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Author Topic: $50 score  (Read 14849 times)

N4NYY

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$50 score
« on: November 30, 2013, 05:20:38 PM »

I picked up an immaculate receiver for $50. Have not tried it yet. Need new power cord. I will post pics tomorrow.

It is National NC-101X. Same as in this pic http://www.qsl.net/k2vco/NC101X640.jpg.

Anyone know anything about it? LOL


« Last Edit: November 30, 2013, 05:27:56 PM by N4NYY »
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AA4PB

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RE: $50 score
« Reply #1 on: November 30, 2013, 05:25:26 PM »

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Bob  AA4PB
Garrisonville, VA

N4NYY

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RE: $50 score
« Reply #2 on: November 30, 2013, 05:30:12 PM »

http://www.prismnet.com/~nielw/nat_list/nc100.htm

Here's some specs


Thanks. Mine is slightly different from this line. I have a limiter switch/knob on the bottom row where the logo is pictured.
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AC5UP

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RE: $50 score
« Reply #3 on: November 30, 2013, 06:43:05 PM »

12 tubes and all of them metal...... Transformer power supply, too.   Can you relate?

Promise me you won't paint it hammertone green or align it against the Iggy.  National made some righteous goods.  Try to keep it that way........  ::)

N4NYY

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RE: $50 score
« Reply #4 on: November 30, 2013, 06:56:23 PM »

12 tubes and all of them metal...... Transformer power supply, too.   Can you relate?

Promise me you won't paint it hammertone green or align it against the Iggy.  National made some righteous goods.  Try to keep it that way........  ::)

Front panel is immaculate. Green? Hmmmmmmmm
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K8AXW

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RE: $50 score
« Reply #5 on: November 30, 2013, 08:45:16 PM »

Yea man!  Heathkit green!
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A Pessimist is Never Disappointed!

N4NYY

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RE: $50 score
« Reply #6 on: December 01, 2013, 06:30:55 AM »

Anyone one the impedance of the speaker? I have to make a temp one to test it.
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AC5UP

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RE: $50 score
« Reply #7 on: December 01, 2013, 06:54:36 AM »

Stay tuned...........

We may get a repeat performance of the day when Vinnie pondered aloud how in the hell can a 5 1/2" replacement speaker have mounting holes on 4 3/8" centers. The holes would be in the paper cone, wouldn't they? The original speaker was sitting right in front of him and a moment spent with a tape measure could have answered the question with time to spare but I guess the keyboard was closer than the steel tape.

BTW, Mr. N4NYY: I'll assume you've found this on BAMA  --  http://bama.edebris.com/download/national/nc100/nc100,101Xmanual.pdf   If not, it will be useful.

The book does not mention the speaker impedance but given the vintage the original was probably 3.2 Ohms and a 4 Ohm replacement should be the hot ticket.

What'cha got there is a fairly sexy example of pre-war engineering using classic glass-FET's. Note that with the exception of the 6C8 dual diode all tubes are single section. In one way that's good in that you won't have any issues with half a tube gone soft while the other half plays well enough to confuse your troubleshooting. OTOH, there is more point to point wiring needed for single section tubes and twice the number of tubes. Which can lead to stray capacitance issues and make it all the more important that you stick with the factory parts layout under the hood. In the book it looks like almost everything is true N-S and E-W so this is your chance to go perfectly anal. Other cool items of note are the transformer coupled phase inverter driving the 6F6's. A 6SN7 (the 12AU7's older brother) did that job 90% of the time but early Hi-Fi lore says a transformer sounds better. (?) You'll also find the 6F6's run ungodly hot so watch your pinkies in that corner of the chassis. And don't forget to nuke all waxed paper tubular condensers on sight. They are Satan's little radio tampons.

I think the sliding coil pack is mega-cool in concept but I have a hunch that unless the contact pins are of superior quality the switch can be one sweet pain in the ass at the age of 73.

No Joke... The book is dated 1940.      :o

AA4PB

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RE: $50 score
« Reply #8 on: December 01, 2013, 06:57:28 AM »

According to: http://www.virhistory.com/ham/speakers.htm the speaker is a National DCS-10 which is 10-inches with a 500 Ohm impedance.

You could probably use an 8 Ohm speaker along with a 70V line transformer.
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Bob  AA4PB
Garrisonville, VA

AC5UP

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RE: $50 score
« Reply #9 on: December 01, 2013, 07:08:17 AM »

Whoa......... Didn't see that one coming!

Very unusual to see that in consumer goods but also unusual to see the 6F6's in push-pull. The amplifier is good for maybe 10 - 12 watts and with a 500 Ohm output would be capable of driving 70 volt PA hardware directly. As Vinnie knows, small 70 volt PA transformers can be found at Duh'Shack right on the shelf. Except in New Jersey.

N4NYY

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RE: $50 score
« Reply #10 on: December 01, 2013, 07:36:35 AM »

According to: http://www.virhistory.com/ham/speakers.htm the speaker is a National DCS-10 which is 10-inches with a 500 Ohm impedance.

You could probably use an 8 Ohm speaker along with a 70V line transformer.


5UP pointed me to Radio Shack. The transformer is selectable to power out. Should I use 10 or 15W wiring to the amp?

BTW, Now I am thinking of trying to replicate a speaker.
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AC5UP

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RE: $50 score
« Reply #11 on: December 01, 2013, 09:15:37 AM »

IIRC the power thing on the transformer is intended to give the PA installer a choice between full volume and reduced volume in a smaller room next to a larger one. Check the installation instructions to confirm. If so, you'll want the 15 watt setting as that should be best efficiency.

AA4PB

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RE: $50 score
« Reply #12 on: December 01, 2013, 10:01:59 AM »

Although it probably won't matter much, 70V at 10W = 490 Ohms which is a pretty good match to the original 500 Ohm speaker. The 15W tap would present a 326 Ohm load.
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Bob  AA4PB
Garrisonville, VA

AC5UP

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RE: $50 score
« Reply #13 on: December 01, 2013, 11:02:47 AM »

This transformer is supposed to be available in stores, and only $2.99:  http://www.radioshack.com/product/index.jsp?productId=2103254&filterName=Type&znt_source=SearchStripe&filterValue=Transformers&znt_content=Transformers

Spec says 1,000 Ohms in to 8 Ohms out. No power rating given, but assume maybe a watt or two as it's small. So if a doofus wired half the primary to an 8 Ohm speaker on the secondary and didn't crank the volume too hard it should be enough to.............

AA4PB

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RE: $50 score
« Reply #14 on: December 01, 2013, 11:32:25 AM »

It should work okay.
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Bob  AA4PB
Garrisonville, VA
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