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 Post subject: National NC 2-40 D cabinet question and feet
PostPosted: Jun Wed 05, 2019 10:49 pm 
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I have a National NC 2-40D that I want to remove from the cabinet. I don't want to mess up the bandswitch/tuning mech by just guessing. Any video links? I poked around Youtube, but find nothing but clips showing them playing.
RW

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Thu 06, 2019 5:52 am 
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You can remove the receiver from the cabinet, or perhaps more accurately, take the cabinet off the chassis, without disturbing the band switching, Dial assembly, or catacomb. Click on either of the pics below to go to more detailed pics of the radio. Once there click on the various pics to navigate through the various folders.

Image

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Thu 06, 2019 1:53 pm 
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I knew Mike or Rodger or both would be quick to respond. :D

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Thu 06, 2019 7:05 pm 
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Will do, once I get home from work. The work computer uses that silly Microsoft Internet Explorer, and won't display the pics.
RW

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Thu 06, 2019 8:11 pm 
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Great looking radio, Mike.

Norm

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Fri 07, 2019 12:55 am 
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Mike...yours an earlier run? Your pics show paper/wax caps, but mine has those black beauties in it. Also, the speaker connector in mine appears to have been modified. That may explain why when I plugged in the speaker and powered up the unit, it blew the 1 amp fuse. I can't be sure as yet if the speaker that came with it is the correct one.
RW


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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Fri 07, 2019 3:45 am 
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The connector on the end of your speaker's cable looks to be "stock", so it seems the original chassis connector was replaced. The original socket was a cheap two layer phenolic type which weren't all that rugged.

You'll notice the mounting holes are in a different location. That's because the pin orientation on the replacement socket was rotated 90* from the original. Those sockets are a standard 5 pin tube type, like an 807.

Image

-----------------
As for the fuse problems, I'd pull the rectifier and see if it still blows the fuse. If it does, either the transformer is "toast" or there is an AC power wiring/component problem.

If the above is OK I'd replace both of the PS filter caps and give it another try. I cut the wires on my filters and left them in for "looks" top side, and put new ones on the bottom side of the chassis.

Image

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Fri 07, 2019 11:25 am 
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I should have mentioned it works with headphones. Could be a problem with speaker transformer? And I'm working on replacing filter caps.
RW

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Fri 07, 2019 4:42 pm 
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The transformer could be OK and the speaker is open. Check it all with the Ohmeter.

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Fri 07, 2019 6:51 pm 
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Yep. Plan on doing that. Busy weekend coming up.
RW

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 Post subject: More on National 2-40D
PostPosted: Jun Wed 12, 2019 10:04 pm 
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I'm trying to locate feet for mine. I thought there was someone on Ebay a few years ago selling either NOS or New parts. I can't find anything about that. Is there some that makes them? Otherwise, I can post in the Wanted section here, and on Facebook.
RW

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 Post subject: Re: National NC 2-40 D cabinet question
PostPosted: Jun Wed 12, 2019 10:52 pm 
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Finally checked the VC...digital meter gives .6 ohms. At least it's not open.
RW

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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Thu 13, 2019 1:12 am 
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I have no idea why the feet are missing from so many of this series of receivers but someone must have a National foot fetish with a box full of them. I see so many of them for sale on ebay without the feet and also at hamfests. My first one came footless but I found some via the regional AM net.

Glen sells reproductions on his website: http://www.k9sth.net/z-communications-company-2.html

Rodger WQ9E


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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Thu 13, 2019 1:18 am 
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Roger...I think that is the one I saw for the feet. Guess I was wrong about them on Ebay, unless he sells them there.
RW

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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Thu 13, 2019 1:42 am 
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I think that he might also sell on ebay or maybe did in the past. I think I saw some of his Heathkit stuff up there.

I suspect someone who is good with 3D printing could replicate these easily. I have been planning to pick up a 3D printer and one of my nephews who is heavily into 3D printing has reminded me of this several times but other projects keep getting in the way.

Rodger WQ9E


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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Thu 13, 2019 3:22 pm 
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Let me tell you guys, that speaker connector is really cobbled up. Wires not there that are supposed to be; a ground wire where there is not supposed to be one; ...And the schematic supplied in the manual don't help much. I found the Sam's for it...a little better detail...even though it is for the DR and DT versions. I don't know which one I have anyway. So I'm going to be on the struggle bus for a bit with this tank. I mean boat anchor.
RW

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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Fri 14, 2019 1:34 am 
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I give up. I can't follow the schematic versus the wiring...on the battery socket and speaker socket. Neither the Sams or manual give pin-outs on those sockets. Things just don't see wired at all like the schematic shows. SO. Anyone near the West Michigan shoreline/Holland area that will check this for me? I have never had such a difficult time on any radio so far. And I've worked on at least 25 in the last 7 months. But then, none have had inscrutable modifications like this thing. :twisted:
RW

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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Fri 14, 2019 2:07 am 
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RW,

Let me try to walk you through this one. Since it has been modified I wouldn't trust the schematic for wiring the plugs anyway. Start with the speaker socket because it is simple. Make a diagram of your socket as you trace the leads so you will know what they should connect to on the external push/pull audio transformer/speaker plug. One pin of the receiver mounted socket should go directly to chassis ground. Two of the remaining pins will each go to each of the output tube plate connections at the 6V6 tube sockets. One of the remaining pins connects to the output of the power supply B+ filter (terminal of L1 NOT connected to L2), and the remaining pin leads to the parallel connected screen grids of the output tubes.

The speaker plug must be wired so that the pin to the center tap of the push pull primary of the speaker mounted output transformer mates with the receiver socket contact that carries the B+ supply output. This plug also has a jumper from this pin to the pin that interfaces with the receiver socket contact leading to the output tube screens. This is a safety measure using this jumper to protect the output tubes from being damaged through the application of screen voltage without plate voltage. A lead from each side of the speaker mounted output transformer primary connects to the pair of pins corresponding to the receiver socket pins that connect to the 6V6 tube plates. If the wiring on the speaker plug isn't obvious, use your ohm meter to determine the primary center tap and the two end leads. The resistance from primary winding end to end will be roughly twice the resistance from the center tap to either end. One lead on the speaker end of the plug will be grounded typically to the output transformer and/or the speaker cabinet and this lead corresponds to the grounded contact on the chassis socket.

From your photo, that transformer looks pretty small on the speaker so make sure that it is really a push/pull (tapped primary) output transformer and not just some straight audio impedance matching transformer.

You need a dummy plug in the battery connector to:
1. complete the primary circuit, you can trace which leads are involved by using your ohm meter to trace to the fuse and the power switch, this jumper on the battery plug simply completes the circuit from the fused input lead to the input of the power switch.
2. complete the 6.3 volt filament circuit ground return. The jumper ties one end of the 6.3 volt filament winding to ground with the other side feeding the filaments.

Good luck and when a radio is modified you have to resort to using your eyes and meter rather than the schematic.

Also keep in mind that full B+ voltage is on all but one of the leads to the external speaker so make sure the insulation is intact and treat them with respect.

Rodger WQ9E


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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Fri 14, 2019 2:53 am 
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Ok...pins 3, 4 and 5 are wired correctly. 2 goes to ground. And 1 to L1. But what has/had me hung up is neither schematic gives socket or plug pin outs. Schematically it is wired right. The transformer on the speaker does have a center tap, so that's good as far as that goes. And just checked the resistance of the primary of the output, and between both ends, I read 204 ohms; between one end and center tap, I get 233 ohms. And between the other end and CT, I get 438 ohms. The VC reads .6 ohms. Transformer secondary reads .9 ohms. The speaker itself is also wired right to it's plug.

The problem is, when I had the speaker plugged in, and turned on the radio, it popped the 1 amp fuse. That is what I am trying to figure out.
RW

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 Post subject: Re: National NC 2-40 D cabinet question and feet
PostPosted: Jun Fri 14, 2019 3:28 am 
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The 220 and 110 volt primary circuits each have their own fuse holder, F1 and F2.

The 220 Volt fuse is called out as a 1 Amp in the parts list, while the 110 Volt fuse is called out as a 2 Amp.

If you have a 1 amp fast blow Fuse in the 110 Volt holder, it most likely will pop even if everything is OK.

You might double check.

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