate was still there since it would probably tell the story about this receiver.  That is a very cool looking NC-400.  I have a pair of regular NC-400 receivers but I have never seen one like yours and that is the first I have heard of "GloTrack".   It has a 60s psychedelic ring to it

The NC-183D whatever seems to be working well and for now I am going back to practicing my regen skills using the Aero along with a nice mixture of bourbon, eggnog, and orange juice to relax with

[nq5t]

This receiver also has a slightly different IF strip (at least from the IF tranny layout).  Than the typical 183D. Interesting ....

[W2PFY]

http://www.virhistory.com/navy/navy-rcvrs.htm

Check out the R-651/AN/URR 39 RECEIVER on this site. I think that is what you have.

Your receiver seems to have more on the rear apron.

[K4NYW]

I don't think it is an R-651/URR-39 (NC-183MR)- the band coverage and bandspread dial markings are quite different.
cheers,
Nick K4NYW
www.navy-radio.com

[VE3AJM]

Hey Rodger

Its the same receiver that I have here. I've owned it for over 10 years but there is very little, if any information available about it online. I have seen the ER article/picture, but this is a different 183D variant. I did get it working. The selectivity seems quite a bit broader with this 183D than the other National 183D I have here.

The ID plate printed:  Northern Radio Company, Dual Diversity receiver, Type 141 Model 2.

Al VE3AJM

[WQ9E]

Hi Al,

Thanks for identifying the receiver! 

This one had a number of leaky bypass caps in addition to 3 way out of tolerance 47K resistors.  The only oddity was it looks like the cathode bypass for the AVC amp was replaced sometime in its life and it was mounted away from the tube under some other components so I missed it initially.  Running with AVC on resulted in greatly reduced gain since the replacement cap was a dead short effectively removing cathode bias from the AVC amp.

I haven't compared it directly to my "normal" NC-183D yet but the non-crystal selectivity definitely strikes me as broad.  Switching between the 3 bandwidths is noticeable but not overwhelming.  I hope to get my NBS-1 on the bench in a few days to see how much effect its variable bandwidth control provides.

[w3jn]

The NBS-1's bandwidth positions are fairly apparent.  The IF cans need to be properly aligned for that to happen, however.

Very cool RX, Rodger, thanks for sharing the pics!

[WQ9E]

The National receiver is finished.  I had to do a bit of additional work.  National uses a resistor in the B- return to provide bias voltage for the RF gain/AGC system, in the NC-183D this is a 500 ohm unit.  The output stage cathode resistor is connected to this junction so that output stage current doesn't flow through the bias resistor but the current for the other stages does.  This modified National has additional tubes and the increased current caused the negative voltage to be around -60 instead of the stock -39 so even with the RF gain full on and no signal there was higher than desired negative voltage on the control bus. 

I thought about simply reducing the value of the resistor to return the negative voltage to spec but the additional 40 mils is drawn through an already heavily loaded filter choke.  Unlike many of the Hallicrafters receivers National takes power for the final stage from the low ripple side of the choke.

I found that the series resistor for the 0B2 regulator was less than the 3,900 ohm unit specified by National and the 0B2 was drawing excessive current.  Increasing this to the specified 3,900 ohms helped.  I then removed a 12AU7 which provides a couple of buffered outputs I am not using which helped further and I then switched to a 5K resistor for the 0B2 which still provides the minimum "keep alive" current under heavy load with the line voltage dropped to 112 (lower than I expect mine will ever go).  With this resistor value and the non-needed 12AU7 removed the negative voltage is about 5 volts high indicating around 10 mils of current flow over stock.  Running this way the receiver operates normally and the choke seems happy.

After a careful alignment the 3 position selectivity is definitely noticeable and although it isn't up to the variable selectivity provided by the pre-SP600 Super Pro family it is very useful for AM and the receiver works pretty well under battle conditions without having to use the fidelity destroying crystal filter.  Audio sounds great and it is very sensitive.  This one is a keeper and will end up paired with a Ranger 2.