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 Post subject: National SW-3 and What's this rare tube worth?
PostPosted: Jun Fri 14, 2019 6:23 pm 
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Joined: Nov Wed 28, 2018 2:29 pm
Posts: 16
At least Radiomuseum calls it rare; A De Forest Audion 435. The other two are RCA Radiotron 235, and RCA Radiotron UY-227.

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We got this SW-3 on the cheap, along with an Eico 2036 amp and some other stuff.

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The radio has two coils with it; one has the 'bandspread' trimmer on top and the other doesn't. Will it work with these coils, or do they have to be pairs of the same?

The heaters have continuity; what is a good tester (that I can acquire) for checking these old tubes? These questions and more!

I am looking for the dogbone power supply 5880 AB with 4-prong socket.

Thanks,
Simon


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Fri 14, 2019 9:46 pm 
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Joined: May Wed 03, 2006 4:47 am
Posts: 5352
Location: Radio Heaven, North Carolina, near Charlotte, 28106-3015
It needs a dog house power supply, not dog bone.

_________________
73, Ron w4ron
http://radioheaven.homestead.com/menu.html


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sat 15, 2019 12:18 am 
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Joined: Mar Sun 09, 2008 8:05 am
Posts: 538
Location: San Jose, California
It's worth a few dollars more than any similarly numbered globe-shaped tube from that time -- pre-1932. It won't make you rich. The SW-3's are great little receivers but, yeah, you need the correct dog house supply for it that puts out 2.5 volts for the filaments at least. The coils are difficult to come by. You'll need to decide whether you want general coverage or the the band spread ones like you appear to have. And of those, there are are some three different variants depending on when your SW-3 was made. Me, I'd just buy or make coil blanks and then wind my own as the specs for doing so are on the 'net. They also come up frequently enough on eBay.


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sat 15, 2019 1:31 am 
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Joined: Nov Wed 28, 2018 2:29 pm
Posts: 16
Ron in Radio Heaven wrote:
It needs a dog house power supply, not dog bone.

:oops: oop sorry, that was rather BONE headed of me :mrgreen:


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sat 15, 2019 1:36 am 
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Joined: Nov Wed 28, 2018 2:29 pm
Posts: 16
Thanks KJ6OFC, only one of them is a ‘bandspread’ Coil (I think); the other doesn’t have the trimmer cap on the top; I guess it worked that way, ‘cause that’s the way we found it, right?


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sat 15, 2019 12:08 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1052
Location: St. Louis, MO, USA
Someone used to make blank coil forms that have that unusual pin configuration. Che k the internet for information on how to wind SW-3 coils.

Dennis


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sun 16, 2019 1:08 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1322
Location: Roslyn,Pa 19001
As mentioned it is an early version the later models used ceramic for the 35's and the coil sockets. Also the tuning on the later set is a dual gang not two single gang caps w/a couple connecting them together.
https://www.qsl.net/wa9wfa/sw3version1.htm

Your set is in good condition typically the power cord/plug are ratty and the case/chassis will have a number of extra holes. Looks like the audio coupler has been replaced w/ a newer one and the voltage divider resistor is facing 180 deg out (tabs should face the front). Would give it much thought if the resistor is good.

If you don't want to bother w/finding a p/s that can provide 2.5v for the heaters swap out the tubes and lamp for 6v ones. That would be a couple of 36's and a 37 or 76. Then you just need abt 150v for the b+ and of course 6v.

The coil set you have looks to be for 80mtrs and are bandspread coils. A fine band to use the SW-3 on as the drift is very minimal and will tune from abt 3450-4020kc. Use the coil w/the trimmer for the det (the right hand socket) and if you need to use the trimmer on top to set the high end of the band.

GL
Terry N3GTE


Last edited by Radioroslyn on Jun Mon 17, 2019 2:50 am, edited 1 time in total.

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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Sun 16, 2019 7:09 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1322
Location: Roslyn,Pa 19001
>Will it work with these coils, or do they have to be pairs of the same?

Sorry got a little off track. To answer your question bandspread coils will have the pigtail and connector for a grid cap. General coverage coils don't. With the gc coils you'll notice that there is a grid clip that is clipped the a insulator on the divider in the cabinet. Use these grid clips when using the gc coils. With the bs coils w/the trimmer always goes into the socket on the right (like your photo).

Both coil sets (gc or bs) must cover the same frequency. In other words using a rf amp coil that covers 40mtrs and a det coil that covers 80mtr won't work. Some coils have a number stamped into the bottom. Older coil sets will have a color band to indicate the frequency.
https://www.prismnet.com/~nielw/sw3coils.htm
GL
Terry N3GTE


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Tue 18, 2019 4:02 pm 
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Joined: Nov Wed 28, 2018 2:29 pm
Posts: 16
Thanks, Radioroslyn for clearing up a lot of questions I had, and the link to the coils....so I have the 14A(Green)like you said for 80 meters.
I think I will find or build a 'battery eliminator', or use batterys.
Will need to find a headset.
The RF gain control lever barely moves, so things need to be limbered up and lubricated.
Interesting about the voltage divider resister, will check out the circuits to see if things are kosher.
Will get back to this project after I finish another I'm supposed to be working on :)
Regards,
Simon


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 Post subject: Re: National SW-3 and What's this rare tube worth?
PostPosted: Jun Tue 18, 2019 6:52 pm 
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Joined: May Fri 01, 2015 2:33 am
Posts: 1322
Location: Roslyn,Pa 19001
This set wasn't really set up for battery use. It's known as a SW-3AC The battery models don't use the multi tap voltage divider resistor as they tend to run the B batteries down. The battery models use series resistors to develop the proper B voltage for the different stages. If you like shoot me your email address via a pm and I can send you a bunch of files regarding the SW-3. Some are kinda large.
GL
de Terry N3GTE


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