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National NC183D Questions




 
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June 19, 2019, 03:24:27 PM *
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Author Topic: National NC183D Questions  (Read 287 times)
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W3ON
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« on: June 12, 2019, 08:16:26 PM »

Hello
Recently I purchased a National NC183D at a local hamfest here in the Pittsburgh Pa area. It did not come with any manuals, schematics etc. I was told that it had been recapped, was operational, and had a NBFM adapter installed.When I  got it home I took a close look at it. It was, as I expected, the chassis was dirty. The cabinet, at the rear, had some major scratches. I then connected it to an external antenna at the SO239 connector, external speaker to the 8 Ohm terminals, and to a variac. I activated it, slowly using the variac. I did not note any electrical problems. I did note that it did appear to work properly. At that point I decided to clean the inside of the chassis. I have been doing this over a period of several days. I also cleaned the knobs.
Upon pulling the tubes and checking them against a list of tubes I found on the internet, I noted some discrepancies. I am wondering if I can get some advice as to why this was done. Or if I should get the original tubes. I found that:
V13 and V14 were 6W6GT. Not a 6V6GT.
V12 was a 6SN7. Not a 6J5.
V1 and V2 were 6CB6. Not a 6BA6.

The NBFM adapter is a NFM-07, uses a 6BZ6 not a 6AK5, and a 6H6.
From what I can find on the internet the NFM-07 is for a HRO50.

By the way, the serial number is stamped on the chassis is 372-0604. Anyone have information on that?

I have not yet removed the chassis from the cabinet. I am supposing that this unit has been modified

I have sent for some Electric Radio reprint magazine articles, and downloaded a SAMS Photo Fact.

Any information would be appreciated.

73 de Chuck W3ON
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KK4YY
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« Reply #1 on: June 12, 2019, 08:55:44 PM »

Chuck,

Well, a 6W6 is the same pin-out as a 6V6 so it should work, BUT it uses 1.2  amp of filament current as opposed to the 6V6 which uses .45 amp.

The 6CB6 and 6BA6 are different pin-outs, and the sockets would need to be rewired to be used. Same for the 6SN7 and 6J5 -- different pin-outs.

Maybe it was modified? Maybe it was a different version? I don't know.

Looks like you have some investigating to do.


Don
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w8khk
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« Reply #2 on: June 12, 2019, 09:20:42 PM »

Not only is the 6SN7 a different pinout than the 6J5, it is a dual triode where the 6J5 is a single triode.  So there may have been a modification adding some functionality.  Even the filament pins are different.

There may not need to be any wiring change for the 6CB6.  The two tubes have the cathode and suppressor grid interchanged between pin 2 and pin 7.  But in most cases, the suppressor grid and cathode are tied together, so if that is the case, the interconnections for these tubes would be identical.  The major difference is the 6AU6 is a remote cutoff pentode, which responds to AGC voltage, where the 6CB6 is a sharp cutoff pentode and has a much higher Gm.  If it is used as either an RF or IF amplifier, you may run into non-linearity and distortion.  Otherwise it should work fine. 

As an RF amplifier, the 6BZ6 is usually considered superior to the 6AK5 for intermod, but in the SSB adaptor it is probably a safe trade-off.
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Rick / W8KHK  ex WB2HKX, WB4GNR
Jim, W5JO
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« Reply #3 on: June 13, 2019, 03:44:24 PM »

You may have a later version of the radio.  The early version had a 6J5 as a Phase Inverter and the S meter was driven off the B- supply.  B- is above ground so do not short the case of the electrolytic filter cap to ground with the radio on.  Also the meter needle will rest to the left on this version with power off.

The version with the 6SN7 uses one triode as a meter driver and the other triode as a phase inverter and the meter needle rests on the right side when power if off.  Again do not short the case of the electrolytic cap to ground.

I also suggest that you obtain the diagram for the radio that uses the tubes stenciled on the chassis and check each tube socket for wiring changes to see if it has been modified for the tubes present in the set.  Also there are several different versions of the diagrams for the early and late versions.  The serial number will not mean anything concerning the diagram.

The tube numbers on the chassis should be a help in finding the right diagram.
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KK4YY
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« Reply #4 on: June 13, 2019, 04:07:06 PM »

Chuck,

You'll find the 6SN7 version, and others, here:
http://bama.edebris.com/manuals/national/nc183d/


Don
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W3ON
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« Reply #5 on: June 14, 2019, 11:11:28 AM »

GM All
Thanks for your replies. I have downloaded the manual, and schematic for the 6SN7 version of the NC183D.
I am awaiting the delivery or the Electric Radio magazine reprints, which should arrive in today's mail.
I did some checking of the tubes last evening, although I am not sure what I am looking at. Hi Hi.
If I am reading things correctly on my old Eico tube tester, it looks like I have quite a few tubes that may
need replaced, such as (4) 6BA6, (2) 6BE6, (1) 6AL5, (2) 6CB6, (1) 6SN7 tubes. Although the NC183D
did appear to operate normally.

Funny thing about my Eico tube tester, it states that their is some sort of MERIT
test reading. I cannot yet figure out what the MERIT test is or where it is on the meter. I guess I am
going to have to read up on that. Hi Hi.

I am still wondering about modifications, and why that NFM-07 NBFM adapter was installed. I did more cleaning last evening. It is definitely better than it was.
73 de Chuck W3ON
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w4bfs
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« Reply #6 on: June 14, 2019, 03:20:00 PM »

merit

typicaly a simple tester would drop the filament voltage 15 or so percent and observing the tube being tested if you saw the reading drop too much you would suppose the tube was loosing emission and therfore lacked merit

 Kiss Kiss Kiss
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Beefus

O would some power the gift give us
to see ourselves as others see us.
It would from many blunders free us.         Robert Burns
Jim, W5JO
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« Reply #7 on: June 14, 2019, 05:09:21 PM »

The NBFM was installed in the radio to  receive Narrow Band FM.  I forget the bandwidth allowance but was a semi-popular mode on 10 meters, especially in some areas of the country.  Six meters was also somewhat active in parts of the country on AM too so that is why it is included.
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